AmericanMineralogist, Volume64, pages 369-375, 1979
Newdata on hungchaoite,the second world occurrence, Death Valley region, California
RtcHnRoC. Eno, Jluss F. McAlr-rsrER ANDG. DoNeln EsrnI-urN U.S. GeologicalSuruey Menlo Park, Califurnia 94025
Abstract
Hungchaoiteoccurs with ginorite,mcallisterite, sborgite, sassolite, nobleite, ulexite, and, wheregypsum and ulexiteare abundant,with kurnakovite.inderite. and mcallisteritein surficialmatrix as productsfrom weatheredcolemanite and priceiteveins in late Tertiary rocks. Hungchaoiteis triclinic,space group PT;a :8.811(1), b : 10.644(2),c : 7.888(l)A;a : 103"23(l)',0 : 108o35(l)', 97.09(l), unit-cellvolume 666.2(l)Aa;Z 2[MgO.4BrOs.9HrO].Euhedral, tabular {100} to equant,colorless, untwinned crystals, up to 0.5mm, showl7 forms.The strongest lines in theX-ray powder pattern are, in A: 6.71(100), 3.3s6(92), 5.36(85 ), 4.093(78), 4.079(64), and 7.I 4(59). Hungchaoiteisoptically(-):*:1.445(2),0=1.485(2),7:l.a9}Q)(Nalight);2Il": ( -66.. 15(4)";r u,distinct; Xlta: +28",2Lb = 437",Y4 c = Good{lll}and {lll}and imperfect{010} cleavages. Hardness 2Yz. G (meas)1.706(5), p (calc)1.705 g cm-s. Hungchaoiteis metastablewith respectto inderite and mcallisteritein solution. Dehy- dration data are given.
Introduction of DeathValley National Monument. The first local- ity is about 50 m southwestof the road in Twenty Hungchaoite,MgO.2BrO3.9H2O, was first de- Mule TeamCanyon, 2,140 m N25'W of U.S.mineral scribedby (1964a,b) Chu et al. from salinelacustrine monument40 on Monte Blanco(McAllister, 1970), sedimentsat an unspecified localityin Chinawhere it andis in thesoutheastern part of the Meridianclaim. reportedlyoccurs as fine-grained materialassociated The secondlocality is about 550m S30'E from the with ulexite,hydroboracite, and szaibelyitein gypsi- firstand is on the SouthMeridian claim. The third is feroussediments. It is identical in its chemicalcom- on the Hard Scrambleclaim (Erd et al., 1959,Fig. 1), positionand physicalproperties with the compound about l0 km southeastofthe first localityand 3 km MgO.2BzOr.9H2O, first synthesizedby Nikolaev N72oWof Ryan. and Chelishcheva( 1940). The hungchaoiteoccurs in a surficial sponge We presentdata here for the secondworld occur- formed by weatheringof fragmentalbasalt around renceof this mineraldiscovered by McAllister in the veinsof priceiteand colemanite.The basaltunit is in Death Valley region, (1970). California The larger lacustrinedeposits in the lower part of the Furnace sizeof the crystalsin the California occurrencehas Creek Formation that was assignedsomewhat in- enabledus to characterizemore completelythis min- conclusivelyto the earlyPliocene (Clarendonian) by eral and haspermitted the determinationof its crystal K. E. Lohman(in McAllister,1970, p. 6) on thebasis structure(Wan and Ghose,1977). of diatoms.The formation,which reaches a thickness of about 2,100m, extendsupward into clearlythe Occurrence(J.F.M.) middle Pliocene(Hemphillian), according to Loh- In the FurnaceCreek borate area hungchaoite has man. In a stratigraphicsequence measured (McAllis- beenfound at three placesin the northeasternfoot- ter, 1976)from the underlyingArtist Drive Forma- hillsof theBlack Mountains. The localities are on old tion acrossTwenty Mule Team Canyonsoutheast of patentedmining claims of the U.S. Borax& Chem- the Meridian localities,this basaltunit is about 300m ical Corporation,which are now within the boundarv abovethe baseof the FurnaceCreek Formation and 00/03-004x / 79 / 0304-0369$02.00 369 ERD ET AL.: HUNGCHAOITE
