Icarus 221 (2012) 984–1001

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Spectral reflectance properties of carbonaceous chondrites: 8. ‘‘Other’’ carbonaceouschondrites: CH, ungrouped, polymict, xenolithic inclusions, and R chondrites

E.A. Cloutis a,⇑, P. Hudon b,1, T. Hiroi c, M.J. Gaffey d, P. Mann a

a Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9b Astromaterials Research and Exploration Science Office, NASA Johnson Space Center, Mail Code KR, 2101 NASA Road 1, Houston, TX 77058-3696, USAc Department of Geological Sciences, Brown University, Box 1846, Providence, RI 02912-1846, USAd Department of Space Studies, University of North Dakota, PO Box 9008, Grand Forks, ND 58202-9008, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 18 July 2012Revised 24 September 2012Accepted 17 October 2012Available online 26 October 2012

Keywords:Asteroids, SurfacesMeteoritesSpectroscopy

0019-1035/$ - see front matter � 2012 Elsevier Inc. Ahttp://dx.doi.org/10.1016/j.icarus.2012.10.008

⇑ Corresponding author. Fax: +1 204 774 4134.E-mail addresses: e.cloutis@uwinnipeg.ca (E.A. Clo

1 Present address: Department of Mining and Mater

We have analyzed reflectance spectra (0.3–2.5 lm) of a number of ungrouped or tentatively grouped car-bonaceous chondrites (CCs), possible CC-type xenoliths in an aubrite (Cumberland Falls) and a howardite(PRA 04401), a CH chondrite (PCA 91467), a CC polymict breccia (Kaidun), and some R chondrites. Thebest approach to analysis relies largely on characterizing spectrally active phases – i.e., those phases thatcontribute diagnostic absorption features, involving absorption band wavelength position, band depth,shape of absorption features, combined with albedo and spectral slope. Mafic silicate (hydrous and/oranhydrous) absorption features are ubiquitous in the CCs and R chondrites we have examined. Combininginformation on these features along with albedo and spectral slopes allows reasonable inferences to bemade concerning their uniqueness. Reflectance spectra of Coolidge show contributions from both olivineand Fe oxyhydroxides (from terrestrial weathering), and its high reflectance and mafic silicate banddepths are consistent with a petrologic grade >3 and inconsistent with CVs. The CC nature of the Cum-berland Falls inclusions from spectral analysis is inconclusive, but they do exhibit spectral features con-sistent with their overall mineralogy. DaG 430, which has petrologic characteristics of both CV and CKchondrites, has a spectrum that is not fully consistent with either group. The spectrum of EET 96029 isconsistent with some, but not all CM2 chondrites. GRO 95566, a meteorite with some affinities toCM2s, most resembles the Renazzo CR2 chondrite, consistent with their similar mineralogies, and itsspectral properties can be related to its major mineralogic characteristics. Spectra of Kaidun are mostconsistent with CR chondrites, which form the bulk of this meteorite. The reflectance spectrum of MCY92005 is consistent with its recent classification as a CM2 chondrite. The R3 chondrite MET 01149 sharesmany characteristics with CKs, but differs in terms of its slightly red slope and 2 lm region absorptionfeature. The combination of high reflectance, deep 1 lm band and, to a lesser extent, slightly red slopeand weak 2 lm region absorption band, distinguishes PRE 95404 from CV3s, to which it was initiallyassigned. The LAP 04840 R6 spectrum is dominated by olivine, consistent with a petrologic grade >3.Its reflectance is somewhat lower than for the R3 chondrites, and falls within the range of many CCs.Its most characteristic feature is the metal–OH absorption bands in the 2.3 lm region. Analysis andassignment of PCA 91467 (CH3) is complicated by the presence of terrestrial weathering products. Itsred spectral slope is consistent with its high metal content. Reflectance spectra of the howardite PRA04401, which contains �40% CM2-like inclusions, is dominated by the howardite’s pyroxene absorptionbands, and expected CM2-type absorption bands near 0.7 and 1.1 lm are not seen. The CC xenoliths doreduce overall reflectance and pyroxene absorption band depths significantly, and probably add an over-all red slope, when compared to inclusion-free howardites. QUE 99038, which has been linked to CM2,CO, or CR chondrites is not spectrally consistent with any of these groups. The 2 lm band, high overallreflectance, and dominant olivine absorption band are all generally inconsistent with CM2 and CR2–3chondrites. It resembles the CO3 chondrite ALH 77003 in the 1 lm region, but differs in the 2 lm region.The red-sloped, nearly featureless spectrum of Tagish Lake is unique among carbonaceous chondrites. Itprobably arises from the highly aromatic nature of the organic component and its intimate associationwith the phyllosilicate-rich matrix, which makes up a high proportion of this meteorite. Our results sug-gest that the meteorites included in this study can usually be determined to be either unique or to beplaced with a reasonable degree of confidence into established CC groups. Our analysis has also provided

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utis), pierre.hudon@mcgill.ca (P. Hudon), takahiro_hiroi@brown.edu (T. Hiroi), gaffey@space.edu (M.J. Gaffey).ials Engineering, McGill University, 3610 rue Université, Montreal, QC, Canada H3A 2B2.

Table 1Petrographic characteristics of

Group Chondruleabundance (vo

CI �1CM 20CR 50–60CO 48CV 45CK 15CH �70

E.A. Cloutis et al. / Icarus 221 (2012) 984–1001 985

insights into the degree to which spectral analysis can be used for characterization, the spectral featuresthat can be used for characterization, and their limitations.

� 2012 Elsevier Inc. All rights reserved.

1. Introduction

Carbonaceous chondrites (CCs) have been the subject of manyspectral reflectance studies because they are an important groupof meteorites for understanding the origin and evolution of the So-lar System. CCs include members, subgroups/grouplets and indi-vidual members that exhibit different degrees of aqueous and/orthermal alteration, but are generally characterized by an overalldark appearance. They are of astrobiological importance becausesome of their carbon-bearing phases are organic in nature and in-clude many biological precursor molecules (e.g., Nagy, 1975). Theymay also have been an important source of water for the proto-Earth (e.g., Chyba and Sagan, 1992; Morbidelli et al., 2000; Marty,2012; Trigo-Rodriguez and Martin-Torres, 2012).

We have undertaken a spectral reflectance study of CCs todetermine their range of spectral variability, to search for spectralsimilarities or differences between CC classes, to identify absorp-tion features or other spectral properties that are diagnostic of con-stituent phases, to better elucidate the relationships between CCmineralogy, structure, and spectra, and to inform the search forCC parent bodies.

This is the eighth paper in a comprehensive examination of thespectral reflectance properties of CCs. Previous papers in this serieshave dealt with the largest and most agreed-upon CC groups: CI,CM, CR, CO, CV, CK, as well as a group of CCs that exhibit evidenceof aqueous alteration followed by thermal metamorphism (Cloutiset al., 2011a,b, 2012a,b,c,d,e). In addition to these main groups,there exist a number of smaller grouplets and individual CCs thatdo not easily fit into existing classification schemes, and theseare the subject of the current paper. It should be noted that ouranalysis of ‘‘other’’ meteorites is by no means complete, as carbo-naceous or carbon-rich clasts are known to exist in many meteoritetypes (e.g., Bunch and Rajan, 1988; Rubin et al., 2005).

2. Carbonaceous chondrite classifications

The criteria used to define CC classes were discussed in Cloutiset al. (2011a), and are briefly reviewed here. CCs as a group werefirst defined by Mason (1962) as ‘‘stony meteorites characterizedby the presence of an appreciable amount of carbonaceous mate-rial other than free carbon (diamond and graphite)’’. In his classifi-cation, petrologic type 1 CCs are made up predominantly of largelyamorphous hydrated magnesium-iron silicate, hydrated magne-sium sulfate, and magnetite. Type 2 CCs consist largely of a serpen-tine groundmass impregnated with carbonaceous materialenclosing variable amounts of olivine and minor enstatite in theform of chondrules. Type 3 CCs consist in large part (�70%) of oliv-ine with minor amounts of pyroxene (5–10%), feldspar (5–10%),

C-chondrite groups. Source: Brearle

l.%)Matrixabundance(vol.%)

Refraabun

>99 �170 530–50 0.534 1340 1075 45 0.1

magnetite (�5%), and troilite (�6%); Fe–Ni metal may be presentin accessory amounts (Mason, 1962).

Newer methods that have been developed for discriminatingCCs from other types of meteorites are more composition-based,and involve elemental ratios, bulk composition, and oxygen isoto-pic ratios (Table 1; e.g., van Schmus and Wood, 1967; van Schmusand Hayes, 1974; Wasson, 1974, 1985; McSween, 1979; Dodd,1981). Compositional parameters that are useful for discriminatingdifferent CC groups and that may also translate into measurablespectral differences include iron oxidation state (oxidation increas-ing in the general sequence: CH(?) < CR < CV < CO < CK < CM < CI(Brearley and Jones, 1998), water content, and abundance of re-duced carbon (Roy-Poulsen et al., 1981). Recent summaries ofmeteorite classifications can be found in Weisberg et al. (2006)and Brearley (2006).

Petrologic criteria such as chondrule size, texture, and matrixabundance may not be useful for discriminating different CC par-ent bodies, as textures would be largely destroyed during regolithevolution. However, other discriminating criteria may persist;these include the higher content of dark matrix material, lowerbulk Fe, and �2 times more C and H2O in CVs than COs (van Sch-mus, 1969; van Schmus and Hayes, 1974; McSween, 1977a); lowermafic silicate Fe content and higher metal contents in CRs thanother CCs (Bischoff et al., 1993); and higher abundance of refrac-tory inclusions in COs and CVs as compared to other CCs (Brearleyand Jones, 1998). There are also correlations between organic mat-ter (C, H, N abundances) and clay contents with extent of pre-terrestrial aqueous alteration (Pearson et al., 2001). As with previ-ous papers in this series, we focus our analysis on powdered CCreflectance spectra.

