American Mineralogist, Volume 66, pages 872-877, 1981

Karlite, Mgr(BOr)3 (OH,Cl)s a new borate and associatedludwigite from the Eastern Alps

GBRHIRo FRANZ Institut fiir AngewandteGeophysik, Petrolo gie und Lagerstiittenforschung TechnischeUniversitiit Berlin, EB 310,StraBe des 17. Juni 135 D 1000Berlin 12. WestGermanv

DTETRTcHAcrnRuaNo I nstitutJilr Mineralogie der Univ ersitiit Kiel Olshausenstr.40-60,D 2300Kiel, WestGermany

eNo EporB Kocu Mineralogisch-petrographisches Institut der Universitiit Basel Bernoullistr. 30, CH 4056 Basel, Switzerland

Abstract

Karlite, a new borate mineral with the idealized formula Mgr(BOr)r(OH,Cl), occurs in a -chlorite marble associated with ludwigite at Schlegeistal, Zillertaler Alpen, Austria. The mineral is white to light green and has a silky luster. It occursas aggregatesof minute needlesand prisms elongatedparallel to c, as much as l0 mm long, which sometimes have rosette-likeforms. Karlite is biaxial negativewith a mean 2v of 24o, a: 1.589,F: 1.632,y = 1.634,y - d: 0.045,X: c, Y : b,Z: a; and is colorlessin thin section.The (001) cleavageis perfect. The two most common forms are {ll0} and {100}. Hardnessis 5.5. is colorless. Karliteis orthorhombic,Y2r2,2r, with a: 17.929(5),b: 17.600(5),c: 3.102(l)A,Z:4, G*" : 3.02, G-.* : 2.80 to 2.85. The six strongestlines of the X-ray pattern (4 in A, in- tensity, hkl) are 2.21,100,810,740,441;2.83,92,620;2.25,87,251; 2.7g,92,260,221,540; 12.53,76,11o;an.d2.89,68, 160,221,121. IR spectraindicate that water is presentas (oH) only. DTA showsonly one strong nonreversibleendotherm at 830"C. Melting occursat 1345"C. Combined microprobe, thermogravimetricand wet chemical analysis yielded SiO2 0.02, TiO2 < 0.01,B2O3 22.92, A12O32.96, Ct2O, < 0.01,FeO 2.27,MnO 0.17,MgO 58.90,CaO 0.14,KrO 0.01,NarO 0.01,F 0.16,Cl 3.26,H2O* 10.40,HrO- 0.63 (not includedin total), total 101.22,O = F 0.82,corr. total 100.40. The mineral is named in honor of Prof. Dr. Franz Karl late professor of and petrography at the Christian Albrechts University, Kiel, West Germany; in recognition of his geologicstudies of the EasternAlps.

