Canadian Mineralogist Yol.24, pp. 689-693(1986)

MINERALOGYOF HILGARDITE-4MFROM EVAPORITESIN NEW BRUNSWICK

ALAN L. RACHLIN ANDJOSEPH A. MANDARINO Departmentof Mineralogyand Geology,Royal OntarioMuseum, Toronto, OntorioMSS 2C6, and Departmentof Geologt, Universityof Toronto, Toronto, Ontafio MSS IAI

BERNARD L. MUROWCHICK InternationalMinerols and ChemicalsCorporation, Bartow, Florida 33830,U.S.A.

ROBERT A. RAMIK Departmentof Mineralogltand Geologlt,Royal OntarioMuseurn, Totonto, OntarioMsS 2C6

PETE J. DTINN Departmentof Mineral Sciencu,Smithsonian Institution, Woshington,D.C, 20560,U.S.A.

MALCOLM E. BACK Departmentof Mineralogltand Geology,Royal OntarioMweum, Toronto,.OntarioMSS 2C6, and Departmentof Geology,University of Toronto, Toronto, OntarioMSS IAI

ABSTRACT au Nouveau-Brunswick. C'est une esplce monocliniqqe, groupespatial ,4a, a 11.470(3),b ll.32l(4), c 6.321(5)A, P 9O.O2Q)".Elle estbiaxe positive, a 1.623Q)'P 1.628Q), = Hilgardite*4M occurs as euhedral crystals in the Salt t 1.656Q),2V34Q)"(mesurd),46" (calcul6)' Y b: ZItc Springs and Penobsquis evaporite deposits of New Brun- : 1' dans l'angle aigu €. Les densit6smesuree et calcul€e swick. It is monocligric,space group Aa, a 11.470(3),b sont2.67 (3) et 2.676Q), respectivemenl.Les cristaux de ces ll.32l(4), c 6.321(5)A, I : fr .U2Q)n . The mineralis biax- localitds sont plus complexesque cerD(de la localitd type ial (+), a 1.623Q).p r.628(2),t l.6s6Q\. 2V (meas.) en Louisiane; les formes suivantesont 6tdidentifides: {010}, 34Q)",2V(calc.)Mo,Y = b, Ztrc = l" (intheacuteanCle {r00}, {160},{l4Q}, {llq}, {01!}, {1il}, {341, {2rr\, 0). The measuredand calculated densitiesare 2.67(3) and 123U,_ls22l,l3r rl, {5221,{2311, 1322}, {t3r}, 1122}, 2.676Q) g/cm3, respectively.The crystals from New Brun- et 13221.Trois cristaux ont 6t6 analys6si la microsonde swick are more complex morphologically than the type 6lectronique; nul autre cation n'est pr€sentque le calcium, material from Louisiana, andthe following forms havebeen sauf un peu de shontrum. Certains cristaux en plaquettes, identified:{010}, {100}, {160}, {l_40}, {ll0}, {01U, {lll}, riches en Sr lle rapport Ca/(Ca + Sr) atteignant 0,55], ont {322},l2r rl, l23r),1s221, 13 r rl, ls22},1231\, 13221, aussi 6t6 analyses, mais ce mat6riau semble un polymor- { I 31 }, { 122} and {3?21.Electron-microprobe analyses of phe triclinique de la hilgardite4M. L'$chantrllon le plus thee crystals showed no cations other than Ca and minor riche en Ca a donn6: CaO 32.1, SrO 0.3, Cl 10.2' B2O3 Sr. SomeSr-rich, platy crystalswith valuesof Ca,/(Ca+ Sr) (52.4),IJ2O(5.4), somme 100.4, moins O = Cl 2.3,total as low as 0.55 were also analyzed,but this material appears 98.190(en poids). Le B2O3et l'eau sont calcul6spour se to be a triclinic polymorph of hilgardrte4M. The most Ca- conformer d la formule iddale Ca2B5OeCl.H2O'Une rich samplegave the following analytical datai CaO 32.1, analysethermogravimdtrique et de gaz d6gag6du mat6riau SrO 0.3, Cl 10.2,B2O3(52.4), H2O (5.4),[email protected], less du Nouveau-Brunswicka donnd 5.990d'eau et 17.AVode O=Cl 2.3, total 98.1 wt,qo (with B2O3and water calcu- HCI et autres composants volatils. Le matdriau de Loui- lated to conform to the ideal formula, Cap5OeCl.H2O), sianea donn€ desr€sultats trbs semblables.Le HCI seserait TGA and evolved gas analysis of New Bruisfoik ma6rial lib6r€ des canaux de cette structure zdolitique. gave 5.9 wt.qo water and 17,4 wt9o (FICI + other vola- Cfraduit par la R6daction) tiles). Very similar results were obtained from the Loui- siana material. The HCI probably is derived from the con- Mots-clts : hilgardite, hil eardtte4M, Nouveau-Brunswick, tents of channels in the zeolitic structure. nouvelle localit6, 6vaporites.