In this paper, we have examined CCs that do not easily fit intoexisting classification schemes, members of grouplets for whichonly one to a few spectra exist, polymict CCs, CC-type inclusionsin other meteorites, and R chondrites. We use available mineral-ogic information for these samples in our analysis of their reflec-tance spectra and compare them, when appropriate, to spectra ofother CC groups or meteorites for which possible linkages exist.

3. Experimental procedure

The meteorites included in this study are described in Table 2.Our spectral data base incorporates existing spectra from the RE-LAB data base (http://www.planetary.brown.edu/relab/), many ofwhich have not been compared or analyzed in detail, reflectancespectra from other sources (Johnson and Fanale, 1973; Gaffey,1974, 1976), and new spectra acquired for this study that havebeen measured at the NASA RELAB Facility at Brown University

y and Jones (1998).

ctory inclusiondance (vol.%)

Metalabundance(vol.%)

Chondrule meandiameter (mm)

0 –0.1 0.35–8 0.71–5 0.150–5 1.0<0.01 0.720 0.02

Table 2Carbonaceous chondrite reflectance spectra included in this study. Sources of data: (1) Gaffey (1974) – 2 spectra; one digitized spectrum available through RELAB archive. (2)Johnson and Fanale (1973). (3) PSF – this study, duplicate spectra acquired.

Meteorite Type/description Grain size RELAB File ID Source of dataa

Coolidge C4 ungroupedCV affinities <150 lm mgp126 1

<74 lm 274–147 lm 2147–495 lm 2

Cumberland Fallsb Aubrite <74 lm 3>74 lm 3

DaG 430 C3-ungroupedCK, CV affinities <125 lm c1mp127

EET 96029 C2CM affinities <125 lm c1mp115

GRO 95566 C2-ungroupedCM2 affinities <125 lm c1mp60

Kaidun Polymict brecciac <45 lm c1ma7345–100 lm c1ma74100–250 lm c1ma75>250 lm c1ma76<125 lm c1mb98

MCY 92500 C2-unassigned probable CM2 <125 lm c1mp48MET 01149 R3 <75 lm c1ph45PCA 91467 CH3 <75 lm c1ph49PRA 04401d Howardite:

CM xenolith-bearing <45 lm 345–90 lm 390–250 lm 3

PRE 95404 R3 or CV3 <125 lm c1mt47QUE 99038 C2-ungrouped

CM/CR affinities <75 lm c1ph52Tagish Lake C2-unique

CM2/CR2/CI1 affinities <125 lm c2mt11e

<125 lm c2mt12f

6125 lm c1mt25l0g

a For spectra acquired at facility other than RELAB.b Xenolithic carbonaceous chondritic inclusions (whole rock spectra also measured).c Includes lithologies classified as C-ungrouped, CR, EH3–5, CV3, CM1–2, R, C1-ungrouped, and C2-ungrouped.d Contains �40 vol.% carbonaceous chondrite inclusions; whole rock spectra measured.e ET01-B subsample.f PMO 5c subsample.g Tagish7 subsample, <125 lm powder pressed into pellet for laser irradiation.

986 E.A. Cloutis et al. / Icarus 221 (2012) 984–1001

and the Planetary Spectrophotometer Facility at the University ofWinnipeg. Our analysis is focused on the 0.3–2.5 lm interval.

The reflectance spectra subjected to detailed analysis that weremeasured at the NASA-supported RELAB facility were acquired ati = 30� and e = 0� in bidirectional reflectance mode relative to halonfor the �0.3–2.5 lm region at 5 nm intervals, and corrected forminor irregularities in halon’s absolute reflectance in the 2.0–2.5 lm region. Details of the RELAB facility are available on theRELAB web site (http://www.planetary.brown.edu/relab/). Reflec-tance spectra measured at the University of Winnipeg PlanetarySpectrophotometer Facility (PSF) were acquired with an ASDFieldSpec Pro HR spectrometer from 0.35 to 2.5 lm at i = 30� ande = 0� relative to Spectralon� and corrected for minor reflectanceirregularities in the 2.0–2.5 lm region as well as detector offsetsat 1.00 and 1.83 lm. Details of PSF are available on the PSF web site(http://psf.uwinnipeg.ca). Spectra acquired at the PSF were mea-sured with a lampblack-coated aluminum mask (with a 5 mmdiameter central hole) placed over the samples and Spectralonstandard. Use of this mask was required as the sample did notalways fill the full field of view of the spectrometer.

Band minima wavelength positions were largely determinedusing visual criteria, supplemented by fitting horizontal chords atvarious positions across an absorption band and determining themid-point, and then averaging the midpoints or projecting themidpoints to the band minimum. This latter approach is most use-ful for noisy data and weak absorption bands. Absorption banddepths were calculated using Eq. (32) of Clark and Roush (1984)

after fitting a straight line continuum tangent to the spectrum oneither side of an absorption feature of interest. Band centers werecalculated the same way as band minima after continuum removal.The RELAB and PSF reflectance spectra discussed in this paper areprovided as an online Supplementary material.

4. Results

This study includes a diverse suite of meteorites that are eitherunclassified or of uncertain affinity for a variety of reasons. Some ofthe ungrouped meteorites included in this study may be membersof established groups, but have been insufficiently studied fordefinitive classification. Where appropriate, we have groupedsome meteorites together in our discussion.

4.1. Coolidge (C4-ungrouped; affinities to CV)

Coolidge is widely considered to be a C4 chondrite, with affini-ties to the CV group (CVR subgroup). Optical point counting gives67.4 vol.% chondrules and chondrule fragments, 4.0 vol.% AOIs,2.5 vol.% CAIs, a trace amount of lithic and mineral fragments,17.6 vol.% matrix, 3.7 vol.% metal, 2.6 vol.% sulfides, 3.4 vol.% mag-netite, and 1.8 vol.% hematite intimately intergrown with the mag-netite (McSween, 1977b). Noguchi (1994) describes Coolidge asconsisting of chondrules, AOIs, CAIs, metal and sulfide grains, iso-lated silicate minerals, and fine-grained matrix composed mostly

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of fragmental olivine (Fa�20–30) and minor pyroxene, which islikely chondrule fragments, and abundant Fe–Ni-metal and sul-fides (Noguchi, 1994). Chondrule olivines cluster around Fa14

(van Schmus, 1969; McSween, 1977b; Scott and Taylor, 1985;Noguchi, 1994). Low-Ca pyroxene is somewhat heterogeneous(Fs3–15; average Fs11Wo2.1) (McSween, 1977a,b; Noguchi, 1994).Opaque phases are largely kamacite and troilite (Scott and Taylor,1985). Fe–Ni-metal and troilite are present in chondrules (Noguchi,1994). In contrast to McSween (1977b), Fisher and Burns (1991)found that Coolidge contains no magnetite by Mössbauer spectros-copy, but does contain Fe oxyhydroxides resulting from terrestrialweathering. CAIs are very Fe-rich in comparison to CV CAIs(McSween, 1977b). Bulk C content is 0.01 wt.% (Pearson et al.,2006) or 0.19 wt.% (Jarosewich, 1990). It was classified as subtypeCV3.8 by Guimon et al. (1995).

Coolidge is spectrally anomalous in light of its mineralogy(Fig. 1). It is characterized by a steep reflectance rise in the0.5 lm region, a broad region of absorption longward of 0.75 lm,with a weak olivine absorption feature near 1 lm, and no well-de-fined pyroxene absorption feature near 1.9 lm. The two Coolidgespectra measured by Gaffey (1974), and from which the currentspectrum is derived, are nearly identical. The Coolidge spectrameasured by Johnson and Fanale (1973) also show a broad regionof absorption beyond �0.75 lm. Both the Gaffey (1974) and John-son and Fanale (1973) spectra show evidence of an olivine absorp-tion feature: a broad absorption band in the 1 lm region; only thecoarsest fraction spectra show a weak pyroxene band near 1.9 lmand the best evidence for a 1 lm region feature. The lack of well-defined mafic silicate absorption bands cannot be attributed to car-bonaceous compounds, as C content is <0.2 wt.% (Jarosewich, 1990;Pearson et al., 2006). The broad nature of the absorption featurebeyond 0.75 lm is consistent with a spectral contribution by mag-netite in addition to olivine. The terrestrial Fe oxyhydroxides areprobably responsible for the steep reflectance edge near 0.5 lmand the absorption band near 0.9 lm (Sherman et al., 1982).

Reflectance increases from �7% to �17% near 0.75 lm withdecreasing grain size (Johnson and Fanale, 1973). The increase inreflectance and an increasingly red slope with decreasing grain sizeare consistent with the behavior of other CCs (Johnson and Fanale,1973).

The continuum-removed spectrum of Coolidge (Fig. 1b) sug-gests spectral contributions from hematite/Fe oxyhydroxidesand/or orthopyroxene (feature near 0.9 lm) and olivine (featurenear 1.09 and 1.25 lm). Magnetite may account for the broadnessof the absorption feature near 1.0 lm.

We can compare Coolidge to other CVs, particularly the highermetamorphic grade ones and CVR chondrites. The highest meta-morphic grade CV is likely Allende (CV > 3.6; Bonal et al., 2006).Multiple spectra of Allende are available. Compared to Coolidge(Fig. 1c), they are darker and more red-sloped, and do not exhibitthe bow-shaped spectrum of Coolidge beyond 0.75 lm. The differ-ence in reflectance may be a function of aggregation of opaqueswith increasing thermal metamorphism, as Allende has a higherC content than Coolidge (0.27–0.39 wt.% versus 0.01–0.19 wt.%;Halbout et al., 1986; Jarosewich, 1990; Pearson et al., 2006), orthe terrestrially-produced Fe oxyhydroxides in Coolidge. Allendealso contains magnetite (1.2 vol.%; McSween, 1977b).

