GEOLOGICA BALCANICA. 28. 1-2, Sofia, August. 1998, p. 29-34

Geological and mineralogical features of the perlite from Kimolos island, Greece

_ -. Koukouzas

-: Piidiou Street, Maroussi-Athens, GR-151 26 GREECE

· red: 18. JJ. 1997, accepted for publication: 12. 02. 1998; reYised text rece/Yed: 02. 05. 1998)

Kp;yJac - reo/IOZU'leCKUe u MWiepaiiOZU'li!CKUe oco6eH-nepAUm06 ocmposa KUMOAOC, Tpeijwr. B HaCTOlllQCA

~ paccM&TJ'HBaJOTCll reonorHJI a MHHepanorHJI nepJIHT8 ~ KlfMonoc. nepnHT OOp830BBnCJI B nepHO.Ile MCliC.Il)' 2.0

1UB. neT H838JJ., ao apeMll nocne.11Hero ayJIIaHH'ICCJtoro 3IDIOC.:!ll B)'.IWllla KHMOJJOC a 3reAcJCoM Mope. OH Je.neHoro uae­

I!WCC'T .II)'ItOBH'fH)10 CTpyJCTypy 00.11 MHitpOCitODOM. 0Tcyr-6o.:n.w:Hx oepJIHTOBbiJI. clJpan.teHTOB B nOJJe xaparrepHJYCT ~--.... .,...,.,.. I<HMOJJOCICOfO MeCTopoll:,.lleHHJI B OTnH'fHH OT DepnH·

!IPffil Jl'TOro OCJllOBa Menoc. nepnHT COCTOHT rnasHWM o6-KJ CTei:Jla (6om.we 85% ), a OCHOBflhiC MHHepam.Hble 4laJw

...,.,.,_.,..11.83 (OJJHfOXJI83·1lHJlC3HHOB0fO COCT8B8), ICB8pU, 6H­VITaB-co.lleplKatuHH MarHCTHT H DHpoltCCH (OpTODHpOJC­

~II:.IrO COCTaBa). BynJtaHH'IecJtoe CTexno BJCJUO'f&CT .llBB BH.Il& - !;JOIJCTO'Uiax a csli38Huu a aa.11,e oH. nepnHT OCTJ'Osa

U.:JIIX - PHOJJHTOBOfO COCTBBa. B cp8BHCHHH c .llPYfHMH .JII:;Ia.:~[J!J 113 OCHOBHbiX rpe'leCJCHX MeCTopOlK.llCHHA, OH 6ora-~HTHT8HOM.

Abstract. The geology and mineralogy of the perlite from K.i­molos island is examined in this paper. The perlite produced between 2.0 and 0.9 Ma ago during the last volcanic episode of Kumolos volcano in the Aegean sea. It is green in color and presents onion-skin structure under the microscope. The absence of large perlite fragments in the field is characteristic ofK.imolos deposit compared with the perlite from the nearby island of Milos. The perlite mainly consists of glass (>85%), while the main mineral phases are plagioclase (with oligoclase­andesine composition), quartz, biotite, titaniferous magnetite, and pyroxene (of orthopyroxene composition). The volcanic glass includes two modes of water: the lattice and the OH­bound molecular water. The perlite from K.imolos island is of rhyolitic composition. lt is rich in iron and titanium compared with the other perlites from the main Greek deposits.

:L:aoo:zas, N. 1998. Geological and mineralogical features of the perlite from Kimolos island, Greece. - G!«ogica Bale., 28, 1-2; 29-34

: perlite, volcanic glass, Kimolos, Aegean.

· e, which is a volcanic glass of rhyolitic ::::ll::J?ilSIIIOn containing 2 to 5 per cent of combined

. occurs in Greece as well as in other Balkan Greece is the largest European producer

aporter of perlite. The deposits that are under ~~c- :ati·on nowadays are those of Provatas and ...._........._..~ regions of Milos island and of Kefalos ;-=:ri::&lta of Kos island, in the Aegean sea. Perlite

present on the islands of Kimolos, Lesvos, •...:~:::';:zn:liS isyros and Y ali as well as in the nor­~ of the Greek mainland. aim of the present paper is to describe the

_ ....._ dq>osit of IGmolos island, from the viewpo­geological. mineralogical and geochemical

features. The perlite of .Kimolos is of significant importance for the Greek mineral industry, as the deposit is located in the vicinity of the .Kimolos port and the island is nearby the Milos island. From the scientific point of view, this perlite differs from the other main perlite deposits of the Greek islands of Milos and Kos, as it concerns their geological and geochemical features.

