American Mineralogist, Volume63, pages 715-719,1978

Sarabauite,a newoxide sulfide mineral from 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, AKIne Keto Departmentof Geology,National ScienceMuseum 3-23-l Hyakunin-cho,Shinjuku, Tokyo 160,Japan

KezuNosurnMesuroul, TAKASHIFunwlnn KarasumaDemizu Nishiiru, 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, about40 km S{ of Kuching, Sarawak,Malaysia. It occurs as small realgar-likemasses in -like mineral aggregatescomposed of ,, , , 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-red color, resinousluster, and orangestreak. 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 purplishpleochroic colors and hasstrong reddish-orange internal reflections. The reflectances are:486 nm, 25.8-20.1percent; 546 nm, 24.7-19.7percent; 589 nm, 23.5-19.1percent;656nm, 20.0-14.0percent for maximaand minimarespectively. Electron microprobe analysis gave Ca 2.43,Sb 74.89,O9.61, S 11.91,total 98.84 percent, corresponding to Ca".rrSbroOr.r.Su.o..It is readily soluble in conc. HCI with evolution of HrS and slowly in conc. NaOH and dilute HNO, solutions.Single crystals of sarabauitewere synthesizedunder hydrothermalcondi- tions: 500oC,1000 kglcm'?.

Introduction is the second naturally occurring oxide sulfide min- A realgar-like carmine-red mineral was found in eral, kermesite (SbrSrO) being the first. hydrothermal ore deposits of the Sarabau mine, Sara- The mineral is named sarabauite after the locality. wak, Malaysia. After microprobe analysis and syn- The mineral and the name have been approved by the thetic work, the mineral proved to be a new species Commission on New Minerals and Mineral Names, having the ideal chemicalformula CaSb'oO'.S..This IMA. ow3-N4X/78/0708-0715$02.09 715 7t6 NAKAI ET AL: SARABAUITE, A NEW MINERAL

age.The habit is tabular and prismaticparallel to the 6 axis.The specificgravity measuredby Bermanbal- anceis 4.8, while the calculatedvalue from the theo- retical formula is 4.99. Vickers microhardnessis 272+6kg/mm2 (load 20 g). Themineral is not brittle but is to someextent sectile. Under the ore microscopeit is gray-whitewith discerniblereflection pleochroism changing from a brownish to a purplish tint. Internal reflectionsare quite remarkablewith reddish-orangecolor. No po- lishingcleavage is observed.The reflectancesare:486 nm,25.8-20.1percent; 546 nm, 24.7-19.7percent; 589nm, 23.5-19.1percent; SARABAUMINE 656nm, 20.0-14.0percent J/ for maxima and minima respectively.These figures 20 kn '/ may be affecteddue to internal reflections. Owing to its extremelystrong absorption, very lim- Fig. l. Locationmap of theSarabau mine, Sarawak, Malaysia. ited optical propertiesfor transmittedlight wereob- tained. Description The samplesused were synthetic CaSbroO,oS.. It is opticallybiaxial negative with 2V about90o, | : The ore depositsof Sarabaumine are located near Y, and the pleochroismis from reddish-yellow(lly) Bau,about 40 km SW of Kuching,Sarawak (Fig. I ), to brownish-red (llZ'). where limestone,shale, chert, sandstone.and con- glomeratebelonging to the Bau Seriesof Upper Ju- X-ray crystallography rassicto Cretaceousare exposed.They are locally The precessionand Weissenbergphotographic intruded by microdiorite,microtonalite, dacite, and studiesshowed the mineral to be monoclinicwith quartz-andesite of late Tertiaryage, and the volcanic possiblespace group either Cc or C2/c. The latter is activity is consideredto be responsiblefor the miner- preferredaccording to the resultsof a structuralanal- alization , of silver, , and mercury ysis (Nakai et al., 1977).The unit-cell parameters foundin the rocksof the BauSeries (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 samegeologic event. c = 16.87(l),4'and p : 117.58(4)". Only one specimen showing the mode of occur- In the sarabauitestructure (Nakai et al., 1977),the renceof sarabauitewas found. All descriptionsand studieswere made on this material. It is a pieceof gray fine-grainedlimestone cut by a sarabauite-bear- ing vein-likebody more than 5 cm in width. The modeofoccurrences ofsarabauite and the associated mineralsincluding stibnite, wollastonite, quartz, cal- cite,and minor senarmontiteare depicted in Figure2. Sarabauiteforms long tabular crystalselongated along the b axis, and the maximum lengthreaches I mm. A well-developedexternal shape was only occa- sionallyobserved under the oremicroscope; however, evenso, the morphologycould not be determined. The closeassociation of stibnite,senarmontite, and sarabauitesuggests the absenceof any stablephases with intermediatecompositions between CaSb,oO,o S.-SbrSB-SbrOsunder the conditions of sarabauite formation, which excludedthe formation of kerme- site. Physicaland optical properties Fig. 2. Sketchof the studiedsarabauite-bearing Sarabauitehas a realgar-like specimen.Sa: carmine-redcolor. sarabauite;Sb: stibnite(with minor senarmontite):Wo: wollasto- resinousluster, orangestreak, and no visible cleav- nite; Ct: calcite. NAKAI ET AL: SARABAUITE, A NEW MINERAL 717