Keywords: htlgardite, hilgardite-4M, New Brunswick, new INTRODUCTIoN occutrence, evaporites. Minerals ef 1foehilgardite-tyretskite goup are rela- SoMMAIRE tively rare and have been recognized in only a few occurrences. Hilgardite was flrst described by Hurl- On trouve la hilgardite4Men cristaux idiomorphes dans but & Taylor (1937) from the Choctaw salt dome, lesgisements 6vaporitiques de Salt.Springset Penobsquis, Iberville Parish, Louisiana. Subsequently, parahil- 689 690 TI{E cANADIANMINERALOGIST gardite, a triclinic polymorph, was describedfrom The crystalsare colorlessto slightly reddish brown the samelocalily by Hurlbut (1938).Braitsch (1959) and have a white . The mineral is transparent, described a mineral which he referred to as stron- has a vitreous and is not discerniblyfluores- fiehilgardite or I Tc-strontiohilgardite from Germa- cent in either short-waveor long-waveultraviolet ny. Kondrat'eva (1964)determined the crystal struc- . radiation. The Mohs hardnessis 5. Hilgardite-4M ture of a triclinic polymorph of the hydroxyl hasa perfect cleavageon {010}, a good cleavageon analogue of hilgardite and named it tyretskite. A {100}, and a conchoidalfracture. The densityoffive mineral named Cl-tyretskite was described by different euhedralcrystals was measuredusing a Ber- Hodenberg & Kiihn (1977)from salt depositsin Ger- man balance and toluene with the appropriate many. Rumanova et ol. (1977) solved the crystal temperature-correction.The mean of thesedetermi- structure of an unnamed ,,triclinic hilgardite" from nationsis 2.67(3)g/cm3, which comparesfavorably the U.S.S.R. Hilgardite crystalswere identified by with the value 2.616Q) g/cm3 calculatedfrom the Murowchick (1978) during mineralogical examina- unit-cell parameters and the chemical composition tion of drill coresrecovered in the early stagesofthe according to the method outlined by Mandarino exploration and development of some New Brun- (l98lb). swick potash deposits. Crystal-structure determina- The indicesof refraction of a polishedsection of tions were carried out on hilgardite from Louisiana one of the euhedralcrystals were measuredon a gem by Ghose& Wan (1979)and on parahilgarditeby refractometeraccording to the method of Hurlbut Wan & Ghose(1983). The confusion surrounding the (1984). A filter was used to transmit light of nomenclature of the hilgardite-tyretskite group has wavelengthapproximately 589 nm. The value of 2Z beenclarified by Ghose(1985). His systemof nomen- and the orientation of the optical indicatrix were clature for tlese minerals was approvedby the Com- determinedby meansof a spindlestage using another mission on New Minerals and Mineral Names of the crystal. The optical properties of hilgardite-4Mfrom International Mineralogical Association. New Brunswick and Louisiana are compared in According to the Ghosenomenclature, the name Table l. of the mineral described in this paper is The mean value of K6, for the three analyzed hilgardite-4M. euhedral crystalsis 0.231, and the value of Kp is the compatibility of the meanindex OccuRRENCE 0.237.Therefore,