Hungchaoite on the Hard Scrambleclaim, in con- trast to the other localities, occurs in a surficial aggre- gate that containsmuch gypsum and ulexite,at veins of priceite and colemanite. It is closely associated with kurnakovite, inderite, and mcallisterite,and is within a few meters of an assemblagecontaining riv- adavite, mcallisterite, ulexite, gypsum, and con- spicuousquantities of thenardite and mirabilite. Eu- hedral crystalsof hungchaoite(specimen no. JFM69- 5-5G7) for this report are from the Hard Scramble Y I locality. Three other specimensfrom the same gfab sample show the following mineral relations. (l) Nodules of hungchaoitecoalesce on a gypsum-kur- Fig. l. Tabular r,unl.nuoit. crystal in isometric p.B.rp".tiu", 1e; Standard orientation (with axial cross); (B) Viewed along Y nakovite intergrowth on corroded vein colemanite. Computer drawing by K. L. Keester using the computer program The oppositeside of the colemaniteis encrustedwith of Keesterand Giddings (1971). finer grained inderite and ulexite. (2) An irregular veinlet of hungchaoite penetrates an aggregate of about 100m abovethe colemanite-ulexite-probertite gypsum and weatheredbasalt on a core of coleman- ore zone. ite. Fine-grained inderite was depositedon a some- veinlet and Although the rocks enclosingthe priceite and co- what corroded surfaceofthe hungchaoite gyp- lemanite veins are of late Tertiary age, the hung- as nodules next to nodules of hungchaoiteon chaoite and associatedminerals around the veins are sum. (3) Ulexite, inderite, and hungchaoite occur Holocene and still form in the presentdesert environ- separately in nodules or crusts on an aggregate of grained ment, as shown by the fragile, ephemeralnature of gypsum and kurnakovite. Clots of very fine at- puffed ground in which the hungchaoiteoccurs and mcallisteriteare in a matrix of weatheredbasalt by encrustationsof some of the minerals on man- tached to the aggregate. made surfacesin prospectand mine workings (Erd et al.,196l,p.562; McAllister,1961, p.8300). Boron of CrystallograPhY the hungchaoite,which was releasedfrom weathered Morphology priceite and colemanite, apparently migrated much earlier from bedded ulexite in the ore zone. Hungchaoiteoccurs as euhedral to anhedral,tabu- Hungchaoite on the Meridian claim was collected lar {100}to equant,untwinned crystals (Fig. l) up to (specimenJFM58-l-8C) from a small pad of puffed 0.5mm in largestdimension. The formsobserved are ground that was not in contact with any of the ex- listedin Tablel. A numericaldescription of thehabit posed veins of colemaniteor priceite. Anhedral and developmentis providedby column D of Table l, subhedral hungchaoite or exceedingly fine textured whichlists the normaldistance of the form from the ulexiteforms commonly l- to 2-mm clots in a porous, origin.These data were obtained by Dr. KennethL. scarcelycoherent aggregateof montmorillonite and Keesterusing a computerprogram (Keester and Gid- residualanalcime. Gowerite. nobleite.and mcallister- dings,197 l) which exactlysimulates the realcrystal ite are very minor constituents. On the South (Fig. I ) andthus allows quantitative determination of Meridian claim, hungchaoiteoccurs with more abun- relativegrowth velocities.Although D valueswere dant boron minerals(although very minor ulexite),in not determinedfor six forms(Table l), they are all puffed ground of clay and analcime, down a moder- smallerthan k {011}and haveD valuesin excessof ate slope 1.7 m from the nearestexposed colemanite 1.400.The crystalmorphology indicates that hung- vein. The closelyassociated minerals in irregularclots