THE DEGREE OF SATURATIONOF MAGNESIUM AND CALCIUM CARBONATE MINERALS

IN NATURAL WATERS (*)

P. B. HOSTETLERU.S. Geological Survey, Mcnlo Park, Calif.

ABSTRACT

Thermodynamic data bearing on the extent of complexing between the commonionic constituents of natural waters were used to calculate the distribution of Mg+~,Ca-^+,and CO3— in certain published analyses of natural waters and hence to evaluatethe degree of saturation of these waters with respect to pure Mg and Ca carbonateminerals. Waters considered include ground waters (and a few surface waters) fromlimestones, dolomites, ultramafic rocks, and alkaline soda lakes and springs. Thefollowing table summarizes the degree of saturation of these four water types(l.Ox is thermodynamic saturation) :

Water typeSaturation ranges

Calcitc Dolomite Magnesite • Hydro-6 : magnesite

Limestone ground watersDolomite ground watersGround and surface waters

from ultramafic rocksSoda alkaline lakes

0.9A-0.5A:O.lx

5x

- 8 A :

- 5 x- 2 A -

- l O . v

0.4A-0.6A-0.5A-

15A-

- 2 A :- 7 A -- 1 4 A -

- 8 0 A -

0.03A-0.1A-0.3A-

8A-

- 2 A -- 2 A -- 4 0 A -

- 1 3 0 A -

—

0.03A- - 9A:

3 A - - 4 5 A -

Ground waters from limestones are usually supersaturated with respect to calcitcand undersaturated with respect to magnesite; the reverse is true of water derived fromultramafic rocks. All three types of ground waters are generally supersaturated withrespect to dolomite. Alkaline soda lakes, a favorable environment for precipitationof dolomite, calcite, and hydromagnesite, are strongly supersaturated with respectto all four carbonate minerals, and these supersaturation factors persist even inshallow, well-mixed water overlyjng primary bottom carbonates. Because the mineralsin the surficial layers of precipitated bottom carbonate sediments are in a higherfree-energy state than that of their pure, coarsely crystalline counterparts, highersolubility is to be expected; thus, it seems likely that many lake waters are in nearequilibria with these minerals. Greater free energy would result from a number offactors, including fine grain size, metastable ionic substitution, and crystal defects.

RESUME

Des donn£es thermo-dynamiques applicables, dans unc certaine mesure, auxcomposants ioniqucs habituels des eaux naturelles, ont 6te utilisdes en premier lieu pourcalculer la distribution des ions Mg++, Ca+*" ct COs"" dans quelques analyses d"eauxnaturelles deja publides, ensuite pour ^valuer le degre de saturation des ccs eaux encarbonates purs de Mgct deCa. Les eaux examinees comprenent des eaux souterraines(ainsi que quelques eaux de surface) preleve'es dans des calcaires, des dolomies, desroches ultra-basiques, des lacs sodiques alcalins, enfin dans des sources. Le tableauci-dessous montre le degre de saturation des eaux prelev6es dans ces divers environ-nements (1,0 x est la saturation thermo-dynamique).

(*) Publication authorized by the Director, U.S. Geological Survey.

34

Types d'eaux naturclles

Eaux souterraines dans lescalcaires

Eaux souterraincs dans lesdolomies

haux souterraines et dcsurface dans lcs roehesultra-basiques

Eaux des lacs sodiqucsalcalins

Dcgre de saturation

Calcitc

0.9.V - 8.v

0.5A- - 5 A

0 . 1 A - 2 A T

Dolomic Magnesite j

" I T0.4A: - 9A- . 0.03A- - 2A

yui L»-magnesitc

0.6.Y - 7A-

0 . 5 A - 14A

0 . 1 X - 2 A

0.3A- 40A- 0.03A- - 9.v

5A - 1 0A- ! 15.v - 80.Y ! 8A- - -1 30A! 3A- - 45A

Lcs eaux souterraines prelcvees dans lcs calcaires sont gen6ralement sursaturecsen calcitc ct sous-saturees en magncsite, tandis que la proposition inverse est realiseedans lcs eaux prelevees dans lcs roches ultra-basiqucs. Chacunc des trois varictcsd'eaux souterraines sc trouve sursaturee en dolomie. Lcs lacs sodiqucs alcalins, quiforment un milieu favorable a la precipitation de dolomie, de calcite et d'hydroma-gnesite, montrent unc forte sursaturation en ces quatre mineraux. Etccttesursaturationpersiste jusque dans les eaux moins profondes ct agitces qui recouvrcnt lcs carbonatesprimaires tapissant lc fond. Les mineraux appartenant aux couches supcrficicllcs dessediments carbonates du fond ayant une energic librc plus grande que des minerauxpurs plus largcment cristallisSs, doivent faire preuve d'unc solubility plus dev6c. IIest done probable que la plupart des eaux lacustres sont presque en equilibre avecces mineraux. Un certain nombrc de facteurs tels que finesse des grains, substitutionsioniqucs metastables, et defauts cristallins seraient la cause de cette augmentationd'energie libre.

1. INTRODUCTION

The rates of formation from solution of many carbonates are sufficiently rapidat surface temperatures to encourage gcochemists to attempt correlations betweenfield observations, laboratory studies, and thermochemical data. In this respect therehas been and is now a great deal of interest concerning the mode of origin and stabilityof calcium and magnesium carbonates in natural waters that are saturated or super-saturated with respect to these minerals. Thus, Holland and his coworkers (20) havediscussed the mode of origin of calcite and aragonite from certain supersaturatedcave waters; Garrels and others ( u ) have noted that representative ocean water issupersaturated by as much as 300 percent with respect to pure calcite; and Schmalzand Chavc (34) report the nearshore Bermuda marine waters to be greatly oversatu-rated with respect to calcite, somewhat less oversaturatcd with respect to aragoniteand moderately magnesian calcite, and perhaps only slightly oversaturatcd with respectto highly magnesian calcite.

The prerequisite conditions for dolomite formation at surface temperatures arenot yet clear, partly because of our inability to synthesize this mineral at low tempera-tures, except in high I'cO2 environments. Fortunately, in recent years there have beenseveral reports (1> 15> 35> 36) of natural primary dolomite together with chemicalanalyses of the associated water. Generally these dolomites (35> 3fi) are similar to the"protodolomites" synthesized by Graf and Goldsmith (17), which are characterizedby abnormally high CaCC>3 content and a lack of superstructure X-ray reflections,indicating that the ordered succession of Mg-Ca-Mg-Ca planes in the crystallinelattice is not consistently maintained.