A number of mineralogically interesting borate 'I. potash TABLE OPTICALPROPERTIES, DENSITY AND COMPATIBILITY INDEX minerals occur in the depositsof southern OFHILGARDITE.4M New Brunswick.Roulston & Waugh(1981) described the generalgeology ofthe depositsand listedthe var- NewBrunswick Louislana (This study) (Hur'lbut E ious minerals found in each of them. Briefly, the Tiylor 1937) potashand salt dppositsare part of a thick sequence optical Propertles of Mississippianevaporites known as the Windsor Biaxial (+) Group. This sequenceoccurs in the Moncton sub- Refractive indlces 'r.623(2) 't.628(2J 1.630(2) basin, which is in the southwesternpart of the north- B 1.636(2) Y r.656(2) 1.6q4(2) easterly trending Fundy geosyncline.Two of the 2v (calc.) 460 ^ 50: 2V (reas.) 34(2')" 35" evaporite deposits, the Penobsquis and the Salt 0ri entationI Y.b Y"b Springs,consist of a basalanhydrite, a lower halite = Z:c " lo Z:c l.5o member, a sylvite ore zone, a middle halite mem- Di spersiqn: r > v, moderate r > v, moderate ber, an upper anhydrite unit and an upper halite Denslty (g/cmJ) measured 2.67(3) 2.71 member. The majority of the borate minerals are calculated 2.676(21 2.71 Compatibllity index -0.026 -0.022 found in the middle halite member.The boratesare (excellent) (excellent) readily separatedfrom the halite matrix by solution in water and include the following species:, colemanite,hilgardite-4M, hydroboracite,priceite, szaibelyite,veatchite and volkovskite. This occur- TASLE2. TABLEOF ANGLESFOR HILGARDITE-4M FROM NEII BRUI{SIIICK rence of volkovskite is presentlyunder investigation. foms phi rho foms

GENERAL APPSARANCS, PHYSICAL DATA AND 010 oooo' goooo' 231 33 21 63 29 Dare 100 90 00 90 00 522 67 56 56 04 OPucer 160 920 9000 31i 7t 20 -60 11 140 13 52 90 00 s22 67 56 -56 04 110 44 37 90 00 231 3320 -$A The hilgardite-4M examinedin this study occurs 011 00 02 29 l0 322 55 57 -44 55 as isolated, almost equant, euhedralcrystals up to 111 44 38 38 07 13I 18 12 -60 26 322 55 58 44 56 r22 26 L4 -31 54 4 mm in size.Groups of subparalleleuhedral crys- 2rt 63 08 5l 0l 3zz -55 58 -44 56 tals of a platy nature are much lesscommon. HILGARDITE.4M FROM NEW BRUNSWICK 69r

TABLE3. UNIT-CELLPAMMETERS OF HILSARDITE-4M A single-crystal precession study confirmed the spacegroup.4a given by Ghose& Wan (1979).The group: = Monoclinic, Space Aa, z 4 unit-cell parameters were refined from thp X-ray NewBrunsrick Loulsiana powder-diffraction from a Debye- (This study) (Ghose& fan 1979) data'obtained Scherrer film produced in an internally calibrated a rr.otol:1A rt.n:e121E camerawith a diameter of 114.6mm using CuKa b 11.321(4) 1r.3r8(2) X radiation. The unit-cell data obtained in this stitdy c 6.32i(5) 6.318(1) B 90.02(7)9. e0.06(1)o^. are comparedto those given by Ghose& Wan (1979) v 820.8(7)AJ 817,82(26)A" for material from Louisiana in Table 3. The X-ray powder-diffraction data do not differ significantly from thosegiven in the JCPDS Powder Diffraction File (Card ll-N4). TABLE4. CHEMICALANAI.YTICAL DATA FOR HILGARDITE-4M . CHEIVIICAL DATA NewBrunsxlck Loulsiana Theor. t2 3 4

Ca0 33.82 32.1 31.3 31.9 35.14 Electron-microprobe analyseswere carried out on Sr0 0.3 I.5 0.6 Bror 52.48 (52.4) (52,r ) (52.3) ;o'.i, cT- 10.69 10.2 10.2 10.3 10.59 H20 5.43 (5.4) (5.4) (5.4) 6,44 sum ro2.4r (100,4) (r00.5) (r00.5) r02.39 - 0=Cl 2.41 2,3 2.3 2.3 2.39 192 Total (e8.r) (e8.2) (98.2) 100.00 3

Notes: l. Analyses I through 3 are for euhedral crystals from A 4 NewBrunswick. 2. Analyses I and 2 are from the sane crystal O with 2 representing the highest Sr0 yalue fro the Sr-rlch areas. Q - This crystal has a boracite core. 3. Analrsls 4 is for J ti Louislanamaterial (HurlbutI Taylor 1937). 4. 8201and H20 contentsare calculated for the ldeal fomula in a-na-lvsesT through-3.-5..The-analy-tlcat data for analJsis.4 u-as-- 8 recalculated to 100g after subtractlna1.89 g insoluble res idue. of refraction, the calculateddensity and the chemi- cal compositionis -0.026, i.a, excellenton the scale proposedby Mandarino (1979,l98la). For the data given by Hurlbut & Taylor (1937)for crystalsfrom Louisiana, the values of l(6, and K, are, respec- lively,0.232 and0.243, so that the compatibility is -0.M3 or good. However, the density given by Hurl- but & Taylor (1937)was calculatedfor the old for- mula. Using the density calculatedfrom the formula and unit-cell parameters given by Ghose & Wan (1979),the value of Kp is 0.237, so that the com- patibility of the Louisiana hilgardite-4M is -0.022 or excellent.

