Kernite from Tincalayu, Salta, Argentina

American Mineralogist, Volume 58, pages 308'313, 1973

Kernitefrom Tincalayu,Salta, Argentina

C. S. Hunrsut, Jn. D epartment ol Geological Sciences, Hansmd (Jniuersity, Cambridge, Massochusetts02138r, L. F. AnrsrAn^crN ObseraatorioNacional De Fisica Cosmica, San Miguel, Pcia. B. A., Argentina

AND R. C. Enu U.S. Geological Suroey, Menlo Park, Calilornia 940252

Abshact

The Tincalayu mine (Salta, Argentina) is essentially a monomineralic deposit of borax partly transformed to kernite with minor amounts of several rare borates. The deposit is interpreted as an old playa accumulation, buried, metamorphosed and deformed by folding and faulting. It is intercalated with clastic continental sediments of Pliocene or post-Pliocene age. The principal explored lens is more than 30 m thick and approximately 100 m in diameter. Kernite crystals are clear, transparent and well developed; many exceed 30 cm in length and l0 crn across; no terminal faces were observed. X-ray powder data are given with the orienta- - - -+ tion: c > a, p 2 9O'.The spacegroup is Ph/c; a 7.016 ! 0.001A, b 9.152 0.0024; - - c = 15.678 -{- 0.002A. p - 108"52.8' !. o.7'; cell volume 952.6 -r 0.2A3; Z 4. a:b:c 0.7666:l:1.7131. Cleavage:{100} and {00I} perfect, {TOZ} poor. Optically biaxial (-);a: 1.545,P-1.473,.y-1.488-F0.001(Nalight);2V-80",r)o(slight);XAc-70'30', Z - b.Density (calc) 1.905 + 0.001 g/cma, specificgravity (meas) 1.906 = 0.003. A chemical analysisby wet methods gives wt percent Na,O 23.1, B,O, 51'0, and H'O 26.1 (total 100.2). nte analysisshows endothermic peaks at 1'75"C (very strong), 561"C (strong) and 755"C (very strong), and exothermic peaks at 361'C (weak) and 604"C (strong).

Introduction Hombre Muerto. The approximatelatitude andlongi- The mine can be Kernite was discoveredin 1925 during a drilling tude are 25"2A5 and 67'001W. from Pocitos Station on program by the United States Borax Company in reached by motor vehicle Railway, 146 km to the Mojave Desert, California. Although it was re- the GeneralManuel Belgrano ferred to as rcnorite (Palmer, 1927) by the Com- the north. remain the only localities pany, it was named kern:ite after Kern County by Boron and Tincalayu has been positively identified. How- W. T. Schaller(1927,1930) in the first published where kernite has been reported from description. The locality, originally given as the ever, a doubtful occurrence the Donets Basin (Zaritskii, Kramer District, is today known as Boron, Cali- the Lower Permianof possibleoccurrence has been indicated fornia, the name of the town that developedafter 1965), and a pan (Hunt et al., 1966), p. mining began. in the Death Valley salt Boron was the only known kernite locality until B-49). Ahlfeld found the mineral in the borax mine at Occurrence Tincalayu, Argentina. Only a superficialdescription was reported (Ahlfeld and Angelelli, 1948), and The Tincalayu mine is essentiallya monomineralic this second occurrencehas gone largely unnoticed. deposit of borax partly transformedto kernite with Tincalayu is in the Province of Salta at the nortb- a very minor content of severalrare borates.The central part of the salt pan known as Salar del depositis interpretedas an old marsh accumulation, 1 buried, metamorphosedand deformedby folding and Mineralogical Contribution 49O, Harvard University. direction 'Publication authorized by the Director, U.S. Geological faulting along a predominantlynorth-south Survey. so as to be intercalatedin the folded Sijesformation. 308 KERNITE FROM ARGENTINA 309