Our knowledge of formation conditions for the magnesium carbonates — magne-site, hydromagnesitc(Mg4(CO3)3(OH)2.3H2O), and nesquehonite (MgCO3.3H2O)—is also scanty. One commonly encounters the concept in the literature (see, for instance,Baron and Favrc (5)) that nesquehonite is the stable magnesium carbonate at surface

.35

temperatures and hydromagnesite at somewhat higher temperatures (~100°C), yetthermodynamic data (13, 24) indicate that at 25"C a solution saturated with nesque-honitc is greatly supersaturated with respect to magnesite and that in the presence ofwater hydromagnesite is stable relative to magnesite only at Pco« values less than2 x 10~° atm. However, in natural environments at surface temperatures both nesque-honitc and hydromagnesite will precipitate directly from solution, whereas it has notyet been definitely established that magnesite can form in this way. In an aqueous ormoist environment hydromagnesite will alter more or less readily to magnesite; thehydromagnesite deposits around the Atlin, Cariboo, and Kamloops districts of BritishColumbia (u> 29) are good examples. Perhaps the best, but not conclusive, evidenceof primary, low-temperature magnesite has been reported by Alderman and von derBorch (2> 3) from lagoonal environments around the Coorong district of South Austra-lia. Here, in one lagoon, an aragonite-hydromagnesite assemblage was found fromthe sediment-water interface to a depth of 9 inches, whereas in another lagoon some8 miles distant, a magnesite-dolomite assemblage was reported from the interface toa depth of 10 inches. There have been a number of other descriptions (4> 9- 18> 28> 31>

33, 37, 38) of magnesite allegedly formed at surface temperatures. In general suchmagnesite is found either in evaporite facies (18' 33 ' 37), where [the reduced activityof H2O due to very high salinity may have enhanced the probability of direct magnesiteprecipitation by dehydration of the solvated Mg ions, or as a weathering alterationproduct of ultramafic masses (4> 9- 28).

In the present report analyses of waters derived from a number of rock types andenvironments were studied and the chemical activity of each pertinent ion calculatedwith a view towards: a) determining the degree of saturation of carbonates in watersderived from parent carbonate rocks and b) relating such relative saturation to that ofwaters from which the same carbonate minerals are found to have precipitated atsurface temperatures. Waters considered from the standpoint of (a) include groundwaters derived from limestones, dolomites, add ultramafic rocks. Waters derivedfrom ultramafic rocks were considered because of the nonexistence of analyses ofwaters derived from magnesites or other magnesium carbonates. Some, at least, of thereported ultramafic rocks contain appreciable amounts of magnesium carbonates.Waters considered from standpoint (b) are alkaline soda waters (mainly lakes), 'which are a favorable environment for the precipitation of calcite, dolomite, andhydromagnesite. These waters arc typically characterized by large concentrations ofsodium, significant concentrations of sulfate and chloride ions, and distinctly alkalinepH values (pH 5; 8.5).

2. RESULTS

Sixty-two water analyses were individually recalculated with the aid of availablethermochemical data (12> 13- 24) to determine the molal concentrations of the variousaqueous species that are present in each sample. Calculations revealed that for manywaters some or all of the following complex species are significant: CaCO,V\ CaHCOj,CaSCV, MgCo3°, MgHCOij, MgSO4°, NaCOg, NaHCO3°, NaSOl, and KSO^.The dissociation constants used for determining molal concentration of these complexspecies are those reported by Garrels and Thompson (12) except that of MgHCOJ;the value used was the one recently reported by the author (21). These data, includingthe pH of each water and its determined ionic strength, were used to calculate theactivities of Mg++, Ca++, and CO" r in each sample. Calculation methods, which arerather cumbersome, are not reported here as they are essentially the same as thosereported by Garrels and Thompson (12) in determining a chemical model for sea water.The ionic strength of sea water is 0.7 (12), but none of the samples used in this studyhad an ionic strength greater than 0.45.

36

TABLE IDistribution of Ca, Mg and CO3 in natural waters

Locationg(

PCO2pH

- l og ( 3 ) I! 1

I " C a H

- log(3) I— log(3) j - Iog( 4 ) 1 - l 0g ( 4 )I

Departure from saturation(5)

! ape/Kspe \ apm/Kspm

Precipitated

"~! phase 0 ) I Rcfer-,)*; (C) I ence

7.07.77.58.08.2

I

7.37.67.97,67.617.55

8.27.57.97.67.4

7.6

7.2

8.0

7.2

7.6

7.9

8.0

8.0

7.9

8.2

7.6

8.4

8.2

8.7

8.1

8.4

10.1

8.7

0.00180.0040.0050.0050.009

7.8 I 0.0120.015

1 0.0160.0040.0060.00450.0047

0.0080.0040.0090.0100.03

Ground waters from limestones and marbles \Gainesville, Florida, limestone j 2.13Brooksville, Florida, limestone i 2.49Irondalc, Alabama, limestone 1 2.30Lake City, Florida, limestone 2.73Bardstown, Kentucky, limestone ! 2.78Nit. Juliet, Tennessee, limestone | 2.18Birmingham, Alabama, limestone 1.88Roswell, New Mexico, limestone 2.27Sylacauga, Alabama, marble 2.71Baltimore County, Maryland, marble I 2.27Black chasm Is cave, Volcano, Calif, lake surface I 2.36Black chasm Is cave, Volcano, Calif. 40' below surface j 2.29

Ground waters from dolomites •West Allis, Wisconsin ! 2.86Copper Ridge, Alabama I 2.34Irene, Pretoria, Transvaal 1 2.36Bainbridge, Ohio ! 2.06Fort Recovery, Ohio I 2.04

Ground and surface waters from ultramafic rocks 1Lydenburg, Transvaal, 413, ground water ' I

pyroxenite ] 2.01 jLydenburg, Transvaal, 414, ground water

pyroxenite I 1.52 ILydenburg, Transvaal, 415, ground water, . .

