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 Eugsterite,NaoCa(SOa)3 ' 2HrO is a new salt mineral. It occursin diferent parts of Kenya and in the Konya Basin in Turkey. It is associatedwith one or more of the following miner- als: halite, thenardite, bloedite, gypsum, glauberite and nesquehonite.Eugsterite is mono- clinic, 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". Introduction It is seenat two placesalong the shoreof Lake Victo- and Luanda, where it is found as a sur- A salt mineral which showed an unknown X-ray ria, at Sindo with thenarditeand halite diffraction pattern was discoveredduring a study of face mineral in association (Table found at Kalacha, Turkana dis- the mineralogy of saline soils in Kenya and Turkey. l). It is also Desertin the north of Kenya. The same mineral was also found in salt eflores- trict, eastof the Chalbi occur and eugsteriteis cenceson bricks. The mineral is called "eugsterite" There vast salt eflorescences 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 Konya Basin in material is depositedat the National Museum of Ge- Salt sampleswere taken in the of 1978. Groundwater ology and Mineralogy, HooglandseKerkgracht 17, Turkey during the summer the samesites. The Konya Ba- Leiden. the Netherlands.The mineral and the name sampleswere taken at on the Central Anatolian Plateau were approvedby the Commissionon New Minerals sin is situated Ankara. This basin, a former and Mineral Names, IMA, prior to publication. about 300 km south of lake formed during the Tertiary, consistsof salt-af- Occurrence fectedclayey marl soils(de Meester,1970). The basin is bordered in the north by paleozoicschists and ig- Kenya 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 Permo- originated through evaporation have been sampled carboniferouslinestones and schistsand Cretaceous during the autunn of 1977in someregions in Kenya limestones.In and around the basin many Mio-Plio- (Vergouwen,Ph.D. thesisin preparation).Most salts cenevolcanoes of andesiticcomposition exist. belong to the group of sodium carbonatesand the Severalrivers flow into the basin, especiallyfrom waters are mainly of the Na-COr-SOo-Cl- or Na- the Taurus mountains. In the basin itself some ther- COr-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 found belong to this latter type (Fig. l). parts of the basin which are not flooded,salts form at Eugsteritehas been found in two different regions. the surfacethrough' evaporation of the groundwater. 0003-004x/8l /0506-0632$02.00 632 VERGOUWEN: EUGSTERITE 633 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 energy-dispersivesystem established that Na, Ca and chlorides of sodium and magnesium. Sodium car- S are the major components.The mineral was syn- bonates were found only at a few localities; these are thesized,because the naturally-occurring eugsterite devoid of eugsterite,which is commonly found in the always occurs with other minerals and becausethe other efrorescences.It occursin the following associ- grain size was very small (Fig. 2). ations: eugsterite,halite, thenardite; eugsterite, Solutions of sodium sulphate and gypsum were bloedite;eugsterite, halite, gypsum;eugsterite, halite, evaporatedon a water bath of 60oC and eugsterite glauberite; eugsterite,halite, glauberite, thenardite, formed in considerable amounts in solutions with a nesquehonite.This last associationwas found around molar ratio Na/Ca > 4 togetherwith thenardite and the historical medicinal spring of Tiana. The analy- gypsum.Eugsterite did not form from the samesolu- sesof the watersat the sitJs*[ere eugsteritehas been tions at room temperature.Thenardite and gypsum found are plotted in Figure l. Type locality occursat could be separatedwith a heavy liquid with d : 2.50. the playa northeastof the village of Karapinar which Eugsterite occurred both in the heavier fraction to- is situatedalong the main road from Konya to Eregli. gether with thenardite and in the lighter fraction to- In summer this playa is covered with a flinty white getherwith gypsum becauseof its sticky character. salt crust which consistsof halite, thenardite and eug- The tiny