chaoiteis triclinicpinacoidal. Furthermore, both nat- or nodules,generally less than 5 mm in diameter,are ural etchpits and thoseproduced by attackof cold ginorite, mcallisterite, sborgite, sassolite,nobleite, water show paired facesin accordwith centricsym- and ulexite. Other borate minerals thus far identified metry. from gowerite, the South Meridian locality are ward- X-ray data smithite, and aristarainite. The aristarainite is the second known occurrence (McAllister, 1976) after Unit-cell dimensionswere determinedfrom pre- Salta, Argentina (Hurlbut and Erd, 1974). cessionphotographs (Mo radiation,Zr filter) of ERD ET AL.: HUNGCHAOITE 371
Table l. Angle table and morphological data for hungchaoite
Triclinic; pinacoidal I
a:b:c=0.8278:l:0.7411 o= 103.23t, B= 108.35', y=97.09'
PotQo,to=0.8778:0.7079:1 ^=73" l5', p = 68'54r,r=77" 3Sl
pof 0.9672, qo,= 0.7800, xo,= 0.3362, yo,= 0.3179
D* *
Tabular Equant
001 46" 361 )Ao 501 68' 54' 73" l4l l . 000 0. 800 b 010 0" 00' 90' 00r 77" 35' 73" r4l 0.800 0.800 1 100 77" 351 90' 00 77" 351 68" 54' 0.125 0.125 f 410 89' l3' 90' 00t l1' 38' 89' l3' 72" 001 0.765 0.765 ' n 2ro 100" 55 90" 001 23" 201 100' 55' 75" 491 0.525 0.525 M rl0 t2l" l2l 90" 001 43" 361 I2I" 12' 83' 36' 0.4s0 0.450
| k 011 77" 021 48" 57 68" r5 ' 43" 521 29" 221 ]. 400 q 011 143' 58' 29" 4Sl 78" 321 ll3'59' 40" 251 not determined ' v 10r 67" 4Ll 54' l0 37" 00' 72" 041 31' 54' not deternined l0l -79" 451 37" 441 119' 02, 840 38' 50" ' 08, 0.97s 0.800 r l1 l0l" l4 52" 33'l 43" 20,, 98" 54' 41" 5l ' 0 . 950 0. 750 -63" z 414 221 34" 741 ll5'55' 75" 24' 47" 58' not deternined -50" x 212 35' 38" 13' tI2" 29' 66" 52' 47" 07 | not determined -34" u lll 271 47" 091 105" 54' s2" 45' 48" 16' 7.230 1.050 -13' S 131 57' 68" 23' 97" 261 25" 321 580 l5r not deternined p -737" 111 461 42" 091 723" tll 179" 47 | 66' 55' 0.975 0.975 -157' ' L2l 14 57" 331 l19" 05' 141" 05' 80" 37' not deternined
*Values calculated from unit-cell paraneters showr in Table 2. **Distance from the origin. Determination by K. L, Keester
singlecrystals from the Hard Scrambleclaim (speci- thesedata is 2.242g cffi-3,which is unlikelyfor a men no. JFM69-5-5G7).These data were refined by dimorph of hungchaoiteof specificgravity 1.703(5) least-squaresanalysis of the X-ray powder data and (Table2). Furthermore,Wan and Ghose(1977, p. areshown in Table2 comparedwith thoseobtained ll4l) have ques(ionedthe validity of the crystal from the syntheticcompound, MgO.2BrOs.9HrO. structureproposed for this phaseby Abdullaev and The crystalstructure of hungchaoitehas beendeter- Mamedovon the basisof ". . .a numberof impos- minedby Wan and Ghose(1977) using our crystals sibly short (<2A) oxygen-oxygencontacts. . ." On from the Hard Scramble occurrence.They show the other hand, Eyubovaet al. (1967)give X-ray hungchaoiteto be Mg[B,O'(OH)n].7HrO.Tung powder diffraction data for synthetic MgO. (1974) calculateda triclinicunit cell basedon the X- 2B2Os.9HrOthat do not agree with ours for the powder ray datafor the syntheticcompound given by synthetictriclinic compoundnor with rhed(hkl) cal- Chu et al. (1964b).Unfortunately, lines at 8.68 and culatedfrom the monoclinicunit cell of Abdullaev 7.95A,indexed by Tung as (100)and (010)respec- and Mamedov. X-ray powder diffraction data for tively,are not dueto hungchaoiteand haveled to an natural and synthetichungchaoite are given in Ta- incorrect unit cell. The density calculatedfrom ble 3. Tung'scell, with Z : l, is 1.599g cm-s. The syntheticcompound, MgO.2BrOr.9HrO, may Physicalproperties be dimorphous.According to Abdullaevand Mame- Hungchaoiteis brittle with good to perfect{Tl l}, dov (1969)the syntheticcompound is monoclinic; good {lll}, and imperfect{010} cleavages. Specific spacegroupP2r/a;a: ll.7l,b : 13.08,c:6.84A,B gravitiesof 1.706(5)(mineral) and 1.703(5)(synthetic : :4. l05o;Z However,the densitycalculated from compound)were obtained by suspensionin bromo- 3',t2 ERD ET AL.: HUNGCHAOITE