peridotitc I 2.28 1Rustenburg, Transvaal, 307, ground water, I

gabbro or pyroxenite 1.83Pretoria, Transvaal, 302, ground water,

gabbro or pyroxenite 2.36Krantzberg, Transvaal, 445, ground water i

serpentine and pyroxenite 2.15Marico, Western Transvaal, 538, spring in

gabbro and pyroxenite 2.17Shasta Valley, Calif., ground water, I

serpentine, 41/5-4N1 i 2.47Shasta Valley, Calif., 4I/5-4D1, ground

water, serpentine 2.49Shasta Valley, Calif., 41/5—9F3, ground , I

water, sepentine 1 2.93 1Shasta Valleyr Calif., 42/5—33 Ml, ground

water, ser.pcntinc 1 2.17Shasta Valley, Calif., 4 2 / 6 - 10JI, ground '

water, serpentine 2.94 'Shasta Valley, Calif., 41 /5 - 9P, surface I 1

water, serpentine | 2.99 IClear Creek, San Benito County, California, I

drains serpentine — June 13, 1955 ! 3.01Clear Creek, San Benito County, California 1 I

drains serpentine — June 28, 1959 ' 2.33 '

Alkaline soda springs and lakes •Kecne Wonder Springs, Inyo County, California, 1 I

sample 1 1.39 IKeene Wonder Springs, Inyo County, California, 1

sample 2 , 2.45 !Spring Water, 141 Mile House, Caribou Road, 1 1

British Columbia | 4.33 [Spring Water near North Fork of Riskc | I

Creek, British Columbia i 2.58 1St. Andra, lake, Seewinkel, Burgenland, I 1

Austria I 2.97 I 8.63Langc-Lacke, lake, Seewinkel, Burgenland, I I

Austria | 2.90 | 8.69Darscho, lake Seewinkel Burgenland, , i

Austria, - July 8, 1957 3.02 | 9.00Darscho, lake, Seewinkel, Burgenland, Aug. 5, 1958 I 3.25 | 9.18Halbjochlacke, lake, Seewinkel, Burgenland, I

Austria —July 8, 1957 ! 3.08 I 9.45Halbjochlacke, lake, Seewinkel, Burgenland, i I

Austria —June 18, 1958 2.94 | 9.36Fuchslochlacke, lake, Seewinkel, Burgenland, I

Austria | 2.98 | 9.31lllmitzer Zicksee, lake, Seewinkel, 1 1

Burgenland, Austria —July 8, 1957 3.23 , 9.45lllmitzer Zicksee, lake, Seewinkel, I

Burgenland, Austria —June 18, 1958 I 3.00 I 9.16Neusicdlersee-Podersdorf, lake, Seewinkel, . I

Burgenland, Austr ia—June 18, 1958 ] 3.25 8.85Neusiedlersee-Podersdorf, lake, Scewinkel, i i

Burger.land, Austria— July 1, 1958 1 3.17 | 8.81Neusiedlcrsee-Podersdorf, lake, Seewinkel, 1 I

Burgenland, Austria — August 5, 1958 , 3.27 | 8.88Neusiedlersee-Podersdorf, lake, Seewinkel,

Burgenland, Austria — September 1, 1958 ! 3.30 8.94Big Soda Lake, Nevada j 3.76 I 9.6Pyramid Lake, Nevada : 3.00 i 8.9Walker Lake, Nevada I 3.30 ! 9.3Abert Lake, Oregon , 3.82 I 9.8Borax Lake, California 3.64 1 9.7Little Borax Lake, California I 3.94 : 10.0Lake Balkhash, USSR, western pool, southern part 1 2.90 I 8.3Lake Balkhash, USSR, western pool, northern part ! 2.93 j 8.4 | 0.03Lake Balkhash, USSR, middle pool, western part I 3.50 1 9.0 1 0.05Lake Balkhash, USSR, Lepsinskij pool I 3.55 9.15 0.08Lake Balkhash, USSR, Biurliuj-Tupinskij, pool, west | 3.59 I 9.2 I 0.09Lake Balkhash, USSR, Biurliuj-Tupinskij, pool, east | 3.53 9.15 0.09Lake Kingston, South Astralia j 4.67 9.2 0.45

cean waterRepresentative sea water . 3.30 8.10 0.7

II

i 0.06

J 0.06

! 0.07

1 0.04Ij 0.019

I 0.019

j 0.0330.032

I 0.15

J 0.16I 0.10I

I 0.19

I 0.09

I 0.03

I 0.03

1 0.03

0.03I 0.45I 0.08

0.12I 0.18I 0.28

0.180.180.025

0.010 I

0.012 II

0.013

0.0065

0.005 I

0.014 i

0.016 I

0.010 I

0.007 1

! 0.005 '

I 0.007 ,

J 0.008

I 0.004

I 0.016 1

0.017 1

i

3.513.052.973.153.022.742.862.753.142.963.002.99

3.283.202.973.362.75

3.50

3.60

4.00 j

3.65

3.69 I

3.72 I

4.19 j

3.88

3.73 j

4.14 I

«7 j3.82 i

4.19 I

4.68 J4.13 I

Ii

3.12 ]

3.77 !

3.50

3.98

4.374.57

5.51

5.09

5.18

5.02

4.87

3.79

3.90

3.95

3.954.724.334.645.145.155.093.383.383.734.024.104.133.03

2.58

3.22

3.34

3.52

2.46

2.76

3.07

3.293.43

4.20

4.19

4.07

3.51

3.37

2.79

2.81

2.82

2.833.112.933.234.464.134.392.872.782.712.652.602.592.18

1.77

3.653.754.023.353.053.173.063.073.523.583.923.82

3.083.372.992.73 I2.85 i

2.69 I

2.62 j

2.62 I

2.88 •

2.98 j

2.57 j

2 .52 I

2.74 !

2.89 I

2.94 I

2.82 J2.78 !

3.02

2.57 1

2.52 I

3.143.00

6.255.215.424.804.504.705.405.195.025.195.265.31

4.585.46 I4.68 I4.985.36 I

4 . 9 3 '•

5.24 ,

4.41 ,

5.55 j

5.28 !