Geological setting

Kimolos island is situated in the Aegean active volcanic arc, which formed during the Pliocene as a consequence of the northward subduction of the African plate beneath the Aegean one. The pre­volcanism background of .Kimolos consists of schists,

29

1 km

Fig. I. Location map of Kimolos Island

Neogene sediments and granitic intrusion while dacitic and andesitic lavas, pyrochastic and hyalo­clastite products comprise the first volcanism in the island (Fytikas et al., 1986).

The recent volcanic activity took place in Kimo­los island between the Upper Pliocene and Lower Pleistocene (3.5-0.9 Ma). Two cycles of volcanic activity are distinguished (Fytikas and Vougiouka­lakis, 1992). The first cycle comprises the lower lavas and the andesitic-dacitic lavas of Kimolos (3.5-2.0 Ma). The second cycle of volcanism dated between · 2.0 and 0.9 Ma ago and produced rhyolitic lavas. The perlite produced during the second cycle of the volcanic activity of the island.

The perlite is presented in beds and is outcropped in the northern part ofKimolos village, in the Psathi area (Fig. 1 ,2). It has green color while in some parts of Psathi area appears altered, showing a white to light green color (Plate 1, 2). The perlite ofK.imolos has extremely dense structure showing remarkable crushing resistance. The characteristic "onion-skin" perlite texture is shown even by naked eye in some places, while spherulites are very often appeared on the'surface on the perlite rocks.

Analytical techniques

The analyses of perlite were carried out at the De­partment of Geology and the Department of Che­mistry, University ofLeicester (United Kingdom). The Scanning Electron Microscope, used was a Hitachi model S-520, with an attached 'Link' Energy Dis­persive X-ray Detector, the X-ray Diffractometer was a Philips (PW 1716), with a generator Philips PW 1729, and a goniometer Philips PW 1050/25, two infra-red spectrophotometers, a research infra-red Perkin-Elmer 580B and an automatic infra-red Perkin-Elmer 1600 series FfiR, were used for the Intra-red (1. R.) analysis of the perlite. The micro­probe analyses were performed by a JEOL JXA-8600 Electron Microprobe. The chemical analyses were carried out by ab "A.R.L." X -ray fluorescence spectrometer, model8420 plus and a Philips model PW 1400, operated at 50 k V and 50 rnA.

Mineralogy

The perlite comprises the majority of glassy gro­undmass (>85%). The groundmass is characterised by a system of concentric, spheroidal cracks called

r:::::J 1 l!:!J 2 (!:E:!J 3

~ 4 5

L:;j 6 l!IZ!J 7

1 km

Fig. 2. Simplified geological sketch map ofK.imolos Island (after Fytikas, Vougioukalakis, 1992. 1 -Alluvial and recent marine deposits; 2 - perlite; 3 - pyroclastics of Psathi; 4 - pyroclastic breccia; 5 - Geronikola lava flows; 6 - andesitic and dacitic lavas; 7 - ignimbrite

30

Table I

Representative analyses of glass from Kimolos perlite

K1 K2 I K3 I K4 I K5 I K6

Si02 76.42 75.65 76.34 76.21 75.92 76.27 Ti02 0.10 0.11 0.12 0.12 0.09 0.08 Alp) 12.01 11.96 12.02 12.12 11.96 12.06 FeO 0.56 0.87 0.43 0.69 0.71 0.47 MnO 0.05 O.o9 0.02 0.04 0.02 0.08 MgO 0.07 0.12 0.03 0.06 0.09 0.04 CaO 0.67 0.68 0.63 0.68 0.65 0.61 ~ap 3.63 3.33 3.72 3.37 3.36 3.70 K.,O 3.89 3.82 3.99 3.85 3.85 3.92 sio O.o3 0.06 0.06 0.06 0.06 0.06 BaO 0.14 0.05 0.11 0.01 0.08 0.15 Total 97.64 96.74 97.47 97.21 96.79 97.44

T abl e 2

Suuistical analysis of volcanic glass composition _'Tom Kimolos perlite

I mean s. d. min. max.