T able 2. Crystallographic data for hungchaoite explain the incorrect axiality reported by Nikolaev (1947)for the identicalsynthetic compound. Death VaIIey* Synthet ic* * The relativelylarge variationgiven for the ob- served2V (Table4) is dueto the difficultyin judging Systen Tric I in ic Triclinic the exact position of the diffuse melatopeseven Space croup PI P1 though both lay closeto X andwere easily reachable a (A) 8.8rr(r)i 8.800(r ) i the b 10.644 (2) r0 .648(21 by meansof the universalstage. Nevertheless, c 7.888(r) 7.89s (2) measured2V is really significantlylower than calcu- q l03' 23(1)' 103"23(1) ' B r08" 3s(1)' i08" 34(1)' lated valuesfor this angle using either our data or ' ' Y^ 97" 09[1) 97" 08(r) thoseof Chu el al. 0964b\. The limitationsof such V (A3) 666.2 (r) 666.3(r) a:b: c 0.828:1:0.741 O.826iIi0.742 calculationshave beenstressed clearly by Willard z 2 2 .. t' (le6I ). c (neas) t.zoo(s)t'- t .zos (s) p (calc) 1.703gcn-3 t./uJ gcm' Synthesisand stabilityof hungchaoitein solution *SpecimenNo. JFMs8-1-8C. The compoundMgO.2B2Os.9HzO was first syn- **Material synthesized by Dr. w. T. Schaller. tData obtained fron refinenent of X-ray powder data thesizedby Nikolaevand Chelishcheva in 1940.Their (Table 3) using the least-squares program of Applenan namefor thissalt, "magnesium diborate," is followed and Evans (1973). Enor in parentheses is one standard deviation. in the Russianand Chinesenomenclature. Synthetic itDeternined in bronoforn-acetone mixture checked with a encounteredin studies Westphal balance. hungchaoitewas subsequently of the MgO-B2Og-H2Osystem by Kurnakova(1947), Nikolaev (1947),D'Ans and Behrendt(1957), and form-acetone.The hardnessis 21/2.The mineraland Rza-Zadeet al. (1964).Our syntheticmaterial was syntheticcompound are colorless,have a vitreous preparedby the lateDr. WaldemarT. Schaller(oral luster,and arenonfluorescent. communication,1957), but the detailsof its synthesis areunknown. He mayhave been the first to recognize Opticalproperties (G.D.E.) the triclinicnature of synthetichungchaoite, for he The optical propertiesof hungchaoitefrom the reportedthat the material showed inclined extinction, Death Valleyregion are listedin Table4 and com- wasbiaxial negative, and hada verysmall 2V.D'Ans paredwith thosereported by previousworkers. In- and Behrendt'scomprehensive study of thesolubility dicesof refractionwere determinedin sodium light isothermsof the MgO-B2O3-H2Osystem at 25o,35o, by the immersionmethod in phasecontrast (Zernike) and 83'C showedthat hungchaoiteis formedonly as using a spindlestage similar to that describedby a metastablephase, in solutionsat temperaturesless Wilcox (1959).Refractive indices of the immersion than 35oC.This is confirmedby otherstudies of the mediawere checked with an Abbe refractometerus- systemat temperaturesranging from 45o to 200oC ing sodiumlight. (Rza-Zadeet al., 1966,and others). Stable phases The meanindex of refractionof hungchaoitecalcu- found in the systemat25"C are sassolite(orthoboric latedby the Gladstoneand Dale law from the ideal acid), inderite,kurnakovite, and mcallisterite.Rza- composition, MgO.2BrOs.9HrO, and calculated Zade et al. (1964)noted that hungchaoitebehaves as