American Mineralogist, Volume63, pages 715-719,1978
Sarabauite,a newoxidesulfidemineralfrom the Sarabaumine,Sarawak,Malaysia
Izum Neret
Departmentof Chemisty, The Uniuersityof Tsukuba
Sakurq-mura,I baraki 300-3l, Japan
Hnrtur AolcHI
Nihon Seiko Company,Ltd.,2 Shimomiyahi-cho
Shinjuku,Tokyo 162,Japan
SerossrMersugenn,AKIneKeto
Departmentof Geology,NationalScienceMuseum
3-23-l Hyakunin-cho,Shinjuku,Tokyo 160,Japan
Funwlnn
KezuNosurn Mesuroul, TAKASHI
KarasumaDemizuNishiiru, Kamikyo, Kyoto 602,Japan
eNn Kozo Ne,cnssIl,ur
Depqrtmentof Chemisty, The Uniuersityof Tsukuba
Sakura-mura,Ibaraki 300-3I, Japan
Abstract
Sarabauite,CaSb,oO,oS.,
is a new mineralfound at the Sarabaumine, about 40 km S{ of
Kuching, Sarawak,Malaysia. It occurs as small realgar-likemassesin vein-like mineral
aggregates
composedof quartz,calcite,wollastonite,stibnite,and minor senarmontitein an
altered limestone.It is probably a product of primary hydrothermalmineralization.The
mineralismonoclinic,spacegroupC2/c,a:25.37(2),b=5.654(l),c:16.87(l)A,B=
117.58(4)', and Z : 4. The strongestX-ray powder lines are 3.215(100X514),
2.817(88X020,5r2.-406,800).3.466(78X312),3.182(60)(5il),3.164(s0X802),4.227(42)(ffi2),
2.583(40)(421).
It has a realgarJikecarmine-redcolor, resinousluster, and orange streak.
Cleavageis not observed.Vickers microhardness(20 g load) is 272+6 kg/mm'. Specific
gravity is 4.8 (meas.)and 4.99 (calc).Under the ore microscopeit is gray with brownishto
purplishpleochroiccolorsand hasstrongreddish-orange
internalreflections.The reflectances
nm,
percent;546nm, 24.7-19.7
percent;589nm, 23.5-19.1percent;656
are:486nm, 25.8-20.1
ElectronmicroprobeanalysisgaveCa
20.0-14.0percentfor maximaand minima respectively.
It is
to Ca".rrSbroOr.r.Su.o..
2.43,Sb 74.89,O9.61,S 11.91,total 98.84percent,corresponding
readily soluble in conc. HCI with evolution of HrS and slowly in conc. NaOH and dilute
under hydrothermalcondiHNO, solutions.Singlecrystalsof sarabauitewere synthesized
tions: 500oC,1000kglcm'?.
Introduction
A realgar-like carmine-red mineral was found in
hydrothermal ore deposits of the Sarabau mine, Sarawak, Malaysia. After microprobe analysis and synthetic work, the mineral proved to be a new species
having the ideal chemical formula CaSb'oO'.S..This
ow3-N4X/78/0708-0715$02.09
is the second naturally occurring oxide sulfide mineral, kermesite (SbrSrO) being the first.
The mineral is named sarabauite after the locality.
The mineral and the name have been approved by the
Commission on New Minerals and Mineral Names,
IMA.
715
7t6
NAKAI ET AL: SARABAUITE, A NEW MINERAL
age.The habit is tabular and prismaticparallelto the
6 axis.The specificgravity measuredby Bermanbalanceis 4.8, while the calculatedvaluefrom the theoretical formula is 4.99. Vickers microhardnessis
272+6 kg/mm2(load20 g). The mineralis not brittle
but is to someextentsectile.
Under the ore microscopeit is gray-white with
discerniblereflection pleochroismchangingfrom a
brownish to a purplish tint. Internal reflectionsare
quite remarkablewith reddish-orange
color. No polishing cleavageis observed.The reflectances
are:486
nm,25.8-20.1percent;546 nm, 24.7-19.7percent;
589nm, 23.5-19.1percent;
656nm, 20.0-14.0
percent
SARABAU
MINE
J/
for maxima and minima respectively.Thesefigures
'/
20 kn
may be affecteddue to internal reflections.