CRYSTALLoGRAPHIC DATA 400 600 800 1000 Morphologically, the euhedralhilgardite4M crys- T ec) tals from New Brunswick are much more complex gas than those describedby Hurlbut & Taylor (1937). Fro. l. Thermogravimetric curves (a) and evolved (b, hilgardite-AM. a, Weight-loss curves A total of eighteenforms have beenidentified by an curves c) for ( New Brunswick,5.33 mg) and (...... Louisiana, opticalgoniometric They study. are: {010}, {100}, 10.63mg). b, c. Evolvedgascurves for New Brunswick {160},{140}, {ll0}, {0ll}, lrtr\, {3221,{21r\, (b) hilgardite4.M and Louisiana (c) hilgardite-4M. {2311,ls22), 1311), ls22l, 1231ll,{322\, {r31\, Or

TABTE5. TM/EOADATA FOR HILOARDIT€-4M ing from 5.55to 5.9 wt. Vo,peaked at approximately 530'C; the evolvedgas analysisshowed that it was 123 due to H2O. This loss is sliehtly higlrer than lhe loss Smple I'l€Jght(mg) 8,02 5.33 t0.630 Loss in vacuum(wtr X) <0.6 not 0.2 of H2O predicted (5.30 wt. 9o) from the ideal detectable formula. Tmperature Interval rl 350-6450C 300-6700C 380-6500c Peak 5320C app. 540oC 525.0c The secondloss, ranging from 16.8to l7 .7 wt. To, Loss (wt, g) Tenperature Interval f2 645-10900C 670-10900C 650-l2l50c is difficult to interpret. It peaked at approximately Peak 10600c t0750c 10500c of abundant Loss (wt. g) 17.4 t6.8 17.7 1060'C and is marked by tle evolution HCl. However, sinultaneous detection of a signifi- Notes: SmDles 1 and 2 are from NewBrunswlck. SilDle 3 is fron cant quantity of BCln molecular fragments, as well Loulsiana. as of CaCln and possibly BOn fragoents, indicated the evolution of additional volatile species. This preventeda quantitative determinationof the evolved three euhedral crystals. The analyseswere done with HCl. These results raise the question of the source an ARL-SEMQ electron microprobe ulilizing an of the excesshydrogen. Ghose& Wan (1979)showed operating voltage of 15 kY and a sample current of that the Louisiana hilgardite4M has a zeolite-t1pe 0,025 pA, measuredon brass. After checking for composed of an open three- homogeneitywith a small beam-spot,samples were dimensionalborate framework with large open chan- analyzed with a 60-pm beam spot. Wavelength- nels parallel to the o and g axes(the two channels dispersion scansindicated the absenceof other ele- havediameters of 6 and 5 A, respectively).The HCI mentswith atomic numbersgreater tJnn I l. The ana- may be derived from thesechannels, but the man- lytical data were obtained using the following stan- ner in which it is producedis, asyet, unknown. These dards: celestine(Sr), hornblende(Fe, Mg), NaCl (Cl), channelsprobably also account for tle slight excess synthetic wollastonite (Ca) and microcline (K), and of H2O over the theoretical amount. correctd{ using a modified version of the MAGIC-4 program. The analytical data are given in Table 4. AcKl.lowLEDCEI4EI.ITS The B2O3and H2O contents were calculated from the ideal formula. It can be seenthat the euhedral The authors are grateful to the late Mr. R. C. crystalshave composilionsclose to t}le ideal formula, Staveley, who was partly responsible for initiating Ca2B5OeCIeH2O,with little substitution s1 51 1s1 this sfudy. We thank Mr. B. D. Sturman, who kindly Ca. Someplaty material, on the other hand, shows measured the optic axial angle of one of the substantial substitution of Sr for Ca, with values of lnlgardrte4M crystals from New Brunswick. It is a the Cal(Ca+Sr) ratio ranging from 0.97 to 0.55. pleasureto dedicatethis paper to Prof. R. B. Fer- Electron-microproberesults suggest that this material gusonon the occasionof his retirement.The authors, is hilgardite4Mor one of its polym.orphs.An X-ray along with many other mineralogists, have benefit- powder-diffraction pattern of one of the crystalswith ted from his research. high Sr, removed from the section after electron- microprobe analysis,issimilar to that of the triclinic minsl'{ describedby Rumanova et ol. (1977) and REFERENcES probably is hilgardite-lZc Further study ofthis Sr- rich, platy material from New Brunswick is under Bnarrscu, o. (1959): l?c-Strontiohilgardite (Ca, way. Sr)rlBsOn(OH)zCIlund seine Stellung-Heidetb. in der nftle'ardite-eruppe"XttB5O6(OH)2Cll. Beitr. Mineral. Petrog. 6, 233-?f,[7. THERMAL ANALYSIS Gnosn,S. (1985):A new nomenclaturefor the borate Two samples of New Brunswick htleardrte4M minerals in the hilgardite (Ca2BjOrCleHjiJ)- (8.02and 5.33 mg) and one samplefrom Louisiana tyretskite (Ca2B5OeOH.HzO)group. Amer. (10.63 mg) were subjected to simultaneousther- Mineral. 70, 636-637. mogravimetric and evolved gas analyses (L979)z using a Mettler TA-1 Thermoa\alyzer & Wer, C. Hilgardite' CIGA/ECA) piezoelectric pen- in conjunction with an Inficon IQ 200 quadrupole Ca2[B5OelCl.H2O:a zeolite-type taborate. Amer, Mineral. 64, 187-195. mass-$pectrometer.Typical results are shown in Figure I and in Table 5. After being subjected to a HoprNssnc, R. V. & KonN, R. (1977): Ein neues high vacuum for severalhours at room temperature, Mineral der Hilgarditgruppe: der Cl-Tyretskite von the samplesshowed weight lossesof lessthan 0.6 wt. Boulby. Kali und Steinsalz 7, 165-170, 90. Resultswere consistentfor all three samples. With a heating rate of l0"C,/minute in vacao, lwo Hunraur, C. S., Jn. (1938): Parahilgardite, a new major lossesin weightoccurred. The first loss,rang- triclinic pedial mineral, Amer. MineraL 23, 765-77 L IIILGARDITE4M FROM NEW BRIJNS'|VICK 693