The 1 lm region absorption feature of Coolidge is likely real, asit also appears in the Johnson and Fanale (1973) Coolidge spectra.However, we suspect that this feature in the Allende spectrum maybe an artifact, as it only appears in the Gaffey (1974) Allende spec-trum – the other RELAB Allende spectra are dominated by olivine(Fig. 1d).

When Coolidge is compared to available CVR spectra (Fig. 1e),such as Leoville and Vigarano (both CVR 3.1–3.4; Bonal et al.,2006), the CVs are again darker than Coolidge, but more similar

in terms of overall slope (neutral to blue) and position of localmaxima near 0.75 lm. The continuum-removed spectra (Fig. 1f)are diverse. The Gaffey (1974) Leoville and Vigarano spectra bothshow an apparent absorption feature near 0.9 lm (like Coolidge)while the RELAB and PSF Vigarano and Leoville spectra do not.

Coolidge can also be compared to laboratory heated samples ofAllende (Fig. 1g). With increasing temperature (above �900 �C), Al-lende reflectance systematically increases, likely due to loss/agglomeration of opaques, and mafic silicate absorption bands be-come more apparent. Pre-existing poorly crystalline or amorphoussilicates are gradually converted to more crystalline forms. A 2 lmregion pyroxene band becomes more apparent with increasingtemperature, although this is likely due to the loss of opaquesrather than formation of pyroxene from other phases, as the1 lm region absorption band does not show a shift toward thepyroxene field (Fig. 1h).

The data collectively suggest that Coolidge has a spectrum withcontributions from both terrestrial Fe oxyhydroxides and olivine.The higher overall reflectance of Coolidge is consistent with thetrend found for other CCs, where increasing reflectance is associ-ated with increasing thermal metamorphism. The cause of thebow-shaped spectrum of Coolidge is not obvious, but is consistentwith magnetite. Spectrally, Coolidge differs in many respects fromthe available CV3.0–3.6 spectra, but differences in mafic silicatebands suggests that Coolidge’s spectrum is consistent with ther-mally metamorphosed CVs.

4.2. Cumberland Falls chondritic inclusions

Cumberland Falls is an enstatite achondrite (aubrite) that con-tains a number of black inclusions scattered heterogeneouslythroughout this meteorite (Neal and Lipschutz, 1981). Theseinclusions are of low petrologic type (63; Neal and Lipschutz,1981). An inclusion studied by Binns (1969) contained brokenand intact chondrules up to 1 mm in diameter in a brownish iso-tropic glassy to turbid gray groundmass, and occasional raggedmetal grains. He classified the inclusion as a primitive chondritewith possible affinities to LL chondrites. Major inclusion phasesinclude olivine, pyroxene (Low-Ca, diopside, and jadeite), plagio-clase feldspar, Fe–Ni metal, schriebersite, troilite, and other raresulfides (Neal and Lipschutz, 1981). Olivine and pyroxene arethe most common phases and both are low-Fe: most olivine isclose to pure forsterite and most pyroxene is Fs<7. The inclusionswere shocked during incorporation into the aubrite parent body(Neal and Lipschutz, 1981). We have included this material inthe current paper because of the black appearance of theinclusions but note that trace element data does not match CCs(Verkouteren and Lipschutz, 1983).

Reflectance spectra of the Cumberland Falls host and inclu-sions are shown in Fig. 2a and b. The unsorted powdered sampleof Cumberland Falls is strongly blue-sloped with 22.5% reflec-tance at 0.56 lm. This relatively high reflectance is consistentwith aubrites (Burbine et al., 2002). It also has a weak absorp-tion band near 0.9 lm, attributable to small amounts of low-Fe2+-bearing pyroxene in aubrites (Watters and Prinz, 1979); asecond expected absorption band near 1.9 lm is overprintedby likely water-bearing alteration phases. The inclusions havereflectance of 6.5–8.5% at 0.56 lm, consistent with values forCCs. The finer-grained fraction is brighter and less red-slopedthan the coarser fraction; this difference in slope is not consis-tent with how CC spectra vary with grain size as determinedby Johnson and Fanale (1973). The continuum-removed spectra(Fig. 2c) show a number of absorption features. Pyroxene ap-pears to be spectrally dominant – its wavelength position(0.93–0.95 lm) suggests contributions from phases besideslow-Ca pyroxene. Jadeite spectral contributions are suggested

Fig. 1. (a) Reflectance spectrum of a <150 lm powder of the Coolidge C4 chondrite measured by Gaffey (1974) using an integrating sphere and digitized by RELAB. (b)Continuum-removed spectrum from (a). (c) Coolidge versus various RELAB spectra of Allende. (d) Continuum-removed spectra from (c). (e) Coolidge versus CVR spectra fromRELAB (Vigarano), Gaffey (1974; Leoville (IS)), and PSF (Leoville 30/0). IS = integrating sphere spectrum). (f) Continuum-removed spectra from (e). (g) Coolidge spectrumversus RELAB spectra of the Allende CV3 heated to different temperatures. (h) Continuum-removed spectra from (g). Linear vertical offsets applied to some of the continuum-removed spectra for clarity are indicated (f and h).

988 E.A. Cloutis et al. / Icarus 221 (2012) 984–1001

by the absorption features near 1.10–1.15 lm, and a flattening ofthe spectral slope in the 0.7 lm region; jadeite can also contrib-ute to the 0.9 lm region feature. The 1.10–1.15 lm feature couldalso be attributed to phyllosilicates, although phyllosilicates havenot been identified in Cumberland Falls inclusions. Magnetitecould also account for the 1.10–1.15 lm feature. Spectral contri-butions by olivine are suggested by the bands/inflections near1.05 lm and 1.3 lm. The absorption feature near 1.35 lm islikely due to some hydrated phase; this may be due to terrestrialweathering, as native phyllosilicates have not been noted inCumberland Falls inclusions (Neal and Lipschutz, 1981). Fe3+-bearing weathering products could also account, in part, forthe 0.9 lm absorption feature.

4.3. DaG 430 (C3-ungrouped; affinities to CK, CV)

This meteorite has been classified as a C3 ungrouped chondritewith olivine and pyroxene compositions of Fa0.5–30.1 (averageFa20.7) and Fs1.1–20.6 (average Fs7.2), respectively (Grossman,1999). It exhibits metal grains in thin section (Grossman, 1999).It may be paired with DaG 055, 056, and 429; the followingdescription relates to DaG 055. The chondrules and mineral frag-ments consist of unequilibrated olivines (Fa0.4–32; mean Fa14.9)and pyroxene (Fs0.6–6; mean Fs2.6), while the matrix olivine ishighly equilibrated (Fa30–31) (Weber et al., 1996). This suggests apetrologic subtype lower than 3.5 (Weber et al., 1996). Theunequilibrated lithic mafic silicates and equilibrated matrix olivine

Fig. 1. (continued)

Fig. 2. (a) PSF spectra of an unsorted powder of the Cumberland Falls aubrite and a concentrate of chondritic inclusions for two grain sizes. (b) Same as (b) showing details ofthe inclusion spectra. (c) Continuum-removed spectra from (b). Linear vertical offset applied to one of the continuum-removed spectra for clarity is indicated.

E.A. Cloutis et al. / Icarus 221 (2012) 984–1001 989

compositions are similar to CK < 3.5 chondrites (Weber et al.,1996). It also has low modal abundance of CAIs and AOIs, similarto CK chondrites (Weber et al., 1996). Its chondrule size and matrixtexture are similar to CV chondrites, while its oxygen isotopes fallbetween the CV and CK groups (Weber et al., 1996).

Spectrally, DaG 430 (Fig. 3a) shows well-defined mafic silicateabsorption bands, including contributions from olivine (band near1.05 lm and inflections near 0.85 and 1.25 lm), and low-Ca pyrox-ene (inflection near 0.9 lm and band near 1.95 lm). Even thoughCAI abundances are low (Weber et al., 1996), CAI spinel may be

contributing to the suppressed rise in reflectance longward of�2.1 lm, which would be expected if only pyroxene was contrib-uting to this spectral region.

In comparison to the less equilibrated CV and CK chondrites,DaG 430 has similar overall reflectance and 1 lm region absorp-tion feature to MET 01149 (discussed below). The 2 lm region ofDaG 430 shows a greater contribution from pyroxene and spinelthan MET 01149. The CK4 chondrites are less like DaG 430, exhib-iting a 1 lm olivine-like absorption feature, but a weak or non-existent 2 lm feature (Cloutis et al., 2012e).

Fig. 3. (a) RELAB reflectance spectra of the MET 01149 R3 chondrite and DaG 430ungrouped C3 chondrites. (b) DaG430 and RELAB CV3 chondrite spectra.

Fig. 4. (a) RELAB spectra of the EET 96029 CM2 chondrite and ALH 84033 andMurchison CM2 chondrites. (b) Continuum-removed spectra from (a). Linearvertical offsets applied to some of the continuum-removed spectra for clarity areindicated.

990 E.A. Cloutis et al. / Icarus 221 (2012) 984–1001

Some CV3 chondrite spectra also show similarities to DaG 430(Fig. 3b). Similar-sized CV powder spectra are uniformly darkerthan DaG 430 (Cloutis et al., 2012d), but some have similar spectralfeatures to DaG 430, in particular their 1 lm region absorption fea-tures have similar position and shape, the 2 lm region also showscontributions by pyroxene and Fe2+-bearing spinels, and overallslopes are also similar. These data suggest that, at least spectrally,DaG 430 is most similar to CV3 rather than CK4 or R3 spectra.