Owing to its extremelystrongabsorption,verylimFig. l. Locationmap of the Sarabaumine,Sarawak,Malaysia.
ited optical propertiesfor transmittedlight wereobtained.The samplesusedweresyntheticCaSbroO,oS..
Description
It is opticallybiaxialnegativewith 2V about90o,| :
The ore depositsof Sarabaumine arelocatednear Y, and the pleochroismis from reddish-yellow
(lly)
Bau,about40 km SW of Kuching,Sarawak(Fig. I ), to brownish
-red(llZ').
where limestone,shale,chert, sandstone.and conglomeratebelongingto the Bau Seriesof Upper JuX-ray crystallography
rassicto Cretaceousare exposed.They are locally
The precessionand Weissenbergphotographic
intrudedby microdiorite,microtonalite,dacite,and studiesshowedthe mineral to be
monoclinicwith
quartz-andesiteof late Tertiary age,and the volcanic possiblespacegroup
either Cc or C2/c. The latter is
activity is consideredto be responsiblefor the miner- preferredaccordingto the resultsof a structural
analalization of gold, silver, antimony, and mercury ysis (Nakai et al., 1977).The
unit-cell parameters
found in the rocksof the Bau Series(Wilford, 1955); refined with a four-circle
automatic diffractometer
very probably the formation of the Sarabaudeposits (MoKa, = 0.7092584)arca =
25.37(2),b=5.654(l),
was due to the samegeologicevent.
:
p
c = 16.87(l),4'
and
117.58(4)".
Only one specimenshowing the mode of occurIn the sarabauitestructure(Nakai et al., 1977),the
renceof sarabauitewas found. All descriptions
and
studieswere made on this material. It is a piece of
gray fine-grainedlimestonecut by a sarabauite-bearing vein-likebody more than 5 cm in width. The
modeofoccurrences
ofsarabauiteand the associated
mineralsincludingstibnite,wollastonite,
quartz,calcite,and minor senarmontitearedepictedin Figure2.
Sarabauiteforms long tabular crystalselongated
along the b axis, and the maximum length reachesI
mm. A well-developed
externalshapewasonly occasionallyobservedunderthe ore microscope;however,
evenso, the morphologycould not be determined.
The closeassociationof stibnite,senarmontite,and
sarabauitesuggeststhe absenceof any stablephases
with intermediatecompositionsbetweenCaSb,oO,o
S.-SbrSB-SbrOs
under the conditions of sarabauite
formation, which excludedthe formation of kermesite.
Physicaland optical properties
Fig. 2. Sketchof the studiedsarabauite-bearing
specimen.Sa:
Sarabauitehas a realgar-likecarmine-redcolor. sarabauite;Sb: stibnite(with minor
senarmontite):
Wo: wollastoresinousluster, orange streak,and no visible cleav- nite; Ct: calcite.
717
NAKAI ET AL: SARABAUITE, A NEW MINERAL
Sb atoms are coordinatedby threeO and/or S atoms
to form trigonalpyramidsof SbO3,SbSgand SbSrO.
The SbOg pyramids compose4-memberedand 8memberedSb-O rings.Thesetwo rings link by sharing a cornerO atom to form a chainparallelto [001].
On the other hand,two SbS3and two SbSrOpyramids form an 8-memberedSb-S ring. Moreover the
8-membered
Sb-O and Sb-S ringslink by sharinga
cornerO atom to form a chainparallelto [101].As a
whole, thoselinkagesof ring structuresgive rise to a
network parallelto (010).The Ca
two-dimensional
atom is sandwichedbetweenthe two 8-membered
Sb-O ringsand forms a CaOepolyhedron.Thus the
Ca atomslink the networksin the b-axisdirection.
Kermesite(SbrSrO)is the only mineral which is
compositionallyrelatedto sarabauite.However,kermesitecontainsno cationother than antimony,and
this givesa certaindifferencebetweenthe two structures.The kermesitestructure(Kup6ik' 1967)has a
similar network composedof Sb, S, and O atoms
parallelto (100).As mentionedabove,in sarabauite
the nets are linked by the Ca atomsto form a threedimensionalstructure,whereasin kermesitethe nets
are stackedin the a axisdirectionand linked by weak
Sb-S and Sb-O bonds. The averagebond distances
are:Ca-O 2.467,9b-O2.000and Sb-S2.4654.Similar valuesare observedin kermesiteaswell asin other
oxidesand sulfides.