Introduction and petrography at the Christian Albrechts Universi- tiit, Kiel, West Germany. Prof. Karl mainly investi- Karlite was found in the Furtschaglkar near the gated the "Zentralgneis" complex of the Tauern win- Furtschaglhausin the Schlegeistal,Zillertaler Alpen, dow and gave great stimulation to geologicalstudies Austria. It occurs in calcsilicate-carbonatelenses of the EasternAlps. which are embeddedin . Type material will be preservedat the Mineral- The nineral was named in honor of Prof. Dr. ogischesInstitut und Museum der Universitat Kiel, Franz Karl (1918-1972),late professorof mineralogy Olshausenstr.40-60, D 2300 Kiel, West Germany, 0003-004x/81/0708-0872$02.00 872 FRANZ ET AL.: KARLITE and at the Institut fiir Mineralogie und Kristallo- X-ray crystallograPhy graphie, TechnischeUniversitat Berlin, StraBe des Lattice constants (see Table l) were measured 17.Juni 135,D 1000Berlin 12,West Germany.The from a small crystal with a Philips automatic four new mineral and the name were approved by the circle diffractometer and then refined by least Commissionon New and Mineral Names. squaresmethods (program PULVER,Min. Inst. TU IMA, prior to publication. Berlin). X-ray powder data indexed with the same program were obtained with a Philips diffractometer, Physicalproperties CuKa radiation, graphite monochromator,measured The mineral is white to light green, partly with a against Si as an internal standard (seeTable 2)'. brown weathering crust, and has a silky luster. It The mineralis orthorhombic,P2,2,2r; h:2n, k: forms aggregatesof minute needles and small fibers, 2n and I : 2n are the only systematic extinctions ob- sometimesup to l0 mm long, with an averageindi- served.Because ofthe large lattice constantsand rel- vidual crystal sizeof 0.5 mm by 0.002mm. It always atively low symmetry, the X-ray powder diagram occursin aggregates,sometimes in rosette-likeforms. contains a large number of lines. The indexing and At a first glanceit resemblestremolite-. refining procedurewas made with 54 lines out of 120 Hardnesswas determined by scratchingthe min- lines between5 and 75 "2e. The agreementbetween eral in a polished thin section with reference hard- measuredand calculateddata is good; but at diffrac- ness standards (Mohs scale) as 5.5. Aggregatesof tion angleshigher than 55 "20, the reflectionscould karlite were mounted on top of a needleand used to not be indexed precisely. scratch standard minerals, which gave the same re- Three reflectionscould not be indexed.They prob- sults.The hardnessof associatedludwigite was deter- ably belongto another borate phaseas will be shown mined as 5.5 as well (with the latter method only). below. Several other lines of the powder diagram Specificgravity was determinedby the suspension may belong to this phasealso. Due to the large num- method. Crystal aggregatesof I to 1.5mg gavevalues ber of possiblelines of an orthorhombic phasewith of D : 2.80to 2.85 gcm-' (6 determinations).Calcu- large lattice constantsit cannot be determined un- lation using a molecular weight of 445.00 from the equivocally to which phase they belong. The other analysisgave D : 3.02 gcm-'. Cleavageparallel to borate may be present in minor amounts only. Mi- (001) is perfect. croscopic examination of the samples which were used for powder diffractometry showed no impu- Optical properties rities. The mineral is colorlessin thin section.Sometimes Chemistry it is surroundedby a brownish rim. Figure I showsa Chemical analysiswas made with electron micro- typical aggregateof crystals parallel (a) and per- probe,wet chemical,and thermogravimetricmethods pendicular (b) to the needleaxis. {110} and subordi- (Table 3). Material for wet chemicaland TGA analy- nately are developed.Extinction is parallel to {100} sis (as well as for X-ray investigations)was obtained the needle axis, but typically undulatory. Figure 2 by crushing a bulk sample in an agate mortar; the showsthat even a crystal that looks like a true single borate phase separatedby magnetic separator and crystal consistsof small needles,oriented more or less subsequentlywashed with dilute cold HCI to clean parallel to the needleaxis. the sample from intergrown calcite and dolomite Refractive indices were determined by means of a crystals. Both X-ray diffraction patterns and IR Wifte microscope refractometer. Since it was not spectrashowed no differencesbefore and after treat- possibleto orient the crystalsproperly, only the re- ment with HCl. Thereforewe concludethat the min- fractive index parallel to the needleaxis and a larger eral is not corroded by dilute cold HCl. index perpendicular to the needle axis could be de- Thermogravimetric analysis (Analyzer Dupont termined. The third index was calculated using 2V*, 950) yielded a total weight loss between 20oC and a, and The optic axial angle was determined con- 7. 950"C of l2.l wt.Vo.Between 20oC and 1l0oC, there oscopicallywith the universalstage. It variesbetween 22" and 25" with a mean value of 23.7o.The mineral I To receivea copy of this table, order Document AM-81-166 is optically negative. No strong dispersion was ob- from the BusinessOfrce, Mineralogical Society of America, 2000 served.Optical dataarc presentedin Table I, and the Florida Avenue, N.W., Washington, D.C. 20009. Please remit optical orientation schemeis given in Figure 3. $1.00in advancefor the microfiche. 874 FRANZ ET AL.: KARLITE

Fig. l. Photomicrographof karlite (k). Fig. la is typical of the fibrous and needle like characterof the mineral. Fig. lb showsthe pseudotetragonalmorphology with {l l0} and subordinate {100}.

is a weight loss of O.63Vocorresponding to HrO-. and 22.84,r,ft.Vorespeclively. All other elementswere Gradual further weight loss takes place between determinedby electronmicroprobe. The probe stan- ll0"C and 680oCwith 0.9 wt.Vo.Thelargest weight dardswere TiO2,Al2O3, CrrOr, MgO, metallic Fe and loss occurs between680"C and 850oC and amounts Mn, wollastonitefor Si and Ca, K-Na-glassand apa- to 9.5 wt.Vo.Total HrO* is therefore 10.4vtt.Vo. Above tite for F and Cl. 850'C gradual weight loss is observed.Ignition loss In addition to karlite and ludwigite (seeoccurrence at 800"C is 10.97wt.Vo. and associations)another (borate?)phase was found BrO, was determined photometrically with by microprobe analysis, where MgO (61.47), TiO, dianthrimid and by distillation as boric acid methyl- ester.Both analysesyielded similar resultswith 22.99 Table l. Physicaland crystallographicproperties ofkarlite