4.47 :

4.29 I

4.59 I

4.81 j

4.65 |

5.09 J

4.26 1

4.71 II

3.73 ,

4.25 I

4.71 '

3.76 I

2.25 I3.30 1

3.83 I

3.76 I

I2.30 I

2.34

2.48

2.45

2.79

3.67

3.67

3.63I

3.542.683.32 I2.832.342.362.064.414.253.623.373.313.354.39

5.33

9.768.268.397.957.527.448.267.948.168.158.268.30

7.86 I8.66 ,7.658.34 I8.11 I

II

8.43 I

8.84 i

" • I9.20 I

8.97 ' I

8.19 '

8.48 1

8.47 I

7.83

8.79 I

8.86 i

8.08 j

8.90 '

8.41

8.38

7.53 I

7.33 ;

7.74 I

7.517.57

7.81

7.43

7.66

7.47

7.66

7.46

7.57

7.58

7.497.407.657.477.487.517.157.797.637.357.397.417.487.42

7.91

9.908.969.448.157.557.878.468.268.548.779.189.13

7.668.837.677.718.21

7.62

7.86

7.03

8.43

8.26

7.04

6.81

7.33

7.70

7.59

7.91

7.04

7.73

6.30

6.77

7.93

7.10

5.77

5.76

6.59

6.83

6.436.43

6.50

6.53

6.55

5.96

6.16

6.46

6.48

6.45

6.375.796.256.066.806.496.457.287.036.336.025.915.946.57

7.10

19.6617.2217.8316.1015.0715.3116.7216.2016.7016.9217.4417.43

I16.32

! 16.05

16.70

I 15.44

j 17.63

! 17.23

' 15.23II 15.291 15.801

I 16.24

I 16.38

I 16.77

[ 15.12

! 16.63

I 14.71

I 15.15i

1

1I 15.76j 14.63

II

I —

I 13.921 14.57

i 13.94I 14.00

I 14.31

13.96

14.21

13.43

13.82

13.92

14.05

14.03

13.8613.1913.9013.5314.2814.0013.6015.0714.6613.6813.4113.3213.4213.99

15.01

47.3543.2345.34

I 39.801 37.301 39.18I 41.841 40.651 41.34

42.6944.24

1 44.11

15.52 , 37.6617.49 I 42.8615.32 I 38.2016.05 , 38.86

40.68

' 38.35

I 39.80

! 35.71

I 41.77

40.56

35.89

I 34.95

' 36.73

I 38.19

I 37.31

I 39.35

35.10

I 37.81

32.07

34.63

40.21

35.84

28.63

30.34

33.27

34.18

32.5832.36

I 32.80

i 33.06

j 33.10

I 30.49

i 31.53

32.47

32.63

32.41

32.06 I29.2831.8830.8133.2632.2031.7436.1135.0731.7030.4129.9330.1131.49

34.87

0.041.20.892.56.67.91.22.51.51.61.21.1

3.00.484.91.01.7

0.81

0.32

0.85

0.14

0.23

1.4

0.73

0.74

0.63

0.36

0.30

1.8

0.28

0.85

0.91

3.2

6.5

10.

4.0

6.85.9

3.4

8.1

4.8

7.4

4.8

7.6

5.9

5.8

7.18.74.97.47.36.815.3.65.19.88.98.57.38.3

2.7

0.010.090.030.582.31.10.280.450.230.140.050.06

1.80.121.71.65.0

2.0

I.I

7.6

0.30

0.45

7.4

13.

3.8

1.6

2.1

1.0

7.4

1.5

41.

14.

0.95

6.5

140.

140.

30.30.

24.

23.

89.

56.

28.

27.

35.130.46.71.13.26.29.4.37.6

38.78.

100.93.22.

6.5

0.050.780.382.89.16.91.42.51.41.10.600.60

5.50.586.93.02.2

3.0

1.4

6.0

0.48

0.76

7.6

7J.

4.0

2.4

2.0

1.3

8.7

1.5

14.

8.3

4.2

15.

I 17.

34.32.

!i 22 .I' 3 3 .II 2 5 .I 60.

; 39.

I 3 5 .I 30.II 30.Ii 37.I 79,

36.55.23.32.50.

9.115.46.63.69.62.32.

10.

0.0010.020.0040.110.440.150.30.060.040.020.0080.009

0.360.020.260.180.06

0.24

0.11

1.1

0.03

0.07

1.0

1.7

0.60

0.26

0.44

0.14

1.6

0.33

8.9

2.0

0.08

1.0

65.

24.

4.5

2.6

6.67.6

5.9

5.0

4.9

22.

12.

7.1

6.5

7.4

8.945.10.18.4.58.3

11.0.871.6

11.23.30.28.13.

c

c

c, h

c, h

C d

C d

C d

c, d

c(7Jc (?)c, d

c, dC d, h(?)c, d,h(?)c.d, h(?)c,d

393939393939393939392727

3939393939

6

6

6

6

6

6

.6.

26

26

26

26

26

26

10

10

39

39

29

29

23

23

2323

23

23

23

23

23

23

23

23

234040404040401515151515151

12

(') For example, Atmospheric COo —- lO"3-40 atm., —log PCO2 •= 3.40.(2) Ionic strength.(3) Calculated activities for these ions.(4) Subscripts c, m, d, and h represent calcite, magncsite, dolomite, and hydromagnesite respectively, apc - («ca+"') («C()3~~), apm - (WMK1""1") («CO3—), apt - («ca++) (a« 8

T + ) Ocos—)2 aph — (aMg++)4, (aco3—)3

(5) 1"OH~Y" Kspc - 10~8-34, Kspm -• 10"7-91, Ksp& -- 10 17-00, Ksp\, - - IO~35-87. Value for quotient of 1.0 is thermodynamic saturation; < 1.0 is undcrsaturation, > 1.0 is supersaturation.(6) Phases precipitated from springs or lakes at surface temperatures.

Four activity products — (aca+-) (acof), (oMgT+) (nct>3~~), («ca'*) (a.Mg+-)

(oco3~~)2, and (aMg+')4("co3" ~)3(aon~)2 — were derived from the calculated ionicactivities for each sample. These values, abbreviated as apc, apm, apa, and apn, may becompared respectively to the thcrmodynamic solubility products (Ksp) of calcite,magncsitc (or nesquehonite), dolomite, and hydromagnesite to determine the extentof departure of the sample from thermodynamic saturation. For instance, at 15UC,Ksp calcite is 10~8-34 (24), and a solution is thermodynamically saturated with respectto calcite when the activity product (aca++) ("co3~") is equal to lO"8-34, whatever theinvidual activities may be for Ca^+ and CO" " ions. The important point is that ther-modynamic saturation represents the value towards which the appropriate activityproduct (ap) should tend to approach if the solution is supersaturated or is under-saturated and in contact with a carbonate mineral. If this tendency is not apparent,the amount of departure from thermodynamic saturation gives us some informationconcerning the persistence of metastability and (or) conditions for incipient precipita-tion of the carbonate mineral itself.