4.4. EET 96029 (C2; affinity to CM)

EET 96029 was described as having a black interior with smallwhite inclusions (McBride and McCoy, 1998). It contains numeroussmall chondrules, larger CAIs, and mineral fragments in a blackmatrix; trace amounts of metal and troilite are present (McBrideand McCoy, 1998). The matrix appears to consist of serpentine;olivine composition ranges from Fa0 to Fa39, with most Fa0–2, andpyroxene ranges from Fs2 to Fs5, leading to a classification as aC2 chondrite (McBride and McCoy, 1998). It contains P-bearing sul-fides, like other CM chondrites (Nazarov et al., 2009). It was re-cently reclassified as CM2 (Righter, 2010).

EET 96029 differs from most CM2 chondrites in not exhibiting aprominent 0.75 lm region Fe2+–Fe3+ phyllosilicate charge transferband; however a few CM2s also do not exhibit this band (Fig. 4a).In particular one spectrum of Murchison (shown in Fig. 4a) andALH 84033 have some features in common with EET 96029; i.e.,similar spectral shape, overall reflectance, spectral slope, lack of0.7 lm absorption feature, and local reflectance maximum near0.8 lm. Murchison, like many other CM2s, show spectral variabil-ity, and hence not all Murchison spectra match EET 96029 (Cloutis

et al., 2011b). The continuum-removed spectra (Fig. 4b) show ex-pected variability. The EET 96029 spectrum shows evidence of oliv-ine (1.25 lm absorption feature) and Fe2+-bearing serpentine (0.9and 1.1 lm absorption features). The broad 1 lm region absorptionfeature of ALH 84033 also suggests contributions from olivine andserpentine. The shape of the continuum-removed Murchison spec-trum suggests a larger contribution from olivine (band center near1.08 lm) than serpentine. The spectral shape, slope, absorptionfeatures and overall reflectance of EET 96029 are all consistentwith the spectral properties of CM2s and indicate contributionsfrom both serpentine and olivine.

4.5. GRO 95566 (CM2 or C2-ungrouped)

GRO 95566 was recently reclassified from a C2 to a C2-un-grouped chondrite (Righter, 2008). Some chondrules are rusty; itcontains numerous small chondrules, some irregular aggregates,and many small silicate grains in a black matrix; trace amountsof metal and troilite are present as minute grains (McBride andMason, 1997b). The silicate grains are almost entirely olivine nearFa0, with a few more Fe-rich grains up to Fa35 (Choe et al., 2010); alittle pyroxene of Fs2–4 is also present (Choe et al., 2010), and thematrix appears to consist largely of Fe-rich serpentine (McBrideand Mason, 1997b). Chondrule mesostatis has been altered tophyllosilicates (Choe et al., 2010). Clayton and Mayeda (1999)determined that GRO 95566 appears to be a CM2 chondrite, buthas exceptional oxygen isotope composition. In comparison toCM2 chondrites, GRO 95566 is less altered (Choe et al., 2010).

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The spectrum of GRO 95566 is consistent with a carbonaceousmeteorite containing Fe-poor mafic silicates (Fig. 5a): reflectanceis �5% in the visible region, and absorption bands are weak. Min-eralogically, it is most similar to CR chondrites in terms of lowFe-olivine and presence of serpentine. Spectrally, it is most similarto the Renazzo CR2 fall in overall reflectance, spectral shape andslope, and a weak 1 lm region absorption feature. It is much darkerthan other CR2s, which may reflect differences in opaque abun-dances and distribution.

The weathering grade of GRO 95566 is A/Be, similar to otherAntarctic CR2s (Cloutis et al., 2012a). However, we believe thateven low weathering grades can add spectral features due to ter-restrially-produced Fe oxyhydroxides, as their mafic silicates areFe-poor and consequently have shallow mafic silicate absorptionbands (Cloutis et al., 2012a). The continuum-removed spectra(Fig. 5b) show that Renazzo is most similar to GRO 95566 in termsof having a shallow 1 lm region absorption band with probablycontributions from olivine (1.05 and 1.25 lm) and serpentine(0.9 and 1.1 lm). It differs from the other CR2 spectra, which havea narrower 1 lm region absorption feature and which have strongspectral contributions near 0.9 lm from Fe oxyhydroxides. Overall,GRO 95566 resembles the Renazzo CR2 chondrite, which is ex-pected given similar mineralogy – particularly low-Fe olivinechondrules and mineral fragments and serpentine-dominatedgroundmass. This reiterates the fact that CC reflectance spectracan be variable and that silicate mineralogy can be roughly con-strained from, in particular, the 1 lm region.

Fig. 5. (a) RELAB reflectance spectra of the GRO 95566 C2-ungrouped chondrite anda number of CR2 chondrites. (b) Continuum-removed spectra from (a). Linearvertical offsets applied to some of the continuum-removed spectra for clarity areindicated.

4.6. Kaidun (C-ungrouped, polymict breccia; predominantly CR withdiverse xenoliths)

This meteorite is a complex breccia that appears to be mainlyCR chondrite but containing clasts of several other carbonaceouschondrites (CV3, CM1-2), ordinary chondrites, and enstatite chon-drites (EL3, EH3–5) (Ivanov, 1989; Krot et al., 2002; Kurat et al.,2004), as well as other unique lithologies (C1 and C2 type, Ca-richachondrite, alkaline-enriched clasts) and impact melts (Zolenskyand Ivanov, 2003). In the CR portion of the meteorite, matrix com-prises �70 vol.% and is composed mainly of phyllosilicates (pre-dominantly smectite and serpentine), magnetite, carbonates,oxysulfides, and carbonaceous material (Ivanov, 1989; Goldenet al., 1994). Some inclusions are composed of olivine (Fa0.3–38.4)and low-Ca pyroxene (Fs0.2–20Wo0.1–4.5) (Ivanov, 1989). While itshares some chemical affinities with CR chondrites, it does not dis-play recognizable CR petrologic features (Zolensky and Ivanov,2003).

Multiple spectra are available for Kaidun (Fig. 6a). The increas-ing grain size series exhibits decreasing reflectance and bluer over-all slope, consistent with other CCs (Johnson and Fanale, 1973). The<125 lm fraction spectrum has similar slope to the <45 lm spec-trum, but overall reflectance is �1% lower. The continuum-removed spectra (Fig. 6b) exhibit a number of absorption featuresin the 1 lm region, most noticeably in the larger grain size spectra.The relative lack of well-resolved absorption bands in thefine-grained spectra is consistent with the behavior exhibited bythe CR2 chondrite Renazzo (Fig. 5a and b). The coarser grain size

Fig. 6. (a) RELAB reflectance spectra of various size fractions of the Kaidun polymictbrecciated meteorite. (b) Continuum-removed spectra from (a). Linear verticaloffsets applied to some of the continuum-removed spectra for clarity are indicated.

Fig. 7. (a) RELAB reflectance spectra of the MCY 92500 CM2 chondrite and anumber of other CM2 chondrites. (b) Continuum-removed spectra from (a). Linearvertical offsets applied to some of the continuum-removed spectra for clarity areindicated.

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spectra show a broad absorption feature in the 1 lm region withprobable absorption bands near 0.7, 0.90–0.93, 1.0–1.1 lm, and1.25 lm. The 0.7 lm feature is consistent with the abundant ser-pentine in Kaidun, and indicates that it is an Fe2+–Fe3+-bearingvariety. The 0.90–0.93 lm feature is also consistent with serpen-tine, but could also be attributed to enstatite. The 1.0–1.1 lm fea-ture can be attributed to magnetite, olivine, and/or serpentine. The1.25 lm is uniquely attributable to olivine, which is present in CRchondrites. Overall, the fine-grained Kaidun spectra are consistentwith CR chondrites, largely due to the low overall reflectance andlack of strong silicate absorption bands. The larger grain size spec-tra show better evidence of the various silicate components andpossibly magnetite that comprise the bulk of Kaidun.

4.7. MCY 92500 (C2-unassigned; CM2)

This meteorite was classified as a C2 chondrite by Satterwhiteand Mason (1993). The interior matrix is fine-grained, medium todark gray, with abundant small white and gray inclusions and afew chondrules; oxidation is minor (Satterwhite and Mason,1993). A thin section shows chondrules, irregular aggregates andsmall mineral grains in a black matrix; the minerals are mostlyolivine with minor pyroxene (Satterwhite and Mason, 1993). Oliv-ine compositions are mostly close to Fa0 with occasional Fe-richgrains up to Fa42, and pyroxene composition ranges from Fs1

to Fs5; the matrix appears to be largely Fe-rich serpentine(Satterwhite and Mason, 1993). This meteorite was classified asnot thermally metamorphosed because it exhibits an absorptionfeature near 0.7 lm, and band shape and strength in the 3 lmregion is dissimilar to known thermally metamorphosed C chon-drites (Hiroi et al., 1997). It was more recently classified as aCM2 (Righter, 2010).

Its reflectance spectrum (Fig. 7a) is similar to many CM2 chon-drites in terms of all major spectral properties, such as overallreflectance, slope and 1 lm region absorption features. This isshown more clearly in Fig. 7b, where MCY 92500 and these CM2chondrites all exhibit a 0.7 lm Fe2+–Fe3+ charge transfer serpentineband, and 0.93 and 1.1 lm Fe2+ crystal field serpentine bands. Theexpected olivine absorption bands near 1.05 and 1.25 lm are notapparent, likely due to overlaps from the adjacent serpentinebands and the low olivine Fa content. The spectrum of MCY92005 is consistent with other CM2 spectra discussed in more de-tail in Cloutis et al. (2011b).

