American Mineralogist, Volume 66, pages 632-636, 1981 Eugsterite,a new salt mineral LronrB VBRcouwnN Departmentof Soil Scienceand Geology Agricultural University, Duivendaal I 0 Wageningen,The N etherlands Abstract ' 2HrO is a new salt mineral. It occursin diferent parts of Kenya Eugsterite,NaoCa(SOa)3 and in the Konya Basin in Turkey. It is associatedwith one or more of the following minerals: halite, thenardite, bloedite, gypsum, glauberite and nesquehonite.Eugsteriteis monoclinic, B : I 16o.The strongestX-ray ditrraction lines are (d ta A (intensity)): 9.20 (39), 5.50 (64),4.50(33),3.454(32),3.428(100),2.763(2s),2.746(46), r.7126(61).It forms clustersof thinfibers.Refractiveindices1.492<a,B,y=1.496;birefringence:0.004,tllb,Bc: 27". It is seenat two placesalong the shoreof Lake Victoand Luanda, where it is found as a surA salt mineral which showed an unknown X-ray ria, at Sindo in associationwith thenarditeand halite face mineral diffraction pattern was discoveredduring a study of (Table l). It is also found at Kalacha, Turkana disthe mineralogy of saline soils in Kenya and Turkey. in north of Kenya. The same mineral was also found in salt eflores- trict, eastof the Chalbi Desert the occur and eugsteriteis vast salt eflorescences There cenceson bricks. The mineral is called "eugsterite" with halite and thenardite. after Hans P. Eugster,The Johns Hopkins Univer- found in association sity, Baltimore, Maryland, who has extensivelystud- Turkey ied the origin and mineralogy of saline lakes. Type Salt sampleswere taken in the Konya Basin in material is depositedat the National Museum of GeTurkey during the summer of 1978. Groundwater ology and Mineralogy, HooglandseKerkgracht 17, were taken at the samesites.The Konya Basamples Leiden. the Netherlands.The mineral and the name on the Central Anatolian Plateau is situated sin were approvedby the Commissionon New Minerals km south of Ankara. This basin, a former 300 about and Mineral Names, IMA, prior to publication. lake formed during the Tertiary, consistsof salt-affectedclayeymarl soils(de Meester,1970).The basin Occurrence is borderedin the north by paleozoicschistsand igKenya neous rocks covered by mesozoic limestones.The Salts of saline soils with efrorescencesat the sur- Taurus mountains form its southern border. They face and groundwatersfrom which these salts have consist of ultrabasics, Devonian and Permooriginated through evaporation have been sampled carboniferouslinestones and schistsand Cretaceous during the autunn of 1977in someregionsin Kenya limestones.In and around the basin many Mio-Plio(Vergouwen,Ph.D. thesisin preparation).Most salts cenevolcanoesof andesiticcompositionexist. Severalrivers flow into the basin, especiallyfrom belong to the group of sodium carbonatesand the waters are mainly of the Na-COr-SOo-Cl- or Na- the Taurus mountains.In the basin itself some therCOr-Cl-type (Eugster and Hardie, 1978). In some mal springs occur. The climate is semi-arid with cold samplesites,however,the groundwatersare carbon- moist winters and hot dry summers.The lowestparts ate-poor and they are of the Na-SO.-Cl-type. The are flooded in winter and when the surface water groundwatersof the places where eugsteritewas evaporatesin sumner vast salt crustsoccur. [n other parts of the basin which are not flooded,saltsform at found belong to this latter type (Fig. l). Eugsteritehas been found in two different regions. the surfacethrough'evaporationof the groundwater. 632 l /0506-0632$02.00 0003-004x/8 Introduction 633 VERGOUWEN: EUGSTERITE Fig, l. Composition (moIe Vo) of groundwaters at the localities where eugsterite has been found in the system Ca-Na+K-Mg-CI-SQa-HCO3+CO3 from the Konya Basin (Turkey) and from different regionsin Kenya. The salts in the'basin are mainly sulphates and chlorides of sodium and magnesium. Sodium carbonateswere found only at a few localities; these are devoid of eugsterite,which is commonly found in the other efrorescences. It occursin the following associations: eugsterite,halite, thenardite; eugsterite, bloedite;eugsterite,halite, gypsum;eugsterite,halite, glauberite; eugsterite,halite, glauberite, thenardite, nesquehonite.This last associationwas found around the historical medicinal spring of Tiana. The analysesof the watersat the sitJs*[ere eugsteritehas been found are plotted in Figure l. Type