The borax is concordantly intercalated with mem- bers of the Sijes Formation which is composed chiefly of clastic continental sediments deposited in a closed basin. The principal rocks of the formation are fine-grained sandstonesand claystonesvariously colored white, grey, yellow and pink. These are in- terbedded with tuffs, evaporites, limestones, and conglomerates(Catalano, 1964;Turner, 1964;Mues- sig and Allen, 1957). Catalano considered the sediments post-Pliocene,whereas Pratt (1961) dated them as Pleistocene or Recent, and Turner (1964) as Pliocene. Lens-like bodies of borax are apparently localized by structural control along the North-South axes of the anticlines. The principal known lens is more than 30 meters thick and approximately 100 meters in diameter. The borax rests directly on a thick layer Frc. 1. Optical orientation of kernite, with c ) a and of halite and is overlain by about 50 meters of brown B > 90'. to reddish-brown fine-grained claystones, siltstones, tuffs and sandstones.Near the upper contact of borax and sediments are several thin claystones horizons. by two parallel faults. This elevatedportion was One of these horizons carries nodules of ulexite, an- the first part of the depositto be discovered,and it other contains euhedral inyoite crystals, and a third led Muessigand Allen (1957) to describeit as a has crystals of kurnakovite 1= "inderite" of Meus- plugJike body. sig and Allen, 1957). At Boron, California,kernite is found in the lower During the intensive folding and faulting, the part of the deposit as a metamorphic alteration of sedimentary series was elevated above the playa borax (Christ and Garrels,1959; Barnard and Kist- and partially eroded; later it was covered in part lel1966; Bowserand Dickson,1966; Smith, 1968). by a thin flow of Holocene basalt. The folded Sijes At Tincalayuthe generalrelationship of the two min- Formation not only forms high ground at the mar- erals is similar. Kernite in an irregular body in gin of the present playa but rises as islands within placesmore than 10 metersthick, underliesthe main it. The elevation initiated the present cycle of erosion deposit of borax. In addition a veinlike mass of and of deposition of clastic and chemical sediments kernite about 30 centimeterswide which cuts the (halite and ulexite) in the present playa. upper borax probably was formed by fault action. During the tectonic deformation of the deposit, a The portion of the Tincalayudeposit that is mined tabular portion of the borax ore body was raised is composedof a fine-grainedcrystalline aggregate of borax. Occasionally,well-formed, transparent crys- Tenre 1. Unit-cell Data for Kernite tals of borax are found in cavities which range in size from a few centimetersto over 30 centimeters.

Tlncalayu, Salta Ross and Edwards clese (1966) Locally thin layers of clay and silt within the lenses Argentlna 1959, synthetlc unknown source reduce the BzOs content,which in pure borax is Systen and Monoc I 1n1c Monocllnlc Monocllnlc percent. Material space group PJc PzI/ c 4r/ c 36.5 wt percent, to as low as 20 Unlt C€]l with 28 percent or greater is sent to the dressing 7. 016+0.001| 7.422 7 , 0172+0.0006 b 9.152+4.O02 9 151+0.002 9.158210.0006 plant. r5.6z8io.oo2 15.67 6- r5.6z74To.oor5 r08.52:8'+o Z, ro 8'50,+5' 108.8516+0.0020 the borax and kernite are very i rE'r 952.6+0.2- 953'4t'- 953 4 Associatedwith z 4- lr small amountsof the rare borates rivadavite, ezcur- p ( calc,g,/cn 3) r.905+0.001 1.90q*rt 1.93 sp.gr. (neas) 1.9o6Fo.oo3 t .91 rite (Hurlbut and Aristarain,1967a,b), ameghinite, and macallisterite(Aristarain and Hurlbut, 1967a, .In1tla1 parameters fron x-ray slngle-crystal precesslon datai f1nal parmeters Llsied here fron least-squares reflnenent of x-pay powder b). There are alsominor amountsof compactulexite data (Table 2); morpholo8lcal neasurenent of B gtves t08o 53'+4'. r* Calculated 1n present lnvestlgatlon fron da!a of Ross and Edwtrds balls and euhedral kurnakovite crystals. Thin veins (1959) alrhouCh Ross and Edwards dldn't repo.t 1t tft Calculated by Claldl et aL. (f967) fron the data of Ross and of halite and secondarytincalconite are also present. 310 HURLBUT, ARISTARAIN, AND ERD