The X-ray powder patternobtainedby the diffractometer method using Ni-filtered Cu radiation is
givenin Table l. The indexingwasmadeon the basis
of single-crystaldata. There is good agreementbetween intensitiesof the X-ray powder and singlecrvstaldata.
Table l. X-ray powder diffraction data for sarabauite*
hkl
200
202
1II
5La
602
II3
5L2
600
004
JLZ
314
5r4
5tr
802
712
7].3
d calc
II.24
8.224
4.970
4.452
3.915
3.751
3 . 74 8
3.738
3.45r
3.379
3 -207
3.L79
3.155
3.0s0
/ ro
9r5
2.50L
020
)La
406
800
22r
zuo
tL)
404
r 0 . 0 .4
006
a't )
910
1 0. 0 . 0
604
7r7
6Za
vz)
fi. r. r
II.I.O
820
lro
zzo
f d . o .s
6.4t0
20
6
4.979
4.462
4.227
3.924
3 . 74 8
36
42
30
15
{OO
3.385
3.215
3.L82
3.r64
3.052
3.OII
2.970
2.8L7
Z.LUO
2.054
2.02r
2,001
1.993
q7?
r.957
r.947
* Cu/Ni radiation,
**b: broad
1r.33
o
d
78
10
100
60
50
6
5
5
88
2-753
zv
z.
z6
tL6
2.544
2 .607
2.583
2.503
2.498
2.409
2.365
2.329
2.28L
2.251
2.r87
2. r08
2.058
2.023
2.004
1
00(
L.976
r.950
L.Y>Z
diffractotneter
9
t8
40
I4
15
r.922
1.888
1.888
1,859
r.859
1. 859
l. 834
oz
L .6Z0
I
r33
1.80s
I.79]1.780
lro
r.
3L7
oz+
531
12.2.5
732
823
733
734
10.0.4
5.1.t0
318
1.751
1.730
L.692
rJ . r. o
D
5
5
5
t2
L3
methodl, 0.5o min
/lo
r.o/l
d obs
l/lo
r.922
r.890
15
22
L.872
18b
r.830
15b
1.808
T.79L
r.783
r.756
7
t2
13
1.731
L.694
L.673
8
I8
TD
ID
1.672
r.o/r
r.655
1.538
L.623
r.501
r.578
r.ooo
f,
1.640
L.620
1.503
2
8
9
8b
t.
)6u
r.)/6
, f o
l(
I
L.5TZ
7
L>.L.2
935
LU.2-9
9
5
20
5
4b* *
4b
16
29
calc
10.0.2
825
I0.2.3
026
623
804
lI8
L32
2.327
2.285
2.249
2.188
2-L70
I
Ll Lo
J.
J.UU /
2.970
2.827
2.816
2.8rf
2. 81r
2.752
2.7L3
2.639
2.606
2.580
2.507
2.492
2.40L
I LL
d obs
1 3. 1 . t 0
f,ld
1.569
1.559
a.)zo
I.5L2
1.483
L.448
I.+5J
04r
44L
542
7L8
f 3 .r . r
2.o.tz
irs
ta.2.7
F.n.s
r.407
r.379
L.377
1.34r
1.340
r .326
r.308
1.306
r.269
L.252
r.235
1. 571
5b
1.550
I.524
1.515
r.483
1.450
L.432
L. 407
1.379
11
L.342
9
1.328
r. 310
2
5
r.270
r.250
L.236
ID
IL
I
o
J
5D
4b
f,
f
4
718
NAKAI ET AL: SARABAL]ITE, A NEW MINERAL
Table 2. Electronmicroprobechemicalanalysisof sarabauite
molecuLar
quotient
t.
Ca
5D
o
D
Total
I.
2.
?