locality occursat the playa northeastof the village of Karapinar which is situatedalong the main road from Konya to Eregli. In summer this playa is covered with a flinty white salt crust which consistsof halite, thenardite and eugsterite. Bricks Eugsteritehas been found in salt eflorescenceson bricks of Dutch river clays in association with gypsum. energy-dispersive systemestablishedthat Na, Ca and S are the major components.The mineral was synthesized,becausethe naturally-occurring eugsterite always occurs with other minerals and becausethe grain size was very small (Fig. 2). Solutions of sodium sulphate and gypsum were evaporatedon a water bath of 60oC and eugsterite formed in considerable amounts in solutions with a molar ratio Na/Ca > 4 togetherwith thenardite and gypsum.Eugsteritedid not form from the samesolutions at room temperature.Thenardite and gypsum could be separatedwith a heavy liquid with d : 2.50. Eugsterite occurred both in the heavier fraction together with thenardite and in the lighter fraction togetherwith gypsum becauseof its sticky character. The tiny eugsterite fluffs were separatedfrom the fraction with gypsum by handpicking under a binocular. The gypsum contamination of the samples (sample size approximately I mg) was determined with the aid of a DTA apparatus.These samples showed in addition to the large endothermic peak of Table l. List of minerals usedin text Chemicalanalysis In order to determinethe compositionof eugsterite, since the minute amounts of material available precluded conventional chemical analysis, a preliminary investigation was made by DTA. A natural sampleof eugsteritewith thenarditeand halite shows a sharp endothermic reaction between 165o and 185'. A Mettler TA 2000 B DTA apparatus was used.The reactionproduct containedglauberiteso it seemedlikely that eugsterite could be a sodium-calcium-sulphate-hydrate.In addition, quattative analysis with an electron microscopeequipped with an bloedite gyPsun NarMg(SOa) 2.4H20 Na.ca (SoO) 3.2H20 N a r C a( S O O ) , CaSOO.2HTO h a 1i t e NaCl hydroglauberite nesquehonite (S0O),. 6ttro OCa, MeCOr.3HrO thenardite NaTSOO eugsterite glauberite Na, VERGOUWEN: EUGSTERITE 4 -d ' at*-_ ...1.4::!,:.:.';'' .-, Fig. 2. (a) SEM picture ofnatural 'i.' eugsterite together with halite; (b) Synthetic eugsterite needle indicating the monoclinic character. eugsteriteonly very small negligible gypsum peaks. Na- and Ca-contentof the sampleswere analyzedby atomic absorption.Sulphatecould not be analyzedas well becauseof small samplesize. From the fraction of eugsteritewith thenardite, weight lossafter heatingwas determinedwith a TGA apparatus(Dupont TA 990). In this fraction all Ca and HrO belongsto eugsteriteso the HrOlCaO ratio of eugsterite could be determined. These samples were large enough to analyzesulphate as well. Sulphate was analyzedturbidimetrically. Results of an analysisare given in Table 2. Combination of these two sets of analysesleads to the ideal formula NaoCa(SOo)3'2H,O. X-ray crystallograPhY The X-ray diffraction pattern (Table 3) was determined for svnthetic material as these films were VERGOUWEN: EUGSTERITE Table 2. Chemical analysesof samplesof synthetic eugsterite.The DTA samplescontain a negligible amount of gypsum.The TGA samplescontain thenardite DTA smples -? Namol 9,l5xl0' Ca mol 2.33 x f0 " -? 9.0 xl0' -1 Na/ca -? 9.l5xl0' - ?- 2.25 x lO 3.93 Table 3. X-ray di-ffraction powder pattern of synthetic eugsterite. Line positions measuredby Dr. J. W. Visser at the Technisch Fysischc Dienst at Delft using a Guinier camera wittr CuK"l radiation,l, : 0.15406nm, and a specialdensitometerfor Guinier films L.)J 4 X ? IU o? TGA samples Na mol 0.150 0.019 Ca mol 0.0226 0. 0045 S0O mol 0. l0 0.0138 H2O mol 0.049 0,0087 H2o/c^ 2.t6 r.93 much less complicated than the films of the natural occurrences.Only the pattern of thenardite or gypsum had to be subtracted.The line positionsof natural eugsteriteagree exactly with those of synthetic eugsteriteand comparisonof many nlms showedno shift of lines at all. It has not beenpossibleto calculatethe unit cell by meansof the powder data. With a computerprogram (Visser, 1969) many solutions were obtained but none was very satisfactory.Efforts to grow larger crystalsfor a single-crystalanalysisdid not succeed. Morphology,crystallographyand physicaland optical properties t2,62 9.20 6.32 5.96 5.50 I 39 4 I 64 1.9431 1.9291 1,9t99 1.908r l .8935 5.35 4.64 4.60 4.58 4.50 I 5 5 8 33 r .8835 | .8494 r .8406 I.83r3 I.8t25 4.20 3.860 3.8r9 3.622 3.590 4 l | .7998 1,7922 t.7648 | . 