SaO. 75.95 0.79 74.27 79.35 'AJ·. 0.11 0.03 0.03 0.18 6 , 12.04 0.13 11.03 12.51 ~ 0.69 0.17 0.28 1.36 lCO 0.06 0.02 0.00 0.16 M!,O 0.08 0.04 0.00 0.87 uo 0.65 0.11 0.46 1.08 - 0 3.59 0.77 2.40 6.38 -~6 3.66 1.01 0.37 4.73

O.Q3 0.03 0.00 0.06 0.09 0.08 0.00 0.23 0.01 0.01 0.00 0.04 0.01 0.01 0.00 0.04

$.d. =standard deviation, min=minimum, man=maximum

- ·c structure (Plate 3). Vesicles are often pre-in the groundmass of perlite as a result of the

'1-eeculation process which has undergone the lavas. The glass composition of perlite is exa­by Electron Microprobe and representative

. ses are quoted in Table 1. Statistics of the glass • :ses are shown in Table 2.

mineral plases of perlite of Kimolos island c:o:::Sg of quartz, feldspars, biotite, pyroxene and cpliqlae minerals. The quartz phenocrysts are ro-

in shape and occur either in the form of

NW

4

2 3 5 6

7

Fig. 3. Stratigraphic column of Psathi area, Kimolos island

inclusions in feldspars or individual small crystals. The majority of feldspars are plagioclases, which are well crystallised but small in size (0.2-1 mm). Kimolos plagioclases range from 16 to 47% An, although most of them have 20 to 30% An. Biotite is difficulty distinguishable, even under the micro­scope, due to its very small size (0.1-0.2 mm). The magnetite is titaniferous and the pyroxene is of or­thopyroxene composition (enstatite). The size of the opaque minerals, magnetite and ilmenite varies between 0.1 and 0.3 mm).

The glass is indicated, in the X -ray diffraction analysis, by a broad halo between 18 and 35 two theta angles (Fig. 5). Quartz, feldspars, and cristo­halite intensities were clearly identified, by XRD techniques. Variation of the mineral phase intensi­ties is detected in perlite from .Kimolos island with the strongest peaks usually demonstarted from the feldspars, the moderate peaks from quartz and cristobalite, and the weakest peaks from the biotite.

Two main water peaks were identified in .Kimolos perlite (Fig. 6). First an approximately symmetrical band at 1630 em·• which corresponds to the lattice or co-ordinated water and secondly a broad as­symetric band at about 3570 em·• wich corresponds to the OH -bound molecular water (Nakamoto, 1978).

Chemical composition

The perlite of Kimolos island is of rhyolitic com­position, as is determined by the X-Ray F1uorescence analysis. Representative analyses of the perlite are shown in Table 3.

SE

Ftg. 4. Geological section of Psathi area, Kimolos island

31

Table 3

Representative analyses of perlite from Kimolos island

Major elements(%)

Si02

75.40 73.93 Ti02 0.15 0.15 Alp

3 12.67 12.60

Fep3

1.19 1.30 MnO 0.06 0.06 MgO 0.09 0.20 CaO 0.96 1.00 Nap 3.69 3.33 K.p 3.71 3.61 Pp

5 0.03 0.03

LOI 2.54 3.35 Total 100.49 99.56

Trace elements (ppm)

73.48 0.15 13.56 0.95 0.05 0.08 0.93 3.54 3.40 0.03 3.68 99.84

v 5 11 7 Cr 8 BDL 161 Co 2 I BDL Cu BDL BDL BDL Ba 626 600 568 La 30 29 33 Ce 42 46 49 Nd 10 12 12 Nb 15 15 15 Zr 116 118 125 y 18 20 20 Sr 89 87 88 Rb 124 II 5 115 Th 19 16 22 Ga 14 12 14 Zn 24 26 24 Ni BDL BDL I

Rare earth elements (ppm)

74.47 72.96 0.14 0.17 12.74 14.06 1.25 1.09 0.04 0.04 0.18 0.09 1.00 0.96 3.56 3.25 3.63 3.33 0.05 0.02 3.23 3.83 100.29 99.81

ll 10 302 48 2 2 I 2 581 550 27 32 46 37 17 16 15 18 115 132 18 19 86 93 120 112 14 19 BDL 16 24 20 BDL 75

Pr Sm Eu Gd Dy Ho Er Yb Lu

4.80 2.33 0.38 1.97 2.31 0.44 1.37 1.72 0.30

3.95 2.31 0.39 1.98 2.38 0.44 1.45 1.81 0.31

4.82 4.69 4.63 2.61 2.29 2.33 0.42 0.39 0.38 2.04 1.91 1.86 2.39 2.32 2.15 0.44 0.43 0.39 1.41 1.40 1.28 1.74 1.74 1.59 0.30 0.30 0.27

Discussion

72.99 0.14 12.97 1.23 0.10 0.14 0.98 3.79 3.64 0.03 6.54 99.55

73.60 0.14 12.90 1.23 0.07 0.17 1.00 3.92 3.73 0.03 2.96 99.75

6 5 BDL 1 3 2 BDL 2 592 616 28 30 45 44 13 15 13 13 112 110 18 16 83 78 123 119 17 18 11 13 20 26 BDL BDL

4.54 3.89 2.29 2.32 0.37 0.38 1.91 2.00 2.29 2.35 0.42 0.43 1.38 1.43 1.74 1.76 0.30 0.30

The perlite from Kimolos island demonstrates cer­tain characteristic features that differentiate this de­posit from the other large perlite deposits of Greece. The green color of this perlite is characteristic ofKi-

Explanation to the plates

PLAT E I I . View of the perlite quarry in Kimolos island. 2. Outcrop of perlite from Kimolos island.