Morphology and Physical Properties Tesre 2, continued The kernite crystals at Tincalayu are large, but (A) no terminalfaces were observed; crystals 30 cm long dwL(fr) I d..- r and 10 centimetersacross are common.Very char- {2 338 0.7 222 2 34D {2.338 0,0 213 12 337 0.4 acteristic of the occurrenceare intergrowths of two 2$ 2 30B 3-2 2 12 296 03 3r 2 29C large crystalsgiving a twin-like appearance.Freshly 232 12 29\ 89 is 12 2b7 \2 broken kernite clear and transparentwith vitreous 2 266 12 265 15 luster, but on exposureto air it turns milky white 0ql T2 267 0q 313 12 2\8 11 on the surfaceand alongcleavage cracks. 3 01r 2 ?qb 6 12 2C7 06 12 246 2I

2 ?30 6 2.230 z6 LO 2 2r3 58 T,lrrr 2. X-ray Powder Diffraction Data for Kernite from o42 {2 r86 1.5 2 r82 lt fincalayu 7 t2 182 .l t2 r52 3t 204 a,2 12 r5r 00 hkL Observed * a,r ^!,r o+6i tl dhkL(fl) r d..-(A) { 2 140 0l 2 llto b i2 138 94 223 {2 138 a2 011 779 9 7 789 002 7.40 100 7.417 I00 0 2tll 2.495 B 2 09r 53 100 6.64 85 6 638 {2 082 0.9 102 6.00 t5 6,006 2 080 9 {2.oBo !9 012 5 762 0.0 0q3 {2 076 31 111 5 538 o-2 12.455 0l 110 537 5.3't \ 2.2 2 O52 5 t 2 051 r6 \\2 5.03 5.A2r 0,8 127 2 0r3 5 2 Al2 1.8 fll r.68 \.676 2 003 7 2 042 4: 020 4.le 4 576 1.95b rl

021 \.373 38 t 9r2 13 013 4.348 4.350 0.9 r 942 8 102 4 298 4.303 2,7 1.881 5 4.233 \.233 7.0 r 857 3 422 {3 895 2-2 r 831 4 rr2 3.895 {3.894 I 820 121 3.823 01 lo4 3 8oo 7 3 804 r20 3.768 03 004 3.745 23 3.708 I2.I 122 540 09 3 r 7\5 r.72r 1r4 10.4 10 I 706 121 3 -542 o6 1.683 2A2 3.478 0.1 r 659 0f4 3-437 6 3.\37 2.7 3.358 7 3.358

200 3 312 9 3.319 2,O 3.304 8.6 (1927 first the mineral as 21r 3.260 65 Schaller ) described 212 33 3 3 240 4.2 orthorhornbic with c parallel to the intersection of t22 3 -r32 3 135 \2.6 the two prominent cleavages.Later he recognizedthe 2ra 3,r2O 11.3 3 098 14 monoclinicsymmetry and reorientedthe crystal,mak- Za\ 3 00j Q.0 031 2,989 5 2.988 40 ing old c : new b, c ) a and B < 9Oo (Schaller, 2tr 2 882 {2.882 r72 024 {2.881 9rr 1930). Garrido (1932) reporting unit cell dimen- 0r5 12.822 0.q 032 2,823 7 12 82r 33 sionsfollowed the rule a ) c andB > 90". 22r 12.t7\ 3.2 A third orientationin which c > a and 6 ) 90owas 130 2.773 10 12.772 92 222 12 769 3,2 used by Minder (1935),and followed by Ross and 2.732 6 o5 12.7 2A 04 2.119 6 12.719 0.5 Edwards(1959), Giese (1966) and Cialdi et al. (1967),