76 t 9 | . 72 1 3 3.454 3.428 3.233 3 . 2 t1 3.150 32 r00 + t0 3.1l8 3.065 3.054 2.973 2.936 <l 3 2 4 2 <l <l <l t.7126 | .6999 l .6809 | .6632 I .6530 6l 4 5 <l 2 t6 | .6459 l.6r98 l .6053 l . 5 9 0| t.5829 2.893 2 . 79 7 2 . 76 3 2.746 2 . 72 7 8 t9 25 46 8 1.5523 1.5418 I .5318 t.5234 1.5148 3 <r <I <l 2 2 . 6 1| 2. 5 4 5 2.458 2.291 2.284 t3 r .5046 | .4963 1.4645 t.4599 t.4536 <l 3 I <l I 4 l5 6 5 5 2 o 4 3 2 I 2 The mineral forms clustersof thin fibers. The nat2.231 2 t.4293 2 2 . 2 t4 2 | .4t78 3 urally-occurring fibershave a thicknessof 0.5-1.5pm 2. t78 2 t.4021 2 and they are up to 40 pm long. The synthetic fibres <l 2. t70 r .3869 I <l <l arc 2-6 p thick and up to 200 pm long (measuredon 2. t58 l .3820 SEM pictures, see Fig. 2). The mineral is colorless 2.148 2 | .3654 I and transparent,its hardnessis very low and it is sol2.132 2 r .3555 2 <l 2.t12 2 | .3470 uble in water. The density could not be measured 2.043 I l .3353 3 due to its sticky nature. In the heavy liquid with d : <l 2.O13 t.3299 7 2.50 the upper fraction consistsof mixtures of eug| .9837 2 1.3234 2 sterite and gypsum, whereas the lower fraction is | .9546 3 composedof eugsteriteand thenardite. The SEM picture of the synthetic material shows the symmetrymost probably to be monoclinic with B Discussion : 116o. Optically it is biaxial, but the axial angle could not be determined on account of the fibrous Eugsterite is a very common salt mineral which habit. Refractive indices 1.492< a, B, ^t < 1.496;bi- forms during evaporation of nonalkaline waters. The :0.004, n, ll D,B^c:27o. refringence mineral is synthesized easily at 600 while at room 636 VERGOUWEN: EUGSTERIT:E temperature it did not form. This may be an indication that it is a metastablemineral under natural circumstances. Hydroglauberiteis the only other known sodiumcalcium-sulphate-hydrousmineral. However, the Xray pattern. of hydroglauberite differs essentially from that of eugsterite(Slyusareva,M.N., 1969).An unknown sodium-calcium-sulphate-hydrate,called phaseX, has beenfound by L.A. Hardie, JohnsHopkins University, Baltimore, in Saline Valley and by R. C. Erd of the U.S. GeologicalSurveyin the Death Valley salt pan associatedwith glauberite,thenardite and gypsum (both from L. A. Hardie, unpublished Ph.D. thesis,Johns Hopkins University). This mineral was not chemicalTy analyzed, but Hardie assumedit to be the sameas what is known as "labile salt", a synthetic double salt (2NarSOo. CaSOo '2H,O) (Hill and Wills, 1938).No X-ray data are availablefor "labile salt". The X-ray powder diffraction pattern given to "labile salt" by Conley and Bundy (1959) is for thenardite, which is already notedby Braitsch(1971,p. 76). The line positionsof the X-ray powder pattern of Hardie's phaseX agree fairly well with that of eugsterite.There are, however, somediferences in intensities.It is very probable that eugsteriteis the sameas Hardie's phase X and as "labile salt". Acknowledgments I thank Dr. Akira Kato, Drs. E. L. Meijer and Dr. L. van de? Plas for their helpful suggestions,Mr. E. Velthorst, Mrs. A. Baas and Mr. J. D. J. van Doesburgfor the chemical analysis,Mr. F. Thiel for operating the SEM and Dr. J. W. Visser for measuring the X-ray powdcr pattern. Miss A. Bouter typed the manuscript. References Braitsch, O. (1971) Salt deposits,their origin and composition. SpringerVerlag, Berlin. Eugster,H. P. and L. A. Hardie (1978) Saline Lakes. In A. Lerman, Ed., Lakes: Chemistry, Geology and Physics. Springer Verlag, New York. Hill, A. E. and Wills, J. H. (1938) Ternary SystemsXXIV. Calcium sulfate, sodium sulfate and water. Journal of the American Chemical Society60, 164'l-1655. Meester,T. de (1970)Soilsof the Great Konya Basin,Turkey. Pudoc, Wageningen,the Netherlands. Slyusareva,M.N. (1969) Hydroglauberite,a rew mineral of the hydrous sulfate group. Zapiski Vsesoioznogo MineralogicheskogoObschestva98, 59-62. (In Russian). Visser,J. W. (1969)A fully automaticprogramfor finding the unit cell from powder data. Journal of Applied Crystallography2, 89. Manuscript received, Iuly 15, 1980; acceptedfor publication, January 5, 1981.
© Copyright 2024 Paperzz