4.8. R chondrites: MET 01149 (R3), PRE 95404 (R3), and LAP 04840(R6)

MET 01149, PRE 95404, and LAP 04840 have been identified asR chondrites, and are discussed together here. MET 01149 was re-cently classified as an R chondrite on the basis of various petrologicand compositional criteria (Righter, 2010). The interior shows amedium-gray matrix with some gray and white clasts and chond-rules, and very little weathering (McBride et al., 2003). A thin sec-tion shows well-defined chondrules in a matrix of finer-grainedsilicates, magnetite and abundant sulfide, and it is extensivelyshocked (McBride et al., 2003). It contains 25 vol.% chondrules,7 vol.% opaques, 2 vol.% CAIs, and 66 vol.% matrix (Neff and Righter,2006). Silicates are heterogeneous: olivine is Fa2–39 with manygrains around Fa39 (McBride et al., 2003); Neff and Righter(2006) give olivine composition as �Fa37.

PRE 95404 was tentatively classified as a CV3 by McBride andMason (1997a), but it lacks the marked olivine composition peakat Fa0–1 commonly present in C3 chondrites. It was later reclassi-fied as an R3 chondrite (Imae and Zolensky, 2003; Righter, 2008).The interior is a gray crystalline mass with metal grains andlight-colored chondrules (McBride and Mason, 1997a). An interior

section shows numerous chondrules, chondrule fragments, irregu-lar aggregates and silicate grains in a black matrix which contains amoderate amount of Fe–Ni-metal and sulfide (McBride and Mason,1997a). Olivine composition is variable, Fa1–41, as is pyroxene, Fs7–

21; the matrix consist largely of olivine with composition aroundFa30 (McBride and Mason, 1997a). Imae and Zolensky (2003) iden-tified R3 and R4 clasts in PRE 95404. Olivine composition rangesfrom Fa5 to Fa40 in the R3 clast, but is clustered around Fa38–40 inthe R > 4 clast; low Ca and high Ca pyroxenes are both present, sul-fides consist of pyrrhotite and pentlandite and mainly occur asopaque chondrules, and no metals are present (Imae and Zolensky,2003).

R chondrites are characterized by highly oxidized (Fe-rich) oliv-ine, and are distinguished from CK chondrites (which are also oxi-dized) by the absence of magnetite (Imae and Zolensky, 2003).Olivine is the major component of R chondrites, with lesseramounts of plagioclase feldspar, pyroxene, and abundant (6–10 wt.%) pyrrhotite and pentlandite (Schulze et al., 1994; Isaet al., 2010). The chondrule/matrix ratio for R chondrites is lowestamong chondrites (Imae and Zolensky, 2003). CAIs and Fe–Ni me-tal are rare, and Fe3+-bearing spinels may be present (Rout andBischoff, 2008; Isa et al., 2010). Pyroxene abundance decreaseswith increasing metamorphism.

Reflectance spectra of MET 01149 and PRE 95404 are shown inFig. 8. Both spectra are characterized by high reflectance (15–19%at 0.56 lm), a well-defined olivine absorption band centered at1.06 lm, and an additional absorption feature in the 2.1 lm region.The 2 lm region absorption feature suggests contributions from

Fig. 8. RELAB reflectance spectra of the MET 01149 and PRE 95404 R3 chondrites. Fig. 9. PSF reflectance spectra of a bulk sample and sorted powder of the LAP 04840R6 chondrite.

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low-Ca pyroxene and/or Fe-bearing spinels as it is broad and cen-tered between �2.1 and 2.2 lm (Cloutis et al., 2004). These spectraare similar to Rumuruti, another R3 chondrite (Burbine et al.,2003).

Compared to CV chondrites, PRE 95404 is consistently brighterfor comparable size powder spectra. PRE 95404 is slightly red-sloped, as are a number of CVs (Cloutis et al., 2012d). PRE 95404and CV chondrites show a well-defined olivine absorption featurenear 1 lm. The 1 lm region band depth of PRE 95404 (16.3%) isgreater than CVs (<10%) and comparable to Allende heated to>1100 �C (Cloutis et al., 2012d). The combination of high reflec-tance, deep 1 lm band and, to a lesser extent, slightly red slopeand weak 2 lm region absorption band, distinguishes PRE 95404from CV3s.

LAP 04840 is an R6 chondrite. The interior is a fine grained crys-talline matrix with black and white crystalline inclusions, and noevidence of rusting or metal (McBride and McCoy, 2006). In thinsection, LAP 04840 is texturally heterogeneous, containing relictchondrules up to 1 mm, and 100–200 lm mineral grains andmicrocrystalline areas with 5–10 lm mafic silicate grains. It con-sists of FeO-rich olivine (Fa38), orthopyroxene (Fs30Wo1), and pla-gioclase feldspar (An7Or3). Hornblende comprises �15% of themeteorite, with composition (wt.%) of approximately 48% SiO2,3% Na2O, 6% Al2O3, 16.5% MgO, 11% FeO, 10% CaO and <0.5% TiO2,MnO and K2O, and no Cl. Opaque minerals include troilite, pent-landite and chromite. The presence of hornblende and biotite isconsistent with high temperature aqueous alteration at depth(Mikouchi et al., 2007). Other R6 chondrites do not contain horn-blende or biotite (Isa et al., 2010), suggesting that an influx ofwater was required for the formation of the hydrated phases(Mikouchi et al., 2007). Reflectance spectra of LAP 04840 andamphibole separates (Klima et al., 2007) indicate that identifyingthe presence of amphibole in LAP 04840 reflectance spectra below2.5 lm is difficult because it has a weak Fe3+–Fe2+ charge transferband, and the Fe2+ charge transfer band is overlapped by the stron-ger olivine Fe2+ charge transfer band. However, the amphibole sep-arate and the <125 lm whole rock spectra (Klima et al., 2007) doshow metal–OH combination bands in the 2.3–2.4 lm region thatcan be attributed to amphibole (Mustard et al., 1989).

Reflectance spectra of LAP 04840 measured at the PSF areshown in Fig. 9. They show similar behavior to the LAP 04840 spec-tra of Klima et al. (2007). Both the bulk and <250 lm spectra aredominated by olivine; the presence of hornblende/biotite is sug-gested by the weak absorption bands in the 2.3–2.4 lm region.Reflectance is somewhat lower than for the R3 chondrites, and fallswithin the range of many CCs. The most characteristic feature ofLAP 04840 is the metal–OH absorption bands in the 2.3 lm region.

4.9. PCA 91467 (CH3)

PCA 91467 has been identified as a CH3 chondrite. The interioris dark brown to black and fine-grained, with a few small inclu-sions and extensive weathering (Marlow et al., 1993). A thin sec-tion shows a few chondrules, abundant pyroxene grains and aconsiderable amount of Fe–Ni-metal; it is severely weathered withlimonitic staining (Marlow et al., 1993), although some portionsappear to be unweathered (Bischoff et al., 1994). Most of thepyroxene is close to Fs0, but ranges up to Fs16 (Marlow et al.,1993). It is metal-rich with only a few chondrules (Bischoff et al.,1994). CAI abundance is below 1 vol.%, and the most abundantcomponents are mineral and lithic fragments (Bischoff et al.,1994). A wide range of olivine (Fa1–58) and pyroxene (Fs1–46)compositions were found, but most are MgO-rich with peaks atFa1–4 (olivine) and Fs1–5 (pyroxene) (Bischoff et al., 1994). It con-tains carbon–silicate aggregates, Fe–Ni-metal grains and abundanthydrated materials (Sugiura, 2000); all of the fine-grained matrixseems to be hydrated to some degree, along with some evidenceof subsequent dehydration (Sugiura, 2000). Framboidal magnetiteis present, again suggesting hydration (Sugiura, 2000). It also con-tains xenolithic clasts (Zolensky et al., 2009).

CH chondrites are among the most primitive meteorites withinthe carbonaceous chondrite suite (Hezel et al., 2003). They contain�70 vol.% 20–90 lm-size chondrules and chondrule fragments,�20 vol.% Fe–Ni metal (among the highest metal abundance ofany C chondrite group), low Fe in the mafic silicates, low abun-dances of CAIs (<0.1–1 vol.%) and lack fine-grained interchondrulematrix (Krot et al., 2002, 2012; Hezel et al., 2003; Weisberg et al.,2006; Krot, 2008). Ferrous chondrules (Fe:(Fe + Mg) = 0.11–0.35)are also present (Krot et al., 2002). While CAIs are of low overallabundance, they are common because of their small size (Brearleyand Jones, 1998). The constituent CAI minerals are all more Fe-richon average than CAIs in CM and CV chondrites (Brearley and Jones,1998), and common phases include grossite (CaAl4O7) and melilite,with accessory hibonite, spinel and perovskite (Brearley and Jones,1998). CH chondrites contain completely hydrated matrix lumps(Krot et al., 2000) that contain magnetite, sulfides, and carbonatesset in a phyllosilicate matrix that is composed of serpentine andsaponite (Greshake et al., 2002). The phyllosilicates are Fe-rich(Fe/(Fe + Mg) = �0.62 (Greshake et al., 2002). ALH 85085 (a proba-ble CH chondrite) contains �10 vol.% obvious chondrules, 62 vol.%other silicate particles (�90% pyroxene of �Fs4 and 10% olivine ofmostly Fa0.5–2.8, �0.1 vol.% CAIs, 23 vol.% opaque minerals, and�4 vol.% CI clasts (Grossman et al., 1988). Another analysis ofALH 85085 gives 70 vol.% silicate fragments, 20 vol.% Fe–Ni metal,

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5 vol.% matrix lumps that are phyllosilicate-rich, 5 vol.% chond-rules, 0.4 vol.% troilite, and 0.1 vol.% magnetite (Scott, 1988). Thereare indications that CHs are related to CR and CB chondrites interms of at least their region of formation (Weisberg et al., 1995).