224 2.681 2.687 38 in their respective studies of kernite structure. 2.678 2.673 3.8 I06 {2 609 78 Schaller's a vabte obtained from morphological 2.609 12.6a7 04 double the true value as used by all 12.577 0.4 measurementsis 2 573 10 12.57r 22 of these authors. Except when otherwise indicated, 8.5 presentpaper. 8 {2.5r1 the Minder orientation is used in this 2 5rr 12 509 00 006 2 472 27 2 472 17.0 The transformationformula from Garrido to Minder, r24 2 430 7 2 \29 38 i.e.,fromorientation,c ato c ) a (P > 90" in both) ,a6 12 387 06 I or5 2.387 10 {2 387 49 t2.380 0.7 is: 001/010/100. Most of the following physicalproperties of kernite rx-ray dlffractemotbr 4ondit ons arer .hart No. xl)2r; arlxi raolatlo , ICuXa = 1.54lBAt Al used as internal standard; scanned at I/4o 2a per from are in closeagreement with those of nlnute. Tincalayu rxtar d.. - ' 3.000i. Below thls value calculated hlZ listed only^lor kernite Boron as determinedby Schaller(1930) ooselVga iet-ecriois. AIl refl-criors fo- uhlch d, , . / 0004 hav from been indexed. 1 calcuLated from parmeters or cai'lt! * aL. (1967) and reported in Dana's System of Mineralogy KERNITE FROM ARGENTINA 311

(Palache,Berman and Frondel, l95l). The cleavages TesLB 3. Chemical Analysis* and Atomic Proportions of are {100} and {001} perfect,{i02} poor. As givenin Kernite from Tincalavu Dana's Systemfor orientation c ( a, the cleavages -vith tltt llelght percent Atmlc proportlona are respectively{001}, {100} and {2011, {100} FF.rl enl afFd tn I nn perfectand {001}less so. Na20 23.1 Na 2.0356 The Mohs hardnessis 2Vz, the specific gravity B 4,0000 (meas) 1.906 i 0.003; the calculateddensity, from Hro H 7.9\27 the compositionNazO.2B2Oz. 4HzO, Z = TOTAL I00.2 r00.00 4 and rur, rw a!o, travalq unaverslEy, anatysl. A sPecErocnentcar salySIa lndlcates: 51, AL, Ca, Ll, X (0.01 - 0.001) and ilgj Mn, Ba, Sri Fe, unit cell volume,952.6 t 0.02A3,is 1.905f 0.001 Cu (<0.00]) percent. g/cm'; calculatedusing the analysisof Table 3 the valueis l.9IO g/cm9. (1957), The opticalproperties are: ,a : 1.454;F = 1.473; as predicted by Christ and Clark and -t- y = 1.488all 0.001 (Na light);2V = 80", Christ and Garrels (1959). There are two chains biaxialnegative, r > o (slight); X A c ='70"30' per unit cell that run parallel to the D-axis.As andZ : b (Fig. 1). With orientationa ) c,X A c shown by Giese (1.966), the linkage betweenthe = 38'30' and"Z : b. boron-oxygen chains along the c-axis is through hydrogen bonding, and along the a-axis through X-Ray Data hydratedsodium ions. The bonding within the chains The unit cell dimensionsfor the Tincalayu kernite, themselvesis much stronger than the bonding be- as obtained from precessionphotographs (MoKa) tweenchains, and thus the perfect {10O} and {001} and refined from powder diffraction data (CuKa), cleavages and the fibrous nature of kernite are compareclosely with previouslydescribed specimens readily understoodon the basis of the crystal struc- (Table 1). The interplanarspacings for the powder ture. data were indexed (Table 2) using the automatic A differentialthermal analysisof Tincalayukernite computermethod of Evans et al. (1963). Intensities gave three endothermicand two exothermic peaks, were calculatedfrom the atomic parametersgiven by as representedin Figure 2. The peaksof endothermic Cialdi et al. (1967), usingthe computerprogram of reactionsare at 175"C (very strong,very broad), Borg and Smith (1969). Observedand calculated 561'C (strong,broad), 755"C (very strong,sharp). intensitiesare in reasonableaccord, consideringthe The exothermicpeaks arc at 36loC (weak, broad) and 604'C (strong,sharp). strong preferred orientation due to the perfect {001} and {100} cleavages.To avoid hydrationto tincal- The alteration of kernite from Tincalayu appears conite the sample was ground under methanol; no to proceedmore rapidly than that from Boron, Cali- lines of this material were found. Other powder data fornia. Fragments of kernite from Boron that have for kernite were given by Mclntosh and Matthews beenin the Harvard University Museumfor 25 years (1948), MuessigandAllen (1957), Cipriani(1958) are still essentiallytransparent, and have only a thin andBowser (1965). white coating. Material from Tincalayu stored under similar conditions has become partly chalky white Chemisfry and Structure in two years time. Pure fragmentsof a large kernite cleavagepiece were selectedfor chemical analysis.Atomic propor- Tesrp 4. Chemical Analyses of Kernite (Wt Percent) tions resultant from the wet chemical analysiscar-