Sb atomsare coordinated by threeO and/or S atoms this givesa certaindifference between the two struc- to form trigonalpyramids of SbO3,SbSg and SbSrO. tures.The kermesitestructure (Kup6ik' 1967)has a The SbOg pyramids compose4-membered and 8- similar network composedof Sb, S, and O atoms memberedSb-O rings.These two rings link by shar- parallelto (100).As mentionedabove, in sarabauite ing a cornerO atom to form a chainparallel to [001]. the netsare linked by the Ca atomsto form a three- On the other hand,two SbS3and two SbSrOpyra- dimensionalstructure, whereas in kermesitethe nets mids form an 8-memberedSb-S ring. Moreover the are stackedin the a axisdirection and linked by weak 8-memberedSb-O and Sb-S ringslink by sharinga Sb-S and Sb-O bonds.The averagebond distances cornerO atomto form a chainparallel to [101].As a are:Ca-O 2.467,9b-O2.000 and Sb-S 2.4654. Simi- whole, thoselinkages of ring structuresgive rise to a lar valuesare observed in kermesiteas well asin other two-dimensionalnetwork parallelto (010).The Ca oxidesand sulfides. atom is sandwichedbetween the two 8-membered The X-ray powderpattern obtained by the diffrac- Sb-O ringsand formsa CaOepolyhedron. Thus the tometer method using Ni-filtered Cu radiation is Ca atomslink the networksin the b-axisdirection. givenin Tablel. The indexingwas made on thebasis Kermesite(SbrSrO) is the only mineralwhich is of single-crystaldata. There is good agreementbe- compositionallyrelated to sarabauite.However, ker- tween intensitiesof the X-ray powder and single- mesitecontains no cationother than antimony,and crvstaldata.

Table l. X-ray powder diffraction data for sarabauite*

d obs l/lo hkl d calc d obs Ll Lo d calc 15 200 II.24 1r.33 20 10.0.2 r.922 r.922 r.890 22 202 8.224 6.4t0 6 825 1.888 1II 4.970 4.979 o I0.2.3 1.888 1,859 L.872 18b 5La 4 .452 4.462 36 026 602 4.227 42 623 r.859 II3 3.915 3.924 30 804 1. 859 15b 5L2 3.751 3.748 15 lI8 l. 834 r.830 600 3.748 oz I L .6Z0 7 004 3.738 L32 1.80s 1. 808 rJ . r. o I.79]- T.79L t2 JLZ 3.45r J. {OO 78 r.783 13 314 3.379 3.385 10 r33 1.780 5r4 3 -207 3.215 100 lro r. /lo r.756 TD 5tr 3.L79 3.L82 60 3L7 1.751 8 802 3.155 3. r64 50 oz+ 1.730 1.731 I8 712 3.0s0 3.052 6 531 L.692 L .694 L.673 ID 7].3 J.UU / 3.OII 5 12.2.5 r.o/l 1.672 I LL 2.970 2.970 5 732 020 2.827 2.8L7 88 823 r.o/r 2.816 733 r.655 r.ooo f, )La 2 406 2.8rf 734 1.538 1.640 8 800 2. 81r 10.0.4 L.623 L.620 9 22r 2.752 2-753 zv 5. 1. t0 r.501 1.503 t. )6u 8b zuo 2.7L3 z. tL6 z6 318 r.578 r.)/6 tL) 2.639 2.544 9 1. 571 5b 404 2 .606 2 .607 t8 , f o L.5TZ 2.580 2.583 40 l( I 7 1.569 11 r0.0. 4 2.507 2.503 I4 L>.L.2 1.559 1.550 2.498 15 935 a.)zo I.524 ID 006 2.492 IL / ro 2 .40L 2.409 LU.2-9 I.5L2 1.515 1.483 r.483 I 9r5 2.50L 2 .365 9 13.1. t0 o a't ) 2.327 2.329 5 f,ld L.448 1.450 910 2.285 2.28L 20 I.+5J L .432 J 10.0.0 2.249 2.251 5 04r r.407 L. 407 5D 4b 604 2.188 2.r87 4b* * 44L r.379 1.379 7r7 2-L70 4b L.377 9 6Za Z.LUO 2. r08 16 1.34r L.342 vz) 2.054 2.058 29 542 1. 340 1.328 2 fi. r. r 2.02r 2.023 D 7L8 r .326 r. 310 5 II.I.O 2,001 2.004 5 f3.r. r r.308 820 1.993 1 00( 5 2.o.tz 1.306 q7? f, lro I L.976 5 irs r.269 r.270 f zzo r.957 r.950 t2 ta.2.7 L.252 r.250 4 fd. o.s r.947 L.Y>Z L3 F.n.s r.235 L.236