P L AT E II

a F

10 20 30 40 50 60

2 9 degrees

Fig. 5. XR. D. trace (Q=Quartz, F=Feldspar, C=Cristobalite) of-Kimolos perlite

molos deposit, compared with the perlites from Milos and Kos islandds, which are of white to gray color. In addition, the perlite of Kimolos is dense showing remarkable resistance to the crushing. The characteristic "onion-skin" perlite texture is shown even by naked eye in some places, in contradiction to the Milos and Kos per lites where is almost absent. No perlitic dome was appeared in Kimolos deposit, as it is described in Milos perlite deposits (Kouko­uzas and Dunham 1994). The absence of large per­lite fragments in the field, perlitic lahar, which ap­pears in the perlite deposits of the other Greek islands (Koukouzas, 1995), indicates the non violent eruption of the volcano producing the perlite lavas in this island.

Although the onion-skin perlitic cracks have not been identified in the perlites from the other depo­sits, these characteristic perlitic textures are well known, as characteristic feature of some volcanic rocks (Mackenzie et al., 1991, Shelley, 1993, Kadey, 1963, Whitson, 1982). The perlite from Kimolos is­land develops very well these perlitic cracks, and shows clearly the vesiculation process affecting the volcanic glass.

The composition of glass is similar to the glass of other perlite deposits (Koukouzas, 1997). The del­dspar composition is similar as well (Koukouzas, 1994). The main difference of Kimolos perlite com­pared to the other is the small size of the pheno­crysts present in this perlite. In addition, pyroxene and titaniferous magnetite is found in abundance in Kimolos perlite (Koukouzas, 1994).

The results on the modes of water in Kimolos perlite is confirmed by other worldwide perlite de-

3. Kimolos perlite structure. The perlitic cracks are dominant in the glassy groundmass. The small-sized phenocrysts are feldspars. 4. Raw perlite (a) and ex.panded perlite (b) from Kimolos island structure under the Scanning Electron Microscope (S.E.M.).

32

PLATE I

PLATE II

4000 3500 3000 2500 2000

Fig. 6. Infra-red analysis of Kimolos perlite

;osil reports (Keller and Pickett, 1954, Lehmann Knauf, 1973, Lehmann and Rossler, 1974, Na­

Ci: 1974, Wu, 1980, Acocella et al., 1984). The chemical analysis ofKimolos perlite indica­

e low content in CaO and ~0. and the high nion of FeO of the examined perlite compa­.th the other Greek deposits (Koukouzas and

1998).

elusions

~lite was produced in Kimolos island during ~d cycle of the volcanic activity in the Ae­

sea (2.0-0.9 m. y. ago). It is present only on a ""' pan of the island. No large perlitic fragments

observed in the field, which indicates the ab­of "iolent eruption of the volcano producing

products. onion-skin structure of the glass groundmass

- -- =..:=.:can be demonstrated under the microscope, · mineral phases consist of quartz, feldspars

tt:~KJclase -andesine composition, titaniferous S.l!l!ll~e.. biotite and orthopyroxene. The mineral ~55 comprises small proportion (less than 15%)

SiiDJikls perlite and have small size. The onion­,....,n:rn·..- structure is very well developed on Kimo­

'ICIII2n:·te glass while is almost entirely absent in ~~...:-of other per lites from the Greek the glass of

,_...,·rr-. from the Greek islands (Koukouzas, T 'itO main water peaks were identified in

Kiilll:lb .-u can.ic glass; the lattice or co-ordinated the OH -bound molecular water.

IE:t~JIS glass has high proportion of FeO and with the other per lites of Milos and

i~t;E:l(jks and shows a differentiated parent mag­,..___ouzas., 1 997).

1500 1000 Wave number (cm-1)

Acknowledgements. The author is indebted to Prof. A. C. Dunham for the supervision of his Ph. D . thesis, that produced this paper. He would also like to express his thank to Mr. R. Wilson, and Mr. R. Branson, University of Leicester, for their help with the Microprobe and the S. E. M. analyses, respectively. He is thankful to the State Scholarship Foundation (S. S. F.) of Greece who funded the Ph. D. thesis.

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33

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34

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