The quotient ap/KSp is a convenient measure of the amount of departure fromthermodynamic saturation; values for the quotient of greater than 1 represent super-saturation, and values less than 1 represent undcrsaturation. These values will befrequently referred to in this report and the reader should note that they refer to theexcess (supersaturation) or deficiency (undersaturation) of only one of the composi-tional ions of the carbonate. That this is so can be discerned from the solubility pro-duct of calcite («ca~+) (aco3" ~) =- 10" 8-34, where a change of, say, an order of magni-tude in either Ca "1" or CO^~ will be reflected by a change of an order of magnitudein the solubility product. To facilitate comparisons between carbonates, especiallycationcomparison.thequotients^prt/K^j,^)1.'2 and (apn/Kspn)114 are used here for dolo-mite and hydromagnesite respectively. Thus, a quotient of 5 for calcite indicates thateither aca++ or oco3, is 5 times that required for thermodynamic saturation, a quotientof 5 for dolomite indicates that cither ocoa" or the product (oca++) («Mg++) is 5times that required for saturation, but for hydromagnesite a quotient of 5 appliesonly to oM*'+ (KsPh - (aMg

+-)4(«co3 )3(«oir)2).

The value for Ksp magncsite is 10 7-91 (24). The ZlF° hydromagncsite value givenby Garrels and others (13), and the free-energy of formation values for Mg~*~+, COj~,and OH~ listed by Latimer (24) were used to derive a Ksp iiydromaRnesite value of10-35.87 A KSJ) neSqUehonite value of 10~5-51, which is somewhat lower than thatgiven by Latimer (2/1), is consistent with the more recent solubility data for this mineralof Kazakov and others (22). There is considerable discrepancy between reported /IFvalues for dolomite at 25°C, and none of the available thermochemical data (l3>19, 30) w a s used_ Instead, a Ksp dolomite value of 10~17-00was used. This figure wasarbitrarily chosen by Holland and his coworkers (20) as being most consistent withanalyses of cave waters derived from solution of dolomitic rocks and is very similarto a Ksp<t of 10~1(i-78 derived from Halla's (19) value for zlF dolomite-

Ksp values are, of course, temperature dependent, but the Ksp values given aboveare for 25 °C. The temperatures of most of the water samples used in this study variedfrom 17" to 25 °C. A few samples were slightly cooler, one was slightly warmer, andfor a considerable number of surface samples, collected during the summer months,no temperatures were listed in the original sources. The solubility of calcite at I7UCis about 20 percent greater than at 25°C (2r>); the other carbonates are probablysimilar. This sort of error, not significant for the purposes of this study, is roughlycomparable to an error of 0.1 pH unit between true and measured pH. Most pH valuesreported for samples used here were undoubtedly determined in the laboratory; con-sequently, many pH measurements are probably no more accurate than : j- 0.2 pH unitof the true pH of the sample at the time of collection. The pH measurements for alka-line soda lakes are apt to be the most accurate because these samples were nearly inequilibrium with atmospheric CO2 at the time of collection (no notable gain or loss

37

of COo from field to laboratory). An error of | 0.2 pH unit yields an error of about40 percent for the stated quotient ap/Ksp.

The results are shown in table 1. Note that fi represents the determined ionicstrength and that Pco2 values, individual ionic activities, and calculated activity pro-ducts (ap"s) are expressed as negative logarithms. Much of the data of table 1 is bestillustrated by separate figures.

In figure 1 pH is plotted against calculated Pco > for each sample, and the bufferingeffect of the carbonate-bicarbonate couple on the pH of natural waters is illustratedby the linear trend, or "belt", of all the analyses. Groundwatcrs from limestones,dolomites, and ultramafic rocks appear to have similar ranges of pH and Pco2 values,with the latter varying from 10" :)-no to lO"1-50 atm (3 to 100 times atmospheric CO2).The alkaline soda lakes, having Pco2 values ranging from 10~300 to 10 4-(l0, are, asmentioned above, more nearly in equilibrium with atmospheric CO2. Most of theselakes are slightly supersaturated with respect to atmospheric CO2, but a few veryalkaline ones (pH > 9.5) are slightly undersaturated. Slight supersaturation is pro-bably common because of subsurface discharge into lakes of ground waters withhigher Poo.> values such as those plotted from limestones, dolomites, and ultramaficrocks. In general this effect should be less noticeable at higher pH values because ofthe progressively greater total carbonate content of the lakes. The very low Pco>value for Lake Kingston (pH 9.2, Pcoj ~ 10 4-67) is apparently due to photosynthesiseffects (1) in a very shallow body of water.

The heavy solid lines in figure I separate ionic "domains"; in each domain oneof the lettered aqueous species, either M+- (M — Mg or Ca), MHCOf, or MCO30,accounts for most of the aqueous M, and along a line separating two domains theactivities of adjoining species are equal. Actually there should be separate but parallellines for distinguishing the domains of the calcium and magnesium aqueous species,but the dissociation constants for MgHCO^ and CaHCOg and those for MgCCVand CaCO.i0 are sufficiently similar (see Garrels and Thompson C12)) that the separa-tion is insignificant for the purposes of this study.

Thus, in groundwaters from limestones, dolomites, and ultramafic rocks most,if not essentially all, of the aqueous Ca and Mg is present as Ca++ and Mg+~. In thealkaline soda lakes, however, where total carbonate greatly exceeds aqueous Ca andMg, significant amounts of Ca and Mg (as much as 90 percent) are present mainly asMCO3'1 plus some MHCCKj. Sulfate complexing as MSO40 may also be important,so that as little as 5 percent of the total aqueous Ca and Mg is present as Ca++ andMg++. These data are given to emphasize the importance of quantitatively accountingfor such complexes in attempting to explain saturation conditions in alkaline waterswhere carbonates may precipitate.

The extent to Which the natural waters studied here are saturated with respectto calcile, dolomite, and magnesite is illustrated respectively in figures 2, 3, and 4.In every figure, the abscissa is «co3~" ; in figure 2, the ordinate is flca"+, in figure 3[(«Ca~~) (0Mg"l+)]I/2.,and in figure 4, OMg'1"". In figures 2 and 4 a solid line representsKip at 25"C. In figure 3 the range of Ksp values for dolomite, using the values ofHalla (10), Robie (30), and Garrels and others (13) is illustrated by dashed lines, andthe value of Holland and his coworkers (20), from which the apjKsv quotients werecomputed, is shown by a solid line.

Perhaps the most striking gross feature of these figures is the high slate of" super-saturation that exists in many natural waters, and especially in alkaline soda waters,with respect to calcite, dolomite, and magnesite. Table 1 indicates that a similar situa-tion exists with respect to hydromagnesite. No waters were encountered which weresaturated with respect to nesquehonitc, although several approached this value. Table2 summarizes the range of quotients for each water type.