eugsterite fluffs were separated from the sterite. fraction with gypsum by handpicking under a binoc- ular. The gypsum contamination of the samples Bricks (sample size approximately I mg) was determined Eugsteritehas been found in salt eflorescenceson with the aid of a DTA apparatus. These samples bricks of Dutch river clays in association with gyp- showed in addition to the large endothermic peak of sum. Chemicalanalysis Table l. List of minerals usedin text In order to determinethe compositionof eugster- bloedite NarMg(SOa) ite, since the minute amounts of material available 2.4H20 precluded conventional chemical analysis, a prelimi- eugsterite Na.ca (SoO) 3.2H20 nary investigation was made by DTA. A natural glauberite NarCa(SOO) sampleof eugsteritewith thenarditeand halite shows , gyPsun CaSOO.2HTO a sharp endothermic reaction between 165o and 185'. A Mettler TA 2000 B DTA apparatus was ha1i te NaCl used.The reactionproduct containedglauberite so it hydroglauberite Na, (S0O),. 6ttro OCa, seemedlikely that eugsterite could be a sodium-cal- nesquehonite MeCOr.3HrO cium-sulphate-hydrate.In addition, quattative anal- thenardite NaTSOO ysis with an electron microscopeequipped with an VERGOUWEN: EUGSTERITE 4 -d at*-_ ' ...1.4::!,:.:.';'' .-, 'i.' Fig. 2. (a) SEM picture ofnatural eugsterite together with halite; (b) Synthetic eugsterite needle indicating the monoclinic character. eugsteriteonly very small negligible gypsum peaks. were large enough to analyzesulphate as well. Sul- Na- and Ca-contentof the sampleswere analyzedby phate was analyzedturbidimetrically. Results of an atomic absorption.Sulphate could not be analyzedas analysisare given in Table 2. Combination of these well becauseof small samplesize. two sets of analysesleads to the ideal formula From the fraction of eugsterite with thenardite, NaoCa(SOo)3'2H,O. weight lossafter heatingwas determinedwith a TGA apparatus(Dupont TA 990). In this fraction all Ca X-ray crystallograPhY and HrO belongsto eugsteriteso the HrOlCaO ratio The X-ray diffraction pattern (Table 3) was deter- of eugsterite could be determined. These samples mined for svnthetic material as these films were VERGOUWEN: EUGSTERITE Table 2. Chemical analysesof samplesof synthetic eugsterite.The Table 3. X-ray di-ffraction powder pattern of synthetic eugsterite. DTA samplescontain a negligible amount of gypsum.The TGA Line positions measuredby Dr. J. W. Visser at the Technisch samplescontain thenardite Fysischc Dienst at Delft using a Guinier camera wittr CuK"l radiation,l, : 0.15406nm, and a specialdensitometer for Guinier DTA smples films -? -? -? Namol 9,l5xl0' 9.0 xl0' 9.l5xl0' -1 -?- t2,62 I 1.9431 4 Ca mol 2.33 x f0 " 2.25 x lO L.)J X IU 9.20 39 1.9291 2 6.32 4 1,9t99 <l Na/ca 3.93 4 ? o? 5.96 I 1.908r <l 5.50 64 l .8935 <l TGA samples 5.35 I r .8835 4.64 5 | .8494 4.60 5 r .8406 Na mol 0.150 0.019 4.58 8 I.83r3 4. 50 33 I.8t25 Ca mol 0.0226 0. 0045 4.20 4 | .7998 S0O mol 0. l0 0.0138 3.860 l 1,7922 3.8r9 t.7648 H2O mol 0.049 0,0087 3.622 3 | .76t9 3.590 2 | .7213 H2o/c^ 2. t6 r .93 3.454 32 t.7126 6l 3.428 r00 | .6999 4 3.233 + l .6809 5 much less complicated than the films of the natural 3.2t1 t0 | .6632 o occurrences.Only the pattern of thenardite or gyp- 3.150 4 I .6530 4 sum had to be subtracted.The line positionsof natu- 3.1l8 <l | .6459 <l ral eugsteriteagree exactly with those of synthetic 3.065 l5 l.6r98 3 eugsteriteand comparisonof many nlms 3.054 6 l .6053 2 showedno 2.973 2 l .590| I shift of lines at all. 2.936 t6 t.5829 2 It has not beenpossible to calculatethe unit cell by 2.893 8 1.5523 3 meansof the powder data. With a computerprogram 2.797 t9 1.5418 <r (Visser, 1969) many solutions were obtained but 2.763 25 I .5318 <I 2.746 46 t.5234 <l none was very satisfactory.Efforts to grow larger 2.727 8 1.5148 2 crystalsfor a single-crystalanalysis did not succeed. 2.61| t3 r .5046 <l 2.545 | .4963 3 Morphology,crystallography and physicaland 2.458 5 1.4645 I 2.291 5 t.4599 <l optical properties 2.284 2 t.4536 I The mineral forms clustersof thin fibers. The nat- 2.231 2 t.4293 2 urally-occurring fibershave a thicknessof 0.5-1.5pm 2.2t4 2 | .4t78 3 2.