density(1.703 g cm-s)is 1.468.The measuredmean a metastablephase with respectto inderiteand mcal- refractiveindex (aBy) is 1.473. listeriteand is eventuallyconverted to one of these Figure2 illustratesthe relationsbetween principal phasesafter prolongedperiods at normal temper- opticaland observedcrystallographic elements. Data ature(less than 35oC)and pressureconditions. Ab- for the projectionwere obtained by meansof a uni- dullaevand Mamedov (1966)have offeredan ex- versalstage equipped with a Waldmannhollow-glass planationof the metastabilityof MgO'2B2Os.gHzO sphere.Single crystals, previously oriented by optical and its conversionto inderitein termsof the crystal goniometryand X-ray precessionprocedures, were structure model that they proposedfor this com- mountedwithin the spherein an immersionliquid of pound. However,as noted above,this structureis ND(25'C): 1.485,the B indexof the mineral.From probably in error. Wan and Ghose (1977) have the projectionit is evidentthat the Z vibration direc- pointedout that while molecularcomplexes of neu- tion is almostcoincident with [0ll]. Also, fragments tral chargeinvolving a boratepolyanion and a hy- lyingon the bestcleavage, {l I l}, givean off-centered dratedmetal cation are relativelyrare, they are pres- negativeBxa interferencefigure which might be inter- entin hungchaoite,inderite, and mcallisterite. We did pretedas uniaxialbecause of the small2V.Thismay not attempt to determinethe time necessaryfor the Table 3. X-ray powder diffraction data for hungchaoite 5t5
Ca1cul ated* 0bserved
Synthetic* * Death Valley*** Ch1naf,
([) ([) d'.tt (A) d',rZ (A) hkz Lrz !ir1a I ! I 010 10.I I6 I0. I 5 I0.1 4 --- 100 8.L47 8.13 16 8.15 8 8.01 l0 110 7.t39 ?.L3 52 7.I4 59 7.r8 60 011 6.853 6.85 10 101 6.709 6.71 59 6.77 i00 o.o/ 70 Ill 5.847 5 .84 36 5.85 58 5.84 60
111 5.367 5.36 38 5.36 85 5. 34 60 01I 5.186 5.18 2 5.18 6 020 5.058 5. 06 26 5.05 35 5. 05 40 120 4.782 4.786 24 4.787 24 4. 80 40 101 4.620 4.620 8 4.619 6 4.47 30 20r 4.260 4.255 q
721 4.232 4.235 6 4.233 8 4.25 10 210 4. 096 4 .093 100 4.093 78 721 4.096 200 4.074 4.077 95 4.079 64 4.O7 I00 72t 3.870 3. 865 27 J-do/ 36 3.86 50 lII 3.785 3.786 8 3.790 8
ot2 3.733 3.7s2 2 o27 3.665 3.666 19 3.666 31 3.66 002 3.583 5.586 3 220 3.569 3.574 7 3.574 10 05I 3.459 3.459 8 3.456 18 3.46 l0 t12 3.357 5.354 53 3.356 92 3.34 90 202 3.355
2t2 3.277 3.277 13 3.277 20 277 3.231 3.230 3 3.23r 4 3.20 272 3.099 3.098 3.100 t2 207 3.095 L2 221 5.061 3.06i 5 3.062 5 t2L 2.984 2.986 4 2.982 5
301 2.9t0 2.916 l0 o32 2.9C9 2.911 70 2.9t2 2.902 I00 131 2.907 311 2.885 220 2.884 2.885 10 t22 2.787 2.782 14 2.783 t2
310 2.776 2.775 l5 211 2.747 2.747 42 2.74E 37 2.734 90 2.777 15 2.7t7 l8 2.641 ( 2.647 o 2.577 24 32 2.569 70 2.517 l6 2.576 36 2.510 70
2.497 o 2.447 3 2.446 5 2.4r9 6 2.4t9 5 2.407 6 2.408 o 2.405 2.399 6 2.400 6 2.333 8
2.326 8 2.325 1l 2.306 1p 2.304 l4 2.304 2.289 7 2.283 9 2.256 6 2.256 6 2.228 ? 2.228 74 2.229 10
Plus additional lines all with: I < 23 r<28 I<60
*A11 lines are indexed to%W < 2.740'A. Indices fron least-squares anatysis of X-ray powder data using the digital computer progran of Appleman and Evans (1973) **lqatcrial s)nthesized by Dr..W. T. Schal1er. X-ray diffractometer conditions are: Chart No. X3507; Cu/Ni radiation, ).CuKql = 1.540514; silicon used as internal standaTd; scanned at ra" per ninute fron 8-88" 20. *"*Specinen No. JFM58-l-8C. X-ray diffractoneter conditions are: Chart No. X3508; Cu/Ni radiation; trCuKqr = I.54041A; silicon used as internal standard; scanned; scanned at 14" pet ninute from 8-108" 20.