38

Fig. 1 — Pcoo- pH range of natural water types considered. The letters c, d, and hrepresent, respectively, calcite, dolomite, and hydromagnesite. Heavy solid linesseparate ionic "domains"; in each domain the lettered species, either M'~+(M -- Mg or Ca), MHCCb*, or MCO30, accounts for most of the aqueous M. Thenature of the bottom sediments in many alkaline soda lakes is unknown, but acomparison of Na/Ca ratios in the lakes and their tributaries provides indirect evi-dence of calcite precipitation. Where this evidence is available, the analysis plotsare designated by a half-filled circle (Cl). The dot-dash line joining two analysisplots from Kecne Wonder Spring illustrates drop in fcoo and increase in pH be-tween 150 feet and 1,000 feet downstream from vent. Representative ocean water(12) is designated by a cross (-1 ).

39

TABLE 2

Range of each water type in amount of departure from saturation with respect to calcite, dolomite, magnesite, nesquehonite, and hydromagnesite

Water type

Ground waters from limestones and marblesfrom limestonesfrom marbleslimestone cave water

Ground waters from dolomites

Ground and surface waters from ultramaficsground waterssurface waters

Soda alkaline springs and lakesspring water precipitating calcitespring water precipitating hydromagnesite

, lakes

Representative ocean water

Calcite

0.9 — 81.51.1

0.5 — 5

0.1 — 20.3 — 1.0

3 — 6

5 — 10

2.7

Range (*)

Dolomite

0.4 — 91.20.6

0.6 — 7

0.5 — 91.5 — 14

4 — 1 5

15 — 80

10

Magnesite

0.03 — 20.2

0.06

0.1 — 2

0.3 — 131.5 — 40

1.0 — 6140

8 — 130

6.5

Nesquehonite

—

—

0.001 — 0.050.006 — 0.2

0.60.03 — 0.6

—

Hydromagnesite

—

—

0.03 — 20.3 — 9

403 — 45

1.8

(•) Amount of departure from saturation is expressed by the quotient ap/K.sp.

f1 = 1

. g s c• e - S ^

5 g e t

a.

" :ti

13 < x ;

-

-

_

/

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~\ 1

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/

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Fig. 2 — Departure from saturation with respect to calcite. Thermodynamic satu-ration along line Kspc = 10~8-34. The letters c,d, and h represent calcite, dolomite,and hydromagnesite. Four analysis plots from Neusiedlersee are connected by adotted line, six analysis plots from west to east of Lake Balkhash are connectedby a dashed line, and two analysis plots from Kcene Wonder Spring are joinedby a dot-dash line. Representative ocean water (12) is designated by a cross (4 ).

41

_ y

/

- //

9^y

,«y

///•>

•? //

•/

/ u

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v x

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% % %•n V* *•

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i

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a

i l l- o o

= <>o

<

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Fig. 3 — Departure from saturation with respect to dolomite. The letters c, el, and hrepresent calcite, dolomite, and hydromagnesite. Presumed thcrmodynamicsaturation along line Kspa — 10! 17-00, but three other dashed Kspa lines (work ofHalla (1!l), ROBIE (30), and Garrels and others (13)) possibly represent thermody-namic saturation more correctly. Four analysis plots from Neusiedlcrsee areconnected by a dotted line, six analysis plots from west to east of Lake Balkhashare connected by a dashed line, and two analysis plots from Keene Wonder Springsare joined by a dot-dash line. Representative ocean water (12) is designated bya cross (-••).

42

From figure 2 it is apparent that alkaline soda lakes, from many of which calcitcprecipitates, are regularly and uniformly supersaturated with respect to this mineralby a factor of 5 to 10 times. Ground waters from limestones and dolomites are muchmore variable than the alkaline soda waters with respect to calcitc saturation. Mostof these ground waters arc supersaturated, a few by factors as high as those encounteredfor alkaline soda waters. It is perhaps significant that analyses of ground waters fromtwo marbles, the calcites of which have been presumably rccrystallizcd to a coarser,more thermodynamically stable variety, indicate only slight supersaturation. Notsurprisingly, waters from ultramafic rocks are generally undcrsaturatcd with respectto calcite.

Supersaturation of 10 times apparently constitutes a definite ceiling for calcite,and this is illustrated in figure 2 by the dashed line connecting six analyses of watersfrom Lake Balkhash, U.S.S.R. The analyses, shown in Table 1, were of waters fromsix different stations, or pools, ranging from the western (no carbonate precipitation)to the eastern end (considerable carbonate precipitation) of the lake. From west toeast, there is a marked increase in pH, salinity, magnesium and carbonate content,and a decrease in calcium (15). According to Sapozhnikov (a2) the shallow characterof the lake (nowhere greater than 90 feet) does not permit a vertical zonation of thewaters.

Turning to dolomite saturation, it is apparent from figure 3 that all water typesunder discussion show a complete disregard for the various postulated thermodynamicsolubility products of this mineral. Waters from dolomites, limestones, and ultramaficrocks all indicate roughly similar ranges of supersaturation, and this supersaturationcommonly amounts to 5 to 10 times the value of Holland (20) or Halla (1!)). Thesesupersaturation values would be even higher, of course, if the values of Robie ('1())or Garrels and others (13) are more nearly correct. The supersaturation values for thealkaline soda waters are still greater, ranging from 15 to 80 times.These supersatura-tion values are surprising for waters derived from limestones and dolomites, andalthough the evidence is scanty, the suggestion is that ground waters do not equili-brate readily with dolomites.

For those alkaline soda lakes that precipitate dolomite (or prolodolomite) theapt is 1O~)4-00 or higher, but in no case higher than 10~13-nn. The solubility product(K<sP) at 25°C for protodolomite probably lies within this range of values. Althoughopa has a fairly narrow range, from 10"1'1-00 to 10 13-(l() for those alkaline soda lakesin which dolomite is forming, it is not clear whether the 1O~13-00 figure represents asupersaturation ceiling for this mineral. If there is a supersaturation ceiling for dolo-mite, the assemblage calcite plus dolomite should effectively limit the buildup ofmagnesium in alkaline carbonate waters. The formation of hydromagnesite, magnesite,or nesquehonite would also limit magnesium buildup. The occurrence of calcite-hydromagnesite assemblages in British Columbia (u> 29) and calcite-dolomite-magne-sium carbonate (hydromagnesite ?) assemblages in the sediment at the eastern endof Lake Balkhash (15) suggest that a supersaturation ceiling for dolomite is not alwayseffective in limiting an increase in aqueous magnesium. Kinetic factors in a dynamicenvironment are probably important.

