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.