The reflectance spectrum of PCA 91467 is shown in Fig. 10a. PCA91467 is characterized by a red-sloped spectrum with 10% reflec-tance at 0.56 lm and 14% reflectance at the 0.8 lm peak. It exhibitstwo absorption features near 0.9 and 1.95 lm. The continuum-removed spectrum (Fig. 10b) shows a 3% deep absorption featurecentered near 0.93 lm. It appears to be asymmetric with ashallower long wavelength wing. This feature is consistent withlow-Ca pyroxene, although the band is located at slightly longerwavelengths than would be expected for low Fe-content low-Capyroxene (Cloutis and Gaffey, 1991). The shallow absorption fea-ture centered near 1.93 lm is also consistent with low-Ca pyrox-ene. The identification of abundant terrestrial weatheringproducts (limonitic staining; Marlow et al., 1993) and the steepreflectance dropoff shortward of �0.6 lm, suggests that the0.9 lm feature includes spectral contributions from terrestrialweathering products, particularly when coupled to the low Fs con-tent of the pyroxene. The 1.9 lm region absorption feature mayalso contain contributions from terrestrial weathering products,as well as the common hydrated silicates it contains (Sugiura,2000). The red slope of this meteorite is likely attributable to acombination of its abundant metal and terrestrially-produced Feoxyhydroxides. Given the composition of this meteorite, it seemslikely that PCA 91467 is a reasonable spectral analogue for CH3chondrites, but terrestrial weathering has likely led to an increasein spectral slope below 0.6 lm, and a deepening of the 0.9 and1.9 lm region absorption features. Its overall reflectance falls with-

Fig. 10. RELAB reflectance spectrum of the PCA 91467 CH3 chondrite. (b)Continuum-removed spectrum from (a).

in the range for most CCs. A reflectance spectrum of a chip of PCA91467 exhibits maximum reflectance of �12% at 0.3 lm (Trigo-Rodriguez, personal communication, 2012), suggestive of lessweathering products in his sample, reinforcing the observationthat weathering is heterogeneous in this meteorite.

4.10. PRA 04401 (howardite)

PRA 04401 is a howardite that contains �60% CM2 clasts(McBride et al., 2007; Herrin et al., 2010, 2011). The originaldescription of PRA 04401 is ‘‘a groundmass of comminuted pyrox-ene and plagioclase (up to 0.5 mm) with fine- to coarse-grainedbasaltic clasts ranging up to 5 mm’’ (McBride et al., 2007). Its orth-opyroxene is compositionally diverse (Fs16–60Wo1–3) and plagio-clase feldspar composition is An87–90 (McBride et al., 2007). Oursample of PRA 04401 contained �40% visible CM2 clasts, rangingin size up to �4 mm.

Fig. 11a shows reflectance spectra of PRA 04401 for differentgrain sizes and Fig. 11b shows the <45 lm fraction of PRA 04401compared to other <45 lm inclusion-free howardites. Comparisonof these spectra indicates that the CM2-type inclusions in PRA04401 cause reflectance to decrease. With increasing grain size,the PRA 04401 spectra become darker and more blue-sloped,consistent with the behavior of other CM2 spectra (Johnson andFanale, 1973; Cloutis et al., 2012b). However, expected CM2-typeabsorption bands, near 0.7, and 1.1 lm are not apparent in thePRA 04401 spectra, even given its high CM2 abundance. With thecurrent spectral data we are not able to ascertain the spectral prop-erties of the CM2 type inclusions, beyond the fact that they are

Fig. 11. (a) PSF reflectance spectra of different size fractions of the PRA 04401 – acarbonaceous chondrite xenolith-bearing howardite. (b) Reflectance spectra of<45 lm fractions of PRA 04401 and a number of other howardites.

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dark and probably red-sloped over the 0.8–2.5 lm interval. Thesespectra will be discussed in more detail in an upcoming paper.

4.11. QUE 99038 (C2-ungrouped; affinities to CM2, CO, CR)

The interior is charcoal gray with numerous chondrules andlight and dark gray crystalline material (McBride et al., 2001). Athin section shows a few small chondrules, mineral grains and CAIsset in a black matrix; rare metal and sulfide grains are present(McBride et al., 2001). Olivine compositions are Fa1–39, with manyFa0–3; the matrix consists predominantly of an Fe-rich serpentine,and it was classified initially as a CM2 chondrite (McBride et al.,2001). It is an aqueously altered chondrite, but differs from CMsbecause its chondrules are larger; they are closer to CR chondrulesin size (Huber et al., 2006; Choe et al., 2010). However, unlike CRchondrites, QUE 99038 contains little metal. Refractory lithophilesare close to the CO range (Huber et al., 2006). The anomalous bulkcomposition and other petrologic features led to its being classifiedas a devolatilized petrologic type 2 ungrouped chondrite by Huberet al. (2006) and Choe et al. (2010).

The spectrum of QUE 99038 is shown in Fig. 12a. It is unlikemost CM2 chondrites in terms of having higher reflectance and awell-defined 2 lm region absorption feature (Cloutis et al.,2012b). Superficially, it resembles some CO3 chondrites (e.g., ALH77003) in having a well-defined olivine-type absorption band,and a 2 lm region absorption feature. While the overall reflectanceof QUE 99038 is similar to COs, the 2 lm region absorption banddoes not resemble that of COs, whose spectra in this region showevidence of Fe2+-bearing spinel. The 2 lm region absorption band

Fig. 12. (a) RELAB reflectance spectra of the QUE 99038 C2-ungrouped chondriteand the ALH 77003 CO3 chondrite. (b) Linear vertical offset applied to one of thecontinuum-removed spectra for clarity is indicated.

center of QUE 99038 is near 1.98 lm, which is suggestive of pyrox-ene (whose presence in this meteorite is undocumented). The con-tinuum-removed 1 lm region (Fig. 12b) shows an absorptionfeature centered near 1.06 lm, and a prominent inflection near1.25 lm, both consistent with olivine. The presence of pyroxeneis also suggested by a weak inflection near 0.9 lm. The presenceof phyllosilicates (serpentine) likely accounts for the asymmetricappearance of the absorption feature near 1.1 lm, and may alsobe contributing to the weak inflection near 0.9 lm. The 2 lm band,high overall reflectance, and dominant olivine absorption band areall generally inconsistent with CM2 and CR2–3 chondrites, indicat-ing that QUE 99038 is spectrally and mineralogically distinct fromCM2 and CR2–3 chondrites. It again resembles the CO3 chondriteALH 77003 in the 1 lm region, but, as mentioned, differs in the2 lm region.

4.12. Tagish Lake (C2-unique; affinities to CM2, CR2, CI1)

4.12.1. DescriptionThe Tagish Lake carbonaceous chondrite, which fell in 2000

(Brown et al., 2000), was recognized as a new type of CC almostimmediately. It has at least four distinct lithologies: carbonate-poor, carbonate-rich, inclusion-poor magnetite- and sulfide-rich,and carbonate-rich, siderite-dominated (Bland et al., 2002;Zolensky et al., 2002; Izawa et al., 2010). Modal mineralogies fora number of subsamples are given in Tables 3 and 4. Overall, TagishLake is composed of abundant phyllosilicate-rich matrix (�80%),and lesser amounts of carbonates, olivine, sulfides, and magnetite,sparse CAIs, and aqueously-altered chondrules (Alexander et al.,2007).

The carbonate-poor lithology consists of fine- to coarse-grained,phyllosilicate-rich clasts, sparse altered chondrules, aggregates,sparse CAIs, grains of olivine, magnetite, Fe–Ni sulfides,phosphides, and rare carbonates (Zolensky et al., 2002). Thecarbonate-rich lithology is more depleted in CAIs, aggregates,fine-grained sulfides, and magnetite, the phyllosilicates are almostentirely saponite, and Fe–Mg–Ca–Mn carbonates are very abun-dant (Zolensky et al., 2002). Noguchi et al. (2002) described thetwo major lithologies as follows: the carbonate-rich matrix con-tains saponite, pyrrhotite, Mg-siderite, pentlandite, and magnetite,and the carbonate-poor matrix contains saponite, magnetite, pyr-rhotite, Mg-siderite, pentlandite, and calcite. Gypsum and talc havebeen found in inclusion-rich subsamples of Tagish Lake (Izawaet al., 2010).

4.12.2. Matrix and phyllosilicatesThe matrix consists of intergrown saponite and serpentine, Mg–

Fe carbonates, Fe–Ni sulfides (mostly pyrrhotite); magnetite andolivine are also present (Brown et al., 2000; Keller and Flynn,2001; Noguchi et al., 2001; Zolensky et al., 2002; Bland et al.,2004).The phyllosilicates are compositionally similar to Ivuna(CI1) and more Fe-rich than Orgueil and Alais (CI1) (Keller andFlynn, 2001). The phyllosilicates are Fe/(Fe + Mg) � 0.3 (Zolenskyet al., 2002).

Table 3Modal mineralogy of the Tagish Lake carbonaceous chondrite. Source: Bland et al.(2004).

Phase wt.% vol.%

Olivine (Fo100) 7.9 7.0Fe–Mg carbonate 14.4 11.7Pyrrhotite 8.5 5.3Pentlandite 0.6 0.3Magnetite 8.3 4.5Saponite–serpentine 60.3 71.2

Table 4Modal mineralogy of various lithologies in the Tagish Lake carbonaceous chondrite. Source: Izawa et al. (2010).

Phase Subsample

HG-42 (wt.%) HG-11 (wt.%) MM-38 (wt.%) MG-02 (wt.%) MM-02 (wt.%) PB-02 (wt.%) MM-63 (wt.%)

Saponite–serpentine 57 55 55 52 49 48 44Olivine 4 9 8 12 9 9 5Magnetite 13 9 12 13 8 6 17Siderite 5 4 5 9 11 24 13Calcite 63 5 63 63 63 63 63Dolomite n.d. n.d. n.d. 63 63 n.d. n.d.Pyrrhotite 10 16 10 13 18 13 17Pentlandite 63 63 63 63 63 63 63Gypsum 8 63 10 n.d. n.d. n.d. 63Talc 63 n.d. n.d. n.d. n.d. n.d. n.d.