#Data of Chu et aL. (f964b); Zhen Pei-zu, analyst. Intensities have been conyerted to base 100 for conparison. ERD ET AL.: HUNGCHAOITE
contrast,Chu el al. (1964b)show a lossof 20 weight percent(about 8 molesof HrO) by 90-100'Cand a lossof 40 weightpercent (about l5 molesof HrO) by 180'C.The dataof Eyubovaet al. (1967)accord with thoseof Chu et al. The dehydrationcurves shown by D'Ans and Behrendtand by Chu er al. aresimilar in shapebut differ in slope,a disparitythat may be due to differentrates of heating. We restudiedthe dehydrationof synthetichung- chaoiteusing 2 g of the materialprepared by Dr.
(0il I Schaller.The material was heatedwith an infrared I I lamp to 100'C and kept at this temperaturefor 24 --kI hours.A lossof 34.00weight percent (corresponding to l3 molesof HrO) occurredby 6 hours,but there was no further weight loss at this temperature.The compositionat this point was 2MgO.4BrOs.5H2O, in agreementwith D'Ans and Behrendt,but the ma- terial had becomean X-ray amorphousglass with n : 1.496(2).The samplewas then heated further in Fig. 2. Stereographic projection showing crystallographic elements and optical orientation of hungchaoite from the Death an electricfurnace to 700oC.There was a gradualloss Valley region, California. of waterup to 600oC,at whichpoint all of the water had beendriven off. The weight loss was 47.50per- cent,corresponding to l8 molesof HzO (47.45per- conversionof hungchaoiteto thestable phases. How- cent for the calculatedcomposition). The material everin one experiment,a crystalof hungchaoitesus- was still amorphousto X-rays at this point. At pendedover waterin a closedvial at 25"C remained 630(5)"Cit recrystallizedto form MgBaOT.The X-ray unchangedafter two months exceptfor the develop- powder data for the MgBoOTare in excellentagree- ment of etch pits on the crystalfaces. The crystalwas ment with thoseof Kuzel (1964),who first synthe- entirelyenclosed by a drop of solutionduring this sizedthis compoundin his studyof the MgO-BrO, time.Hungchaoite is slowlysoluble in coldwater and system.He pointedout that thereis no indicationfor the of the compoundMgBrOo in this sys- easilysoluble in cold dilute acids.Quantitative solu- existence bility data for the syntheticcompound are given by tem. We foundthat no furtherloss in weightoccurs D'Ans and Behrendt(1957). up to the melting point (985"C; Kuzel, 196zl)of MgBnOT. Thermaldata and stabilityof hungchaoitein air The DTA curvesshown by the variousauthors are Thermogravimetricand/ or differentialthermal an- Table 4. Optical properties alyticaldata for syntheticMgO.2BrOr.gHsO have of hungchaoite beengiven by severalauthors including Kurnakova (1947),Nikolaev (1947), D'Ans andBehrendt (1957), Death Valley Synthetic Eyubovaet al. (1967),and Chu et al. (1964b);the last o 7.44s(2)* 1.4415**L.442** authors also give correspondingdata for natural B r .48s(2) 1.4851 r.485 Y r.490(2) 1.4898 1.490 hungchaoite.The dehydrationdata are somewhat 2Ya 1s(2)'(obs) 36' (calc) 36o (calc) conflicting.For the following discussionit is 0rietation X,La=+28"1 conve- Zhb=+37" nientto considerthe unit-cellcontent ofthe synthetic \lrc=-66" Di spersion < ,, distinct compoundas 2MgO.4BrOs.l8HrO. D'Ans andBeh- " rendt(1957) postulated 2MgO.4BrOs.l7HrO for the unit-cell content.They found that 12 molesof HrO *Crystals from Hard Scramble clain; specinen no, JFM69-5- 5-G7. Deternined at 25'C in Na light. Error in paren- aregiven up on heatingto l00oC,forming the com- theses is one stmdard deviation. pound 2MgO.4BrOs. (the 5H2O compositionof syn- txData fron Chwet aL. (f964b). thetic halurgite).With further heatingthe structure fArgl" i, given as positive if it is neasured in the acute collapses;water is driven off gradually;and, above angle betueen the crystallographic axes of reference and 600oC,MgBrOn is formed after a loss of BrOs.By negative if it is neasured in the obtuse angle. ERD ET AL,, HUNGCHAOITE 375 in fairly good accord and may be explained on the and A. C. Vlisidis (1961) Nobleite, another new basisof our dehydrationstudy. There is a largeendo- hydrous calcium borate from the Death Valley region, Califor- nia. Am Mineral..46. 560-571. thermal peak at 95-105"C (Chu el al., 1964b,found Eyubova, N. A., L. G. Berg and P. F. Rza-Zade (1967) Thermal 170-180'C) correspondingto the loss of 13 moles of decomposition of magnesium borates. Dokl. Akad. Nauk Azerb. HrO; a smallerendothermal peak at 944-l040oC cor- ssR. 2.1.24-30. responds to the melting of MgBnOT.A medium to Hurlbut,C. S., Jr. and R C. Erd (1974)Aristarainite, large exothermic peak at 630-675"C reflects the re- Na,O.MgO.6810, l0HrO, a new mineral from Salta, Argen- Lina.Am. Mineral.. 59. 647-651. crystallization of the amorphous dehydration prod- Keester,K. L. and G. M. Giddings (1971)Morphological crystal- uct to MgBoOr. Nikolaev (1947) and Eyubova et al. lography via IBM 2250 interactive graphic display terminal (1967) also show a small endothermic effect at 375- (abstr.). Am. Crystallogr. Assoc. Summer Mtg., Iowa State 380'C that is not recordedby Chu et al. (1964b) and Unio., I97l , p. 45. for which we have no explanation. Kurnakova, A. G. (1947) Physicochemicalstudy of calcium and magnesium borates. Izuest Sektora Fiz -Khim. Anal Inst. Ob- The alterationof hungchaoitein air proceedsquite , shchei i Neorg Khim, Akad. Nauk SSSR, 15, 125-143.Through differently, however, under natural conditions, as Chem. Abstr.44, 6755a (1950). processesother than simple dehydration are oper- Kuzel, H.-J. (1964) Zur Kenntnis des Systems MgO-BrO3: Syn- ative. The alteration of hungchaoitewill be described these und rdntgenographische Untersuchungen der Verbindung separatelyin a forthcoming paper. MgO.2BrOs. Neues Jahrb Mineral. Monatsh., 1964, 357-360. McAllister, J F. (1961)Sborgite in the Furnace Creek area,Cali- Acknowledgments fornia. U.S. Geol. Suru. Prof. Pap.,424-8,8299-8301. - (1970) Geology of the Furnace Creek borate area, Death Part of the work was done in cooperation with the California Valley, Inyo County, California. Calif. Diu. Mines Geol. Map Division of Mines and Geology. Permissionwas granted by the Sheet 14 U.S. Borax & Chemical Corporation to work on its mining prop- - (1976) Columnar sectionof the main part of the Furnace erty. We appreciate