The highest determined supersaturation values arc those with respect to magnesite(fig. 4). In alkaline soda waters these range from minimum values near 10 times tomore than 100 times. Most of the waters from ultramafic rocks are also supersaturated,some quite strongly, whereas almost all those from limestones are undersaturated.Four of the five waters from dolomites hover near magnesite saturation. Lack ofevidence of direct magnesite precipitation at 25°C, at least from the waters studied,indicates that Mg!"' and COg~ may build up in solution until («Mg++) (tico's )reaches a value of about 10 5'50, the KS7) for nesquehonite. In distinctly alkalinewaters (pH > 8.5), hydromagnesite will probably precipitate before nesquehonite.From table 1 the apn's, for the five waters probably precipitating hydromagnesite are

43

Fig. 4 — Departure from saturation with respect to magnesite and ncsquehonite.Thh letters c, d, h, m, and n represent calcite, dolomite, hydromagnesite, ma-gnesite, and nesquehonite. Thermodynamic saturation along lines Kspm —10~7-91

and Kspn = 10"5-51. Four analysis plots from Neusiedlersee are connected by adotted line, six analysis plots from west to east of Lake Balkhash are connectedby a dashed line, and two analysis plots from Keene Wonder Springs are joinedby a dot-dash line. Representative ocean water (12) is designated by a cross .( + )

44

1

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•a

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-

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/

/

| | . . s

! ! ; •m

16-i-01

/

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0 ©

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; /

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• • •

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y

i

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X

X

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1

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/

1

X

XX

X

XX

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/

: \

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/

/

a

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u

Ga

I

X X

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x Ll

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+

/

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c

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4,

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0 ^ '/

• P.

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o

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l

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Fig. 5 — Separation of water types by departure from saturation with respect tocalcitc and magnesitc. The letters c, d, h, m, and n represent calcite, dolomite,hydromagnesite, magnesite, and nesquehonite. Area of "residual concentration"(alkaline soda waters precipitating two or more Ca-Mg carbonates) is boundedby apo's of 10-7S4 and lO"7-34, apa's of 10-14-00 and 10"1300, and Kspn- Theap's determined by Holland and others (20) for cave waters in limestones anddolomites are represented by half-filled squares (Is) and triangles (dolo) Represen-tative ocean water (12) is designated by a cross (+).

45

all around 10 30-00 or slightly higher. This figure corresponds to a supersaturation of30 times with respect to hydromagnesite, and such a high degree of supersaturationmay be necessary to induce precipitation. Only one other water, that from Big SodaLake, Nevada, is as highly supersaturated, but the nature of precipitated carbonates,if any, from this lake is not known.

On figure 5, a summary plot of apc against apm, the four water types are clearlyseparated on the basis of their relative degree of saturation with respect to both calciteand magnesite. Most of theplotsof alkaline soda waters, including all thosethatarepre-cipitating calcite plus dolomite and (or) hydromagnesite, fall in an area of "residualconcentration", which is shown on figure 5 by heavy solid lines. This area is boundedby ape values of 10~7M and 10"7-3'1 (5and 10 times calcite supersaturation), «/?<* valuesof 10"14-00 and lO""-011, and the solubility product of nesquehonite (10 "5-s l). Asmentioned previously, the pH's of most alkaline soda waters are sufficiently high toinduce precipitation of hydromagnesite before an apa value of 10 l3-()n, or the solu-bility product of nesquehonite, is reached. This area illustrates the probable limitsof supersaluration with respect to calcite and dolomite that can be attained in alkalinesoda waters and very possibly other waters, such as sea water of comparable ionicstrength.

Activity products for calcite and dolomite as determined by Holland and others(20) for cave waters of Virginia and Pennsylvania are also plotted on figure 5. Themoderate to high supersaturation of these cave waters with respect to calcite anddolomite is in good general agreement with those reported here from ground watersfrom limestones and dolomites. Holland and his coworkers (20), however, point outthat those cave waters which have ample opportunity to equilibrate with cave air,and consequently have ceased precipitating calcite, are much less apt to show signifi-cant supersaturation with respect to this mineral. Waters from the Black Chasmlimestone caves (see table 1) also fall in this category.

3. CONCLUSIONS

The supersaturation values encountered in various water types have been largelyconsidered without reference to rate of thermodynamic equilibration or persistenceof metastable supersaturation, but it seems that for magnesite at least, high supersa-taration values, probably more than 100 times, may persist for years. If hydromagnesiteis precipitated, it should convert to magnesite more or less rapidly (from a geologicstandpoint) in a wet or moist environment, but whether supersaturation with respectto magnesite can be sensibly reduced by contact with magnesite formed in this wayis doubtful.

There is also no evidence that waters from which some form of dolomite preci-pitates become less supersaturated with respect to this mineral. As will be explainedbelow, an apa of 10"1'1-00, roughly the K$v for protodolomite,. probably can bemaintained under certain conditions.

The possibility of long-term metastable persistence of calcite supersaturation isnot unequivocal. It was mentioned above that cave waters in limestones and dolomites,which arc characterized by relatively high Pco2 values, low ionic strengths, slightseasonal fluctuations in temperature, and simple compositions (largely Ca"1"*, Mg+"",and HCO3 ions), do tend to reduce their supersaturation and equilibrate with pure,coarse calcite. This tendency is not noted in the much more dynamic environment ofthe alkaline soda lakes. Pcoa values in these lakes are similar to that of the atmosphere;there are seasonal temperature fluctuations and variations in the rate of supply ofdissolved matter; ionic strength is moderate to high (0.02-0.5 and even higher); andaqueous sodium is much greater than calcium or magnesium, although aqueousmagnesium is somewhat greater than that encountered in dolomite cave water.

46

The waters of Neusiedlcrsee-Podersdorf, on the Austrian salt steppes, offer com-pelling evidence of persistent calcitc supersaturation. Both calcite andprotodolomiteare precipitating in this lake (35). According to Knic (23) the lake, although 320 squarekilometers in extent, averages only 4 feet in depth, and the whole steppe area is charac-terized by strong winds and high evaporation rates. Under such conditions the lakewaters probably are thoroughly mixed.