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4.12.3. Carbon and carbonaceous phasesThe organic matter is closely associated with the phyllosilicates

(Pearson et al., 2002), with the bulk of the C present in intimateassociation with the matrix phyllosilicates (Pearson et al., 2002;Garvie and Buseck, 2004). Total carbon content has been measuredas 4.25 wt.% (Pearson et al., 2006), or 5.4 wt.%, with an estimated3.7 wt.% derived from carbonates, which is a higher proportionthan is usual in CI or CM chondrites (typically 0.2–0.5 wt.% C fromcarbonates) (Brown et al., 2000). The insoluble carbonaceous frac-tion appears to be composed largely of polyaromatic molecules(Zega et al., 2010) consisting of a few (�10) rings in a disorderedarrangement (Derenne et al., 2006), and are highly condensed(Gilmour et al., 2001). The insoluble organic matter has the highestaromaticity and lowest bulk H/C ratio of any petrologic type 1–2CC (Alexander et al., 2010). The fraction of aromatic carbon is0.79 (Cody et al., 2003). Organic C content is 2.00 wt.% (Alexanderet al., 2007). There are wide variations in many organic componentproperties between different lithologies of Tagish Lake that provideinsights into differences in parent body processing (Herd et al.,2010).

4.12.4. CarbonatesA variety of carbonates seem to exist in Tagish Lake, with rela-

tive abundances varying between the major lithologies. Differentsamples can contain Fe- and Ca-rich carbonates or just Fe-rich car-bonates (Blinova and Herd, 2010; Izawa et al., 2010). Brown et al.(2000) describe the carbonates as varying between siderite, mag-nesite, and calcite, with some containing up to 1% Mn. Dolomiteis the major carbonate in altered chondrules (Zolensky et al.,2002). Calcium carbonate is the most common carbonate in thecarbonate-poor lithology (Zolensky et al., 2002), but uncommoncompared to the carbonate-rich lithology, and it can contain someFe. According to Zolensky et al. (2002), Fe–Mg–Ca–Mn carbonatesare very common in the carbonate-rich lithology, but calcium car-bonate grains are rare, while the carbonates in the carbonate-richlithology seem to consist of calcium carbonate cores with Mg–Fe–Mn carbonate rims. Changes in carbonate mineralogy are indic-ative of differences in degree of aqueous alteration (Rubin et al.,2007).

4.12.5. Classification and comparison to other CCsAbundant phyllosilicates, sparse chondrules and common oliv-

ine grains in the matrix are consistent with petrographic grade 2(Gounelle et al., 2001). Tagish Lake has a matrix mineralogy similarto CR2 chondrites (Gounelle et al., 2001), while the presence of al-tered chondrules and CAIs, olivine composition, and relative abun-dance of sulfides are consistent with CM2 chondrites (Gounelleet al., 2001; Rubin et al., 2007). Isolated, unaltered olivine grainsand the anhydrous inclusions share similarities with CM meteor-ites, but Tagish Lake has been more extensively aqueously altered

than known CM chondrites (Simon and Grossman, 2003; Rubinet al., 2007).

4.12.6. Reflectance spectraA number of Tagish Lake samples have been spectrally charac-

terized (Hiroi et al., 2001a,b, 2003, 2004). Hiroi et al. (2001a) founda close spectral similarity to D asteroids, specifically 368 Haidea(Hiroi et al., 2001a,b), and to other T- and D-class asteroids (Hiroiet al., 2003). Spectra of Tagish Lake available for analysis, includingfresher (ET01b) and more weathered (PM05c) samples (Hiroi et al.,2001b). Fig. 13a shows that <125 lm powder spectra of these twosubsamples are very similar. A pressed powder has higher reflec-tance and is less red-sloped than loose powders. While the spectramay appear featureless, continuum removal in the 0.6–0.8 and0.8–1.5 lm region shows the presence of shallow (�1–2% deep)absorption features (Fig. 13b). A �1% deep band is located at0.7 lm, and is attributable to Fe3+–Fe2+ charge transfers in theabundant Fe-bearing serpentine; this phase also likely accountsfor the bands near 0.9 and 1.1 lm. These bands resemble thoseseen in other serpentine-bearing CCs, such as CMs (Cloutis et al.,2011b), but much suppressed. There are suggestions of contribu-tions by olivine near 1.25 lm, although this feature is not well ex-pressed; olivine is present but sparse in Tagish Lake. The overallreflectance of Tagish Lake is low, �2% at 0.56 lm, lower than thevalues for CMs (Cloutis et al., 2011b), and consistent with the or-ganic matter being intimately associated with the phyllosilicates(Pearson et al., 2002; Garvie and Buseck, 2004). Roush (2003)found that a number of phases in this meteorite contribute to itsspectrum. Possible contributions from the various carbonatesand/or serpentine in Tagish Lake are suggested by the weak, broadabsorption feature seen in the 2.3–2.4 lm region of the loose pow-der spectra.

The red-sloped, nearly featureless spectrum of Tagish Lake isunique among carbonaceous chondrites. It probably arises fromthe highly aromatic nature of the organic component, and its inti-mate association with the phyllosilicate-rich matrix, which makesup a high proportion of this meteorite, probably accounts for itsspectral characteristics (Cloutis, 2003).

5. Discussion

The most fruitful approach to analysis of ungrouped/unassignedCCs relies largely on analysis of spectrally active phases – i.e., thosephases that contribute absorption features to the CC spectra. We canuse the presence or absence of features, coupled to their approxi-mate wavelength positions as diagnostic determinations of CC min-eralogy. We also include properties such as shape of absorptionfeatures (indicative of possible overlapping or multiple bands), banddepths, albedo, and spectral slope in the analysis. These are gener-ally less useful than the mere presence of absorption bands because

Fig. 13. RELAB reflectance spectra of Tagish Lake ungrouped carbonaceous chon-drite. (a) Two different lithologies and a pressed powder. (b) Continuum-removedspectra from (a). Linear vertical offsets applied to some of the continuum-removedspectra for clarity are indicated.

E.A. Cloutis et al. / Icarus 221 (2012) 984–1001 997

they are not as diagnostic and can be affected by a wider range ofconditions. Precise absorption band positions, as discussed below,are also less reliable than the presence or absence of absorption fea-tures and approximate band positions because such absorptionbands are often shallow and noisy, precluding precise positionaldeterminations. Also, many of the spectrally active phases in CCseither show only small shifts in band position with composition(e.g., olivine) or appear to be insensitive to compositional variations(e.g., serpentine, spinel).

It should be noted that there is no reason that ungrouped mete-orites should belong to an established group, and some may be thesole representative of an otherwise unsampled parent body. Ourresults suggest that the ungrouped or uncharacterized meteoritesincluded in this study can usually be determined to be either un-ique or to be placed with a reasonable degree of confidence intoan established CC group. This ability relies on a number of factors.For example, the 0.7 lm region is where absorption bands due toFe3+–Fe2+ intervalence charge transfers in serpentine appear, whileserpentine Fe2+ crystal field transition bands appear near 0.9, and1.1 lm. Olivine can give rise to Fe2+ crystal field transitions bandsnear 0.9 and 1.25 lm (Fe2+ in the M1 site) and near 1.05 lm (Fe2+

in the M2 site) (Burns, 1970), and the 1.05 and 1.25 lm bands areusually easier to detect than the 0.9 lm band. The 1 lm region isalso where magnetite exhibits a broad absorption band, althoughit is normally difficult to discern this feature. Crystal field transi-tions in Fe2+ located in the pyroxene M2 site give rise to a bandnear 0.9 lm, and a weaker band near 1.9 lm. However, in most

CCs, olivine:pyroxene ratios are generally high enough that olivinedominates the spectrum in this region.

The olivine absorption feature does shift to higher wave-lengths with increasing Fe2+ content (King and Ridley, 1987),although the magnitude of this shift, from �1.045 to 1.085 lm,is small. The presence of accessory phases and weakness of theabsorption band normally adds a degree of uncertainty to bandposition determinations. Band position determination can be fur-ther complicated by the other phases that may be present inmany CCs and which also have absorption features in this region(pyroxene, Fe2+-bearing serpentine, magnetite, Feoxyhydroxides).

Fe2+-bearing serpentine has two absorption bands in the 1 lmregion that are broad, overlapping, and generally weak. They alsodo not appear to move with changes in Fe2+ content. CC serpen-tines normally appear to include Fe3+–Fe2+-bearing varieties(Cloutis et al., 2012b), and as a result, the presence of serpentinecan usually be discerned from absorption bands in the 0.7, 0.9,and 1.1 lm regions. In rare instances, the presence of serpentinecan be verified by an absorption band, invariably weak, at2.32 lm. Carbonates, which are abundant in Tagish Lake (Tables3 and 4) could also give rise to an absorption feature in the2.3 lm region, which is also normally weak.

The 2 lm region is where absorption bands due to crystal fieldtransitions in Fe2+ located in the M2 site of pyroxene can also ap-pear. In contrast to the 1 lm region, the 2 lm region is not inter-fered by olivine or serpentine, and reflectance is often higher inthis region, making it more suitable for determining the presenceof pyroxene (e.g., Coolidge, DaG 430, MET 01149, QUE 99038).The position of this band can be used to constrain pyroxene chem-istry (Cloutis and Gaffey, 1991). The 2 lm region is also whereFe2+-bearing spinels exhibit an absorption band (Cloutis et al.,2004). Tetrahedrally coordinated spinel Fe2+ is an intense absorber,so small amounts of such a spinel can give rise to a detectableabsorption band. Such a feature is common in CO and CV spectra(Cloutis et al., 2012c,d). Determining the presence of pyroxeneand/or spinel can be complicated by a number of factors. The pres-ence of a water band near 1.9 lm can mask a weak pyroxene band,and the spinel absorption band is broad and can overlap the pyrox-ene band. However, in general, an absorption band centered short-ward of 2 lm is characteristic of low-Ca pyroxene, while a bandlongward of 2 lm is more characteristic of Fe2+-bearing spinel.The presence of spinel can best be determined by a 2 lm regionabsorption feature with a suppressed long wavelength reflectanceincrease.