ried out by Dr. Jun Ito, Harvard University, yield ?lncaIayu, Calculated Callfornla Salta, Argent lna 1b (Table 3) the empiricalformula: 1.02NazO.2BsOB lon .3.97H2O, which is very close to the ideal formula of NazO.2BzOg'4ItO. Table 4 summarizesseveral Na2O 22.55 22.63 22,66 22.62 22.7 23.r 22,68 known analysesof the mineral. 50.80 50.76 50.90 50,52 50.95 The crystal structure of kernite was determined H.o 26.55 26.50 27.07 26.37 26.6 26,r 26.37 almost simultaneouslyby Giese (1966, 1967) and 1) Schaller (1930), Br0! by difference. Cialdi et al. (1967), and its structuralformula deter- 2 ) Schaller (1927 ,L930) . 3) clprldl (1958). minedto 4) Laboratorlo Qulnlco de1 Instlluto de Ceolo8la y Mlnerla' JuJuy, be Na2BaO6(OH)2'3HrO.The crystalcon- Argentlna; Ahlfeld and Angelelfl (1948). 5) R. Herzenberg, analysti Ahlfeld and Angete]ll (1948). tains infinite chains of composition [BrOo(OH)r]r* 6) Thls study, Jun Itor analyst. 312 HURLBUT, ARISTARAIN, AND ERD