(1984): The jeweler's refractometer as a Munowcrucr, B. L. (19?8): Borate investigationsof mineralogical tool. Arner. Mineral. 69, 391-398. the Sussexpotash deposits, New Brunswick,Inter- nal Report, International Minerals and Chemicals & Tevron, R. E. (1937):Hilgardite, a new Corporation. mineral species,from Choctow Salt Dome, Loui- siana.Amer. Mineral. 22. 1052-1057. Roursror, B. V. & Waucn, D. C. E. (1981):A borate- mineral assemblagefrom the Penobsquisand Salt Springs KowDnan'nve,V. A. (1964):X-ray diffraction evaporitedeposits of southernNew Brun- studies swick. Can. Mineral. of someminerulr o11trs hilgardite group. Rentgen. 19,29t-302, Mineral. Syr.Moscow ('Nedra') 4' lG18 (in Russ.). RuMaNove,I. M., Ionvsu, Z. L & Bel,ov, N. V. (197): Crystal $tructureof triclinic chilgardite[hil- MaNoenwo, J. A. (1979): The Gladstone-Dalerela- garditel Ca2[B5Oe]ClrH2O.Dokl, Akad. Nauk tionship. III. Some general applications. Car. SSSR236, 9l-% (in Russ.). Minerul.17,7l-76. WaN, C. & Gnose, S. (1983): Parahilgardite, (198la): The cladstone-Dale relationship. Ca6[B5Oe]3C1r.3HzO:a triclinic piezoelectric IV. The compatibility conceptand its application. zeolite-type p€ntaborate. Amer. Minerol, 6t, Cqn. Mineral. 19, 4/'1450. 6U-6r3.

- (1981b):Comments on the calculationof the ReceivedAugwt 28, 1985,revised manuscript accepted densityof minerals.Can, Mineral, t9, S3l-534. NovemberI, 1986,