The presence of fine-grained opaque phases causes a reductionin albedo and mafic silicate absorption bands. As evidenced fromthe Coolidge and Tagish Lake spectra, opaques can induce overallslopes that range from blue to red. Metal and sulfides will intro-duce an overall red slope (Britt and Pieters, 1988; Britt et al.,1992). Thus, a red slope does not necessarily imply organics or me-tal, but a blue slope strongly implies organics; there is also someevidence that fine-grained magnetite may be able to produce amodest blue slope (Cloutis et al., 2011b). Slope changes and reduc-tions in albedo are also possible by changes in grain size. Johnsonand Fanale (1973) demonstrated that with increasing grain size(and removal of the finest fraction), CC spectra become bluer anddarker. This further complicates assigning a unique mechanismto the slopes of CC spectra. Albedo has been shown to be a usefulcriterion for assessing some of the CCs in this study, which mayhave albedos that are higher or lower than the range seen in CCgroups for comparably sized fractions. The analysis of Coolidge(and CR chondrites: Cloutis et al., 2012a) also suggests that Fe oxy-hydroxides produced during terrestrial weathering can signifi-cantly alter CC spectra, particularly those containing low Fecontent mafic silicates.

998 E.A. Cloutis et al. / Icarus 221 (2012) 984–1001

One factor that has emerged from this study is that even abun-dant fine-grained, dispersed opaques present at the levels seen inCCs are unable to fully suppress mafic silicate absorption bands.Tagish Lake is a prime example of this – mafic silicate bands persistin its spectra, albeit with depths on the order of 1%. Highly sup-pressed mafic silicate absorption bands are also seen in CCs withFe-poor silicates (e.g., Cloutis et al., 2012a).

5.1. Characterizing ungrouped and poorly-characterized CCs

Assigning or characterizing ungrouped or poorly-characterizedmeteorites should rely on multiple factors. We have found that allof the CCs and R chondrites included in this study exhibit absorp-tion features that can be related to various mineral phases thatthey contain (e.g., olivine, Fe2+ and Fe2+, Fe3+-bearing serpentine,pyroxene, spinel, Fe3+ oxyhydroxides). By determining whichphases are present, combined with band depth and albedo infor-mation, reasonable inferences can be made concerning their affin-ities to specific CC groups. We have found that absorption bandpositions, which are useful for characterizing the composition ofsingle minerals in the laboratory, are not as useful for determin-ing mineral compositions of CCs. The shapes of absorption fea-tures do have some usefulness, particularly for assessing thepresence of multiple phases in a spectrum, but again, it appearsthat only broad constraints can be placed on end memberabundances.

While some CC groups are discriminated more on textural thancompositional criteria (e.g., CO versus CV chondrites), powderedCCs will not preserve any useful textural information. We expectasteroid surfaces to be similarly devoid of textural information,and as a result, we focused our analysis of CCs on compositionalcriteria. As mentioned above, we also base our analysis on petro-logic properties that are most robustly preserved in CC spectra.Even with these limitations, we have found that the spectra ofthe ‘‘orphan’’ CCs included in this study can be characterized to asufficient level of detail to make reasonable inferences concerningtheir uniqueness or inclusion in established groups.

6. Summary

Our analysis of the reflectance spectra of a number of CCs and Rchondrites has provided useful insights into the degree to whichspectral analysis can be used for characterization, the spectral fea-tures that can be used for such characterization, and their limita-tions. As mentioned above, mafic silicate absorption features areubiquitous in the CCs and R chondrites we have examined. Com-bining information on these features along with albedo and spec-tral slopes allows reasonable inferences to be made concerningtheir uniqueness. To recap the major results of this work:

� Reflectance spectra of Coolidge show contributions from oliv-ine, and Fe oxyhydroxides produced during terrestrial weather-ing, and its high reflectance and mafic silicate band depths areconsistent with a petrologic grade >3 and inconsistent withCV chondrites.� The nature of the Cumberland Falls inclusions from spectral

analysis is inconclusive, but they do exhibit spectral featuresconsistent with their overall mineralogy.� The spectrum of DaG 430, which shares characteristics of both

CV and CK chondrites, is not fully consistent with either group.� The spectrum of EET 96029 is consistent with some CM2

chondrites.� GRO 95566, a meteorite with some affinities to CM2s, most

resembles the Renazzo CR2 chondrite, consistent with theirsimilar mineralogies. The CR group is very diverse and its limits

are not well defined (Weisberg et al., 1993, 1995). The spectralproperties of GRO 95566 can be related to its major mineralogiccharacteristics.� The spectra of Kaidun are most consistent with CR chondrites.

CR material forms the bulk of this complex polymict breccia,suggesting that the samples of Kaidun that were spectrallycharacterized did not include substantial amounts of non-CRlithologies. Spectra of larger grain sizes are more useful forassessing the nature of mineral components in this meteorite.� The reflectance spectrum of MCY 92005 is consistent with its

recent classification as a CM2 chondrite.� The R3 chondrite MET 01149 has a spectrum consistent with its

low abundance of opaques and Fe-rich silicates.� The combination of high reflectance, deep 1 lm band and, to a

lesser extent, slightly red slope and weak 2 lm region absorp-tion band, distinguishes PRE 95404 from CV3s, to which itwas initially assigned.� LAP 04840 has a spectrum dominated by olivine, consistent

with an R chondrite of petrologic grade >3. Its reflectance issomewhat lower than for the R3 chondrites, and falls withinthe range of many CCs. Its most characteristic feature is themetal–OH absorption feature in the 2.3 lm region.� Analysis and assignment of PCA 91467 (CH3) is complicated by

the presence of weathering products (Fe oxyhydroxides) whichstrongly affect its weak mafic silicate absorption bands; this isan issue also encountered in our analysis of CR chondrites(Cloutis et al., 2012a). The red slope of this meteorite is consis-tent with its high metal content, but may also be affected by Feoxyhydroxides. Its overall reflectance falls within the range formost CCs. Additional work on CH chondrites is required to bet-ter understand the spectral properties of this group.� Reflectance spectra of the howardite PRA 04401, which contains�40% CM2-like inclusions, is dominated by the howardite’spyroxene absorption bands. Expected CM2 type absorptionbands, near 0.7, and 1.1 lm are not seen and this may be dueto their absence or dominance by the pyroxene. The CC xeno-liths do lower overall reflectance and pyroxene absorption banddepths significantly, and probably add an overall red slope ascompared to inclusion-free howardites.� QUE 99038, which has been linked to CM2, CO, or CR chondrites

is not consistent with any of these groups. The 2 lm band, highoverall reflectance, and dominant olivine absorption band areall generally inconsistent with CM2 and CR2–3 chondrites. Itresembles the CO3 chondrite ALH 77003 in the 1 lm region,but differs in the 2 lm region.� The red-sloped, nearly featureless spectrum of Tagish Lake is

unique among carbonaceous chondrites. It probably arises fromthe highly aromatic nature of the organic component and itsintimate association with the phyllosilicate-rich matrix. Thematrix, which makes up the bulk of this meteorite, probablyaccounts for its spectral characteristics.

7. Conclusions

The spectral properties of the major CC groups are well enoughknown and relatable to their mineralogies that ungrouped or newmeteorites can be compared to them with some level of confidencefor determining group membership or uniqueness. As more mem-bers of CC groups are spectrally characterized, the limits of theirspectral variability will become better defined. However, ourknowledge of the causes of spectral similarities and differenceswithin and between groups and individual meteorites is hamperedby a number of factors. These include incomplete knowledge of theways in which the composition and physical disposition of opaqueminerals affect CC reflectance spectra. In addition, how much ter-restrial weathering has affected CC spectra is not well constrained

E.A. Cloutis et al. / Icarus 221 (2012) 984–1001 999

in many cases. Some of these issues can be overcome by the appli-cation of optical models and more laboratory studies of the spec-tral properties of mixtures involving fine-grained opaques.Finally, as new CCs are identified, and membership in existinggroups expands (perhaps with different petrologic grades), thespectral and compositional boundaries between groups will blur,making characterization of new meteorites more difficult.

In terms of identifying CC parent bodies, our understanding ofhow space weathering and exposure of asteroid surfaces to thevacuum of space affects them needs to be further developed. Com-bining thermal infrared with reflectance spectra can also aid in bet-ter constraining asteroid surface compositions. Finally, ourknowledge of the physical properties of asteroid surfaces mustbe improved. The common approach of using comminuted CCs tocompare with asteroid surfaces may not be valid in all cases, andneeds to be verified.

Acknowledgments

We wish to thank the invaluable and generous assistance pro-vided by many individuals which made this study possible. In par-ticular we thank the US and Japanese Antarctic meteorite programsfor recovering many of the samples included in this study. We alsowish to thank Dr. Andreas Nathues from the Max Planck Institutefor providing samples of PRA 04401 and a number of other howar-dites, Mike Zolensky and Andrei Ivanov for the sample of Kaidun,and Katsuhito Ohtsuka for DaG 430. The RELAB facility at BrownUniversity is a multi-user facility operated with support fromNASA Planetary Geology and Geophysics Grant NNG06GJ31G,whose support is gratefully acknowledged. This study was sup-ported by an NSERC Discovery grant to EAC. We also wish to thankJosep Trigo-Rodriguez and an anonymous reviewer for their valu-able and thoughtful comments and suggestions.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.icarus.2012.10.008.

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