* Cu/Ni radiation, diffractotneter methodl, 0.5o min **b: broad 718 NAKAI ET AL: SARABAL]ITE, A NEW MINERAL

Table2. Electronmicroprobe chemical analysis of sarabauite

t. molecuLar mole number ideal quotient (basis Sb=10) number 3.

Ca 2.43 2 .46 0.0514 0.99 I 2.49 5D 74.89 ta.I I 0.6223 l0 o 10 75.62 9.61 9.72 0.6075 9.76 10 9.94 D II.91 12.05 0.3759 6.04 6 11.95 Total 98.84 100.00 r00.00

I. Sarabauite, Sarabau mine, Sarawak, Malaysia. 2. Sarabauite, normalized to I00t. ? Theoretical CaShoeoSe,

Chemicalcomposition and properties Thermalstudy The electronmicroprobe analysis using JXA-5A Thermal analyseswere performedwith a heating analysergave the resultsshown in Table 2. Wave- rate of 2.5"C/min. The DTA and TGA curvesare length scansdisclosed only Ca,Sb, O, andS in major characterizedby a strongexothermic peak at about amounts and other elementswere not found. The 420" with a weight loss and a weak one at about standards usedwere stibnite,kermesite, valentinite, 490"C. The corresponding peaks for synthetic and wollastonite.Measurements were made at 25 kV CaSb,oOroSuare found at 410" and 490oC,respec- for Ca, Sb, and S, and 15 kV for O. The result tively. X-ray powder study of the product after ther- calculated : on the basisof Sb l0 leadsto theempiri- mal treatmentat 490oCrevealed that it consistsof a formula cal Cao.rrSbroOr.ruS..on.From the measured mixture of cubic Sbros,Sb2O4, and CaSbzO..The specificgravity,Z:4. latter two compoundssurvive in the product at The mineraldecomposes readily in conc.HCI with 1000.c. evolutionof HrS andvery slowly in conc.NaOH and diluteHN03 solutions. Synthesis Stoichiometric CaSbroO,sS6was hydrothermally synthesizedfrom CaO:SbzS, : Sb2O, : I : 2: 3 mixture in both cold-sealstellite bombs and silica tubesat temperaturesfrom 230 to 560.C under pressures from 30 to 1500kg/cm". The reactionrate is so rapid that the formationrequires only one hour at 500"C and 1000kg/cm". Although it includessmall frac- tions of recrystallizedacicular Sb2S, and polygonal SbrO, (either cubic or orthorhombic)in someruns, the product,including single crystals up to 3 mm elongatedalong the b axis,consists of aggregatesof carmine-redtablets having the same appearance, habit, and luster as the natural mineral.A scanning electronmicrograph of the syntheticcrystal is given in Figure3. SyntheticCaSb,oOroSu is made up of at leasttwo morphologicallydifferent crystals, columnar and tab- ular. They are elongatedalong the D axis like the natural crystals,and the latter are characterizedby a well-developed{100} form.

Acknowledgments We wishto thank Mr. K. Hirata,T. Okumura,and y. Kondo of Fig. 3. Scanning electron micrograph of synthetic CaSb,oOroSu. ElectronOptics Division,Jrol Ltd., for invaluablehelp with the NAKAI ET AL: SARABAUITE,A NEW MINERAL 7t9

K. Nagashimaand N' Morimoto (1977)The electronmicroprobe analyses. We expressappreciation to Mr. K. Nakai, L, K. Koto, sarabauiteCaSbroOroSo, a new oxide sulfide Ogawaof Departmentof Mineral Industry,School of Scienceand crysial structure of (Japan),27 5-27 6' Engineering,Waseda University, Tokyo, for measurementof re' mineral. Chem.Lett. The geologyand mineralresources of the flectances.Thanks are alsodue to ProfessorS. Kanno of Depart- Wilford, G. E. (1955) West Sarawak,including the Bau Mining ment of Geoscience,The University of Tsukuba, for information Kuching-Lunduarea, Mem. 3. about the geologyin the vicinity of the Sarabaumine. District. Geol. Suru.Bomeo' References receiued,Febtuary 18,1977' accepted Kupbik, V. (1967) DiE Kristallstrukturdes Kermesits'SbrSrO' Manuscripl publication,February 9' 1978' Nalurwis senschaften, 54, | 14. for