Ce.rlreNo, L. R. (1964) Estudio geol6gico econ6mico del Salar del Hombre Muerto (Puna de Atacama). Argent. Rep. Min. Econ., Dir. Nac. Geol. Min., Est. Geol. Min. Econ. Serie Argent. 4, l-131. Cnnrst, C. L., ewo J. R. Cum (1957) The nature of the polyions in some borate minerals (Abstr). Geol, Soc. Amer.Bull.68, 1708. (1959) among Kern ite eNo R. M. Gennns Relations sodium borate hydrates at the Kramer deposit, Boron, California. Amer. L Sci.257, 516-528. Crrrnl, G.,E.Coxrzze, lNo C. SesEur (1967) La struttura cristallina della kernite, NazB,ou'(oH)"'3H'o, Acad. Naz. Lincei, Ser. VIII, 42r 236-251, CrrnIewt, C. (1958) Ricerche sulla disidratazionedi alcuni borati naturale. Atti. Soc. Tescana .Sci. Nat. 55A' 284-322. EvlNs, H. T. Jn., D. E. AppnMAN, AND D. S. Hlnn' wERKER(1963) The least squaresrefinement of crystal unit cells with powder diffraction data by an automatic computer indexing method. Amer. Crystallogr. Ass., Abstr. Annu. Meeting, 1963, Cambridge,U.S.A. Grnnroo, J. (1932) Symmetrie und Raumgruppe des Ker- Frc. 2. Curve showing the differential thermal analysis of nites (Na,B.O"'4H"O). Z. Kristallogr. E2, 468-470. kernite; heating rate 20'C per minute, reference junction Grese, R. F., Jn. ( 1966) Crystal structure of kernite, 0"C; thermocouple PtlPt + 13 percent Rh, reference Na,B,O.(OH),'3H'O. Science, 154, 1453-1454. material Al,O,. (1967) The crystal structure of kernite, Na,B.Ou(OH),'3H,O (Abstr). Canadian Mineral, 9, p. 29O. Hur.rr, C. 8., T. W. RonrNsoN,W. A. Bowrps, eNo A. E' Acknowledgment WesnsunN (1966) Hydrologic Basin Death Valley, Cali- fornia, U.S. Geol. Suro. Prol. Pap.494-R. The authors wish to express their appreciation to Mrs. Hunrsur, C. S. Jn., ANDL. F. Antsteuru (1967a) Rivada- Judith A. Konnert of the U.S. Geological Survey for calcu- vite, NaoMgB*O*'22HA, a new borate from Argentina. lating the intensitiesof the diffraction maxima. Amer. Mineral, 52, 326-335. AND- (1967b) Ezcurrite,2Na*O.5BO,.7H,O: References A restudy. Amer. Mineral. 52' 1048-1059. MclNrosn, A. O., lNn F. W. Mermsws (1948) The hy- Anlrtto, F., lNo V. Axctrtrrr (1948) Las especiesmin- dratesof sodium tetraborate.Amer. Mineral.13r747-748' erales de la Repriblica Argentina. Unio. Nac. Tucumdn, MENZEL, H., eNn H. Scrrurz (1940) Zttt Kenntnis der Inst. Geol. Mineria, Jujuy, Pub. 45E, 162-168. Borsduren und borsauren Alkalisalze. X. Der Kernit An$renerN, L. F., rNo C. S. Hunrsur (1967a) Ameghinite, (Rasorit) Na"B.O''4HO. Z. anorg. allge. Chem. 245, Na"O'3B,O'4ttO, a new borate from Argentina. Amer. t57-220. Mineral. 52,935-945. MINDER,W. (1935) Uber den Bau einiger Hydrate von AND_ (1967b) Macallisterite, 2MgO.68,0,. Natriumdibor at. Z. Kristallogr. 92, 3Ol-3O9. 15H0, from Salta, Argentina. Amer. Mineral. 52, Mulssrc, S., AND R. D. Au-nN (1957) Ezcurrite r776-1784. (2Na,O'5B"Or'7H,O), a new sodium borate from Argen- and associated minerals' BenNlno, R. M., eno R. B. Krsrrsn (1966) Stratigraphic tina: Occurrence, mineralogy 52, 426437. and structural evolution of the Krama sodium borate Econ. Geol. Pe.recnr, C., H. BrnrvrAN,AND C. FnoNppr' (1951) The ore body, Boron, California. Northern Ohio Geol. Soc. Systatn of Mineralogy of Dana, 7th Ed., VoI. II' lohn 2nd. Symposiumon Salt,1, 133-150. Wiley and Sons,New York. Bonc, L Y., lNo D. K. Surtr (1969) Calculated x-ray PALMER,L. A. (1927) Kernite or rasorite' Eng. Mineral. l. powder patterns Geol. Soc. Amer. for silicate minerals. 123, 494. Mem. 122,896 pp. Pnlrr. W. P. (1961) Local evidence of Pleistocene to BowsER, C. I. (1965) Geochemisty and petology of the Recent orogeny in the Argentine Andes. GeoI. Soc. Amer. sodium borates in the' nonmarine eoaporite enuironment, BuII.72, 1539-1550. Ph.D. dissertation,University of California, Los Angeles, Ross, V., eNo J. O. EDWARDs(1959) On the crystal struc' 307 pp. ture of kernite Na,B.O''4ILO. Acta. Crystallogr. 12, .rNo F. W. DrcKsoN (1966) Chemical zonation of p, 258. the borates of Kramer. California. Northern Ohio Geol. Scnrrrsn, W. T. (1927) Kernite, a new dium borate' Soc., 2nd, Symposium on SaIt, l, 122-132, Amer. Mineral. 12, 24-25. KERNITE FROM ARGENTINA 313

(1930) Borate minerals from the Kramer District, Zentrsxn, P. V. (1965) Boron mineralization in the Arte- Mohave desert, California. U.,S. Geol. Suru. Prof. Pap. movka Foundation in the Bakhmuta depression of the 15E-L 135,173. Donets basin. Transl. from DokI. Acad. Sci', USSR' Sunn, W. C. (1968) Borax solution at Kramer, California- Earth Sci. Sect. 149. 157-I59. Econ. GeoI. 63, 877-883. TunNen, J. C. M. (1964) Decripci6n geol6gicade la Hoja 7c., Nevado de Cachi, Provincia de Salta. Min, Econ,, Mahuscript receioed,IuIy 10, 1972; acceptedfor publication' Dir. Nac. Geol. Min., Bol. 99, l-78. Nouember 3' 1972.