2.43
74 . 8 9
9.61
II.91
9.72
12.05
9 8 .8 4
100.00
Sarabauite,
Sarabauite,
Theoretical
2 .46
ta.I
Sarabau mine,
normalized
to
CaShoeoSe,
0.0514
0.6223
0.6075
0.3759
I
mole number
(basis
Sb=10)
0.99
l0
9.76
6.04
ideal
number
3.
I
10
10
6
2.49
75.62
9.94
11.95
r00.00
Sarawak,
I00t.
Malaysia.
Chemicalcompositionand properties
The electronmicroprobeanalysisusing JXA-5A
analysergave the resultsshown in Table 2. Wavelengthscansdisclosed
only Ca, Sb,O, and S in major
amountsand other elementswere not found. The
standardsusedwere stibnite,kermesite,valentinite,
and wollastonite.
Measurements
weremadeat 25 kV
for Ca, Sb, and S, and 15 kV for O. The result
calculated
on the basisof Sb : l0 leadsto theempirical formula Cao.rrSbroOr.ruS..on.
From the measured
s p e c i f igc r a v i t y , Z : 4 .
The mineraldecomposes
readilyin conc.HCI with
evolutionof HrS and veryslowlyin conc.NaOH and
dilute HN03 solutions.
Thermalstudy
Thermal analyseswere performedwith a heating
rate of 2.5"C/min. The DTA and TGA curvesare
characterized
by a strongexothermicpeak at about
420" with a weight loss and a weak one at about
490"C. The corresponding peaks for synthetic
CaSb,oOroSu
are found at 410" and 490oC,respectively. X-ray powder study of the product after thermal treatmentat 490oCrevealedthat it consistsof a
mixture of cubic Sbros, Sb2O4,and CaSbzO..The
latter two compoundssurvive in the product at
1000.c.
Synthesis
Stoichiometric CaSbroO,sS6
was hydrothermally
synthesized
from CaO:SbzS,
: Sb2O,: I : 2: 3 mixture
in both cold-sealstellitebombs and silica tubesat
temperaturesfrom 230 to 560.C under pressures
from 30 to 1500kg/cm". The reactionrate is so rapid
that the formationrequiresonly one hour at 500"C
and 1000kg/cm". Although it includessmall fractions of recrystallizedacicular Sb2S,and polygonal
SbrO, (either cubic or orthorhombic)in someruns,
the product, including singlecrystalsup to 3 mm
elongatedalong the b axis, consistsof aggregates
of
carmine-redtablets having the same appearance,
habit, and luster as the natural mineral.A scanning
electronmicrographof the syntheticcrystal is given
in Figure3.
SyntheticCaSb,oOroSu
is madeup of at leasttwo
morphologicallydifferentcrystals,columnarand tabular. They are elongatedalong the D axis like the
natural crystals,and the latter are characterized
by a
well-developed
{100}form.
Acknowledgments
Fig. 3. Scanning electron micrograph of synthetic CaSb,oOroSu.
We wishto thank Mr. K. Hirata,T. Okumura,and y. Kondo of
ElectronOptics Division, Jrol Ltd., for invaluablehelp with the
NAKAI ET AL: SARABAUITE, A NEW MINERAL
We expressappreciationto Mr. K.
electronmicroprobeanalyses.
Ogawaof Departmentof Mineral Industry,Schoolof Scienceand
Engineering,WasedaUniversity, Tokyo, for measurementof re'
Thanks are alsodue to ProfessorS. Kanno of Departflectances.
ment of Geoscience,The University of Tsukuba, for information
about the geologyin the vicinity of the Sarabaumine.
Nakai, L, K. Koto, K. Nagashimaand N' Morimoto (1977)The
a new oxide sulfide
crysial structure of sarabauiteCaSbroOroSo,
6'
5-27
(Japan),
27
mineral. Chem.Lett.
Wilford, G. E. (1955)The geologyand mineralresourcesof the
Kuching-Lunduarea,West Sarawak,includingthe Bau Mining
District. Geol. Suru.Bomeo' Mem. 3.
References
Kupbik, V. (1967) DiE Kristallstruktur des Kermesits'SbrSrO'
54, | 14.
Nalurwissenschaften,
7t9
Manuscripl receiued,Febtuary 18,1977' accepted
for publication,February9' 1978'