the help of our Survey colleaguesDrs Michael Creek Formation of Pliocene(Clarendonian and Hemphillian) Fleischer and George L. Soleimani for translation of Russian age, across Twenty Mule Team Canyon, Furnace Creek Borate papers,and Dr. E. C T. Chao for translationof Chinesepapers. area, Death Valley, California. U.,S.Geol. Suru Open-fileRept. The manuscript has benefited from suggestionsby Judith A. Kon- 76-26L nert and George E. Ericksen of the U. S. Geological Survey. We Nikolaev, A. V (1947) Physicochemicalstudy of native borates. are grateful for the help of Dr. Kenneth L. Keester in providing the Izdatel. Akad. Naak SSSR, Moscow-Leningrad. crystal drawing and computer data. We thank Drs. Che'ng Wan _ apd A. G. Chelishcheva(1940) The 25" isotherm of the and Subrata Ghose for furnishing us with a preliminary draft of systems:CaOf BzO.*HrO and MgO*BrOi+HrO. C. R. (Dokl.) their manuscript. Acad. Sci URSS,28, 127-130. (1964) References Rza-Zade, P. F., G. Bagirov and G. S. Sedel'nikov Metasta- bility of magnesium diborate in the ternary MgO-BzOr-HzO Abdullaev, G. K. and Kh. S. Mamedov (1966)Magnesium dibo- systemat 25o. Azerb Khim. Zh. 1964, 117-126.ThroughChem. rate as a metastable member Abstr, 62, 5939d(1965). of the system MgO-BrO3-HrO. "/. _, Struct Chem 7, 831. [transl. from Zh. Strukr. Khimii,7,896, R. A. Abduragimova,G. S. Sedel'nikovand A. O. Afuzova l 9661. (1966) Solubility isotherms of the MgO-B,O'-H,O system at - and - (1969)Crystal structureofmagnesium diborate 45o and 70". Issletl. Obl. Neorg. Fiz. Khim., Akad. Nauk Azerb. Mg[B.OI(OH).] .6H,O. Issled Obl. Neorg Fiz. Khim. Ikh Rol ,SSR, Inst. Neorg. Fiz. Khim., 1966, 69-76. Through Chem Khim. Prom , Mater. Nauch, Konf., 1967,28-32. Abstr 67, 26323r (1967). Appleman, D. E. and H T Evans, Jr. (1973) Job 9214:Indexing Tung, C.-H (1974) X-ray powder photographic indexing and cell and least squares refinement of powder diffraction data. Natl constant determination of hungchaoite. Ti Ch'iu Hua Hsueh, Tech. Inf. Seru , U S. Dept. Commerce, Springfield, Virginia, t974,204-212. DocumentPB-216 188. Wan, C. and S. Ghose (1977) Hungchaoite, Chu, l-Hua, H. T. Hsieh, T. C. Ch'ien and L. P. Liu (1964a) Mg(HzO)uB.Ou(OH)o.2HrO: a hydrogen-bonded molecular Preliminary report on the occurrence of a new magnesium bo- complex. Am. M ineral., 62, | 135-1143. rate-hungchaoite, MgO 2BrOs.9HrO, in China. Sci. Sinica, Wilcox, R. E. (1959)Use of the spindlestage for determinationof t 3, 525-527 principal indices of refraction of crystal fragments. Am. Min- _ nn6l _ (1964b) Hungchaoite_a new eral ,44, 1272-1293. hydrous magnesiumborate. Acta Geol.Sinica,44, 351-356. Willard, R J (1961) A re-examinationof some mathematical D'Ans, J. and K.-H. Behrendt (1957) Uber die Exis- refations in anisotropic substances. Am. Microscopical Soc. tenzbedingungeneiniger Magnesiumborate. Kali u. Steinsalz,2, Trans..80. l9l-203. t2t-t37. Erd, R. C., J F. McAllister and H. Almond (1959) Gowerite, a new hydrous calcium borate, from the Death Valley region, Manuscript. receiued, May 22, 1978; California.Am. Mineral , 44,9ll-919. acceptedfor publication, June 23, 1978.