Four separate analyses (see table 1) of the lake water in summer months indicateconstant, uniform supersaturation with respect to both calcite and dolomite. In thewinter, though, with pH conditions nearly identical with those of the summer (8.84 vs.a summer average of 8.87) (2a), the calcium content of the lake water increases by afactor of 1.7, which is just about what one would expect from the increased solubilityof calcite near O"C (25). Aqueous magnesium shows no corresponding increase.Furthermore, analyses of the lake water during the time of spring rains (-3), withconcomitant dilution of lake water and lowering of pH (about 0.3 pH units), indicatea further increase in aqueous calcium, although the concentrations of all other aqueousconstituents, including magnesium, are diluted to about 65-70 percent of their Januarylevel. This behavior strongly suggests that the shallow and well-mixed waters ofNeusiedlcrsee do tend to seasonally equilibrate with primary calcitc and, during thesummer months only, with primary protodolomite. This calcite, however, must havea much greater free-energy than that determined for pure, well crystallized materialbecause of the uniform supersaturation (6 times to 9 times) of the lake water duringthe entire year. Other relatively shallow lakes from which both calcite and dolomite(or protodolomite) are precipitating indicate virtually identical activity products forcalcite and dolomite. Examples arc Balkhash, U.S.S.R., Borax Lake, California, andLake Kingston, South Australia.

It is tempting to appeal to a high magnesian content in the primary calcites ofthe above lakes as being the principal reason for higher and apparently persistentsolubility. Although there is a lack of chemical analyses for such calcites (physicalseparation from very fine grained dolomites and clay minerals is exceedingly difficult),Skinner (3fl) has used the X-ray cell-edge technique of Graf and Goldsmith (I(i) toshow that the primary calcites of Lake Kingston and adjacent lagoonal environmentscontain 16 to 22 percent MgCOs,. Recently Chave and others (7) have demonstratedby two different experimental methods that the solubility of skeletal marine calcitesincreases with increasing MgCOs, content. In the range of 15-25 percent MgCOs,,solubility increases from about 3 to about 10 times that of pure, coarse calcite. Theindicated supersaturation of the Lake Kingston sample (table 1) with respect to calciteis 8.3 times.

It seems likely that extensive ionic substitution may also increase the solubility ofprimary dolomite and even hydromagnesite. Skinner (3S) found that the protodolo-mite of Lake Kingston contains 56 percent CaCOa,. In addition to metastable ionicsubstitution, greater surface energy due to fine grain size and crystal defects or dislo-cations (for example, the random positioning of Ca and Mg atoms in protodolomite)should also play an important role in increasing carbonate solubility. For alkaline sodalakes these factors presumably account for the seemingly high degree of supersaturationnecessary for carbonate precipitation, but, as indicated above for Neusiedlersee, thesewaters arc probably not supersaturated with respect to the very fine grained nonstoi-chiometric carbonates that actually are precipitated. Persistence of these metastablecarbonates below the sediment-water interface (as much as 3 feet for the magnesiancalcites and calcian dolomites of Lake Kingston and nearby lagoonal environments(36)) tends to confirm this suggestion. In a similar vein Schmalz and Chave (34) suggestthat nearshore Bermuda marine waters also tend to equilibrate with the most soluble,highly magnesian calcite present in the sediment.

The alkaline soda lakes are more or less intermediate between cave water andocean water with regard to ionic strength and aqueous magnesium content, but are

47

as effectively supersaturated with respect to both calcite and aragonitc as cither (at25"C, aragonite is about 13 percent more soluble than calcite (13)). Aragonite, com-monly encountered in caves and warm-water shallow ocean sediments, is apparentlyrare in alkaline soda lakes. The formation of aragonite rather than calcite in cavesmay be due to a rapid release of CO2 to cave air, but the mechanisms that triggerprecipitation of inorganic aragonite in ocean water are poorly known (see, for instance,the discussion in Cloud (8), p. 103-105) Whatever these mechanisms may be, thenonformation of aragonite and the abundance.of primary, highly magnesian calcitein alkaline soda lakes suggest that the mechanisms are not related to a high Mg/Caratio in solution or to a lower solubility for aragonite than for magnesian calcite.

REFERENCES

(!) ALDERMAN, A. R., and SKINNER, H.C. W., (1957) : Dolomite sedimentation in thesouth-east of South Australia : Am. Jour. Sci., Vol. 225, No. 8, p. 561-567.

(2) ALDERMAN, A.R., and VON DER BORCH, C.C., (1960) : Occurrence of hydromag-nesite in sediments of South Australia : Nature, Vol. 188, No. 4754, p. 931.

(3) ALDERMAN, A.R., and VON DER BORCH, C.C., (1961) : Occurrence of magncsite-dolomitc sediments in South Australia : Nature, Vol. 192, No. 4805, p. 861.

(4) ALLAKVERDIEV, Sh. I., (1958) : Carbonates from the weathered crust of ultrabasicrocks of A7.erbaid7.han : lzv.Akad.Nauk. AzerbaklzhanS.S.R.,Ser. Geol.-Geograf.Nauk., No. 3, p. 79-87 (in Russian).

(5) BARON, G., and FAVRE, J., (1958) : Etat actuel des rccherches en direction de lasynthese de la dolomie : Rev. Inst. Francois Petrole et Annales Combustibles Liqui-des, Vol. 13, p. 1067-1085.

(6) BOND. G.W., (1946) : A geochemical survey of the underground water suppliesof the Union of South Africa : Union South Africa Dept. Mines, Ceol. SurveyMem., Vol. 41, p. 1-208.

(7) C H A V H . K . E . , DEFFEYES, K.S., WEYL, P. K., GARRELS, R. M., and THOMPSON, M.E.(1962): Solubility of skeletal carbonates in aqueous solutions : Science, Vol. 137,No. 3523, p. 33-34.

(8) CLOUD, P.E., Jr., (1962) : Environment of calcium carbonate deposition west ofAndros Island, Bahamas : U.S. Geol. Survey Prof. Paper 350, 138 p.

(9) C0CKHE1.D, W.E., and WALKER, J .F. , (1933) : An occurrence of magnesite nearClinton; British Columbia : Canada Ceol. Survev Summary Rept., 1932, pt. A-2,Pub. 2333, p. 72-73.

(10) COLEMAN, R.G., and WHITE, D.E., (1955 and 1958) : written communication.( n ) CUMMINGS, J. lyf., (1940) : Occurrences of hydromagnesite in British Columbia,

Chap. 3 of Saline and hydromagnesite deposits of British Columbia : BritishColumbia Dept. Mines Bull. 4, p . 102-129.

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