a = 1.589 Cell constants

B = 1.632 17.929$)R

| = 1.634 h- 17.60o(5)8

6n= O.O4! c: 3.toz(1)B

2V*(measured) = 22o- 25o o = u= 9oo "=

Di snersi nn n^i ^hserved = 978.3 R3 -3 D (measured) :2.8o-2,8! gcm z -ll

D (calculated): 3.02 Ecn-J

Cleavage : (OO1) perfect

Color : white-green 1,,O79:11O.1,76

colorless in thin sections

Streak : colorless Fig. 2. SEM photograph of karlite showing the parallel and subparallelintergrowth of small fibers. Horizontal white bar is 2 Hardness 5.5 lrm. FRANZ ET AL.: KARLITE

is consistentwith the fact that they are too large for a unit cell where one parameteris only 3.1A. Conclusions The new mineral described here is a hydroxyl bearing magnesiumorthoborate with mihor amounts of aluminum and substituting for magnesium and with chlorine and minor amounts of fluorine substituting for hydroxyl groups. The ratio of total metallic cationsto boron is very closeto 7:3 and the empirical formula is calculated on the basis of metal- lic cations * boron : l0 as:

(MguuoAL ruFeSioMn?-*o,Cao or)2-', s2B2erO6 r,

((OH)o,Oo r.CL ozFoo+):-s -

Table 3. Microprobe analysis of karlite and associatedludwigite Fig. 3. Optical orientation scheme of karlite.

karlite Iudwigite (0.26) and F (0.33) values are a little higher than those of karlite, but FeO (0.71 ffi.qo) is signifioantly lower. AlrO, as well as Cl is absent.It is assumedthat weight-% oxides ,F this unidentified phaseproduced the non-indexedre- flections of the X-ray diffraction pattern. sio2 o. 02 o.03 IR-data and thermal study Tio2

spectraof aschariteand sussexite(Farmer, 1974)may orotal Fe = Fe); Bz1s deterTnined uet chemical; present lead to the assumptionthat BrO, may be as Hr7+ artdTr)- by TGA; n,d. = not determined well, but this is highly hypothetical. No indications H20- not included in the total' for the presenceof BOo tetrahedrawere found. This FRANZ ET AL.: KARLITE

provided that the valency compensationdue to the substitution of Al for Mg is made by O substituting for (OH) in the last pargnthesis.The ideal formula Mg,@O,)3(OH,CI)5with OH > F is preferred from the result ofinfrared spectralstudy and spacegroup requirements. From its chemical composition the mineral is similar to the nocerin (Mg.FrBOr)- (Mg, (OH,F)rBO.) series.The main differenceis the pres- ence of aluminum and chlorine in karlite. Nocerin- fluoborite is hexagonalwith a : 8.86 to 9.06A, c : 3.13 to 3.06A (Strunz, 1977).The orthorhombic cell of karlite corresponds to the hexagonal cell of noc- erin-fluoborite with 2a (hex): l8A = a (o'rh) : 17.9L, and c (hex) : 3.lA : c (o'rh); b (o'rh) : 17.6A is slightly larger than a .t/3 @ex; : 15.6A. Geologicalsetting and associatedminerals The mineral was found in a small calcsilicate marble lens (approximately I m thick and several m long) 400 m southeastofthe Furtschaglhaus,(Schle- geistal, ZilTertaler Alpen, Austria) near the path to the Gr. Moseler. The marble is embedded in am- phibolite, and this is located at the border zone between the two tectonic units "Zen- tralgneis" and 'JSchieferhtlle". A detailed descrip- tion of the mineralogy of the marble and the geologi- cal and petrologicalaspects is given elsewhere(Franz and Ackermand, 1980). It is assumedthat the high boron concentration necessaryfor the formation of karlite is due to a con- tact metasomatismproduced by Hercynian tonalitic Fig. 4. IR spectraof karlite (: A) and Mg-rich ludwigite (: n; magmas,which formed the "Zenttalgneis". The ac- from the same locality. Interpretation is given in text. Wave- tual mineral assemblage,and very probably karlite as number cm-r is plotted againstpercent transmission. well, were formed during the alpine .

exolherm 1 AT I eidotherm

Fig.5. DTA heating and cooling curve ofkarlite; dehydration occursat 830'C and melting at 1345"C. FRANZ ET AL.: KARLIT:E

Table 4. X-ray powder data of breakdownproducts of karlite troscopy. Fe'z*rich mehbers of this crystalline solid solution series(ferroludwigite and vonsenite)show a T/I'o kotoite (ASTM file No.5-0648) ODS typical absorptionband at 620 cm-'and a shifting of d hkl t /ro the bandsat 1280and 730cm-' to 1230and 705 cm-' respectively. Magnesioludwigites possessan addi- 4.23 50 koto 4.23 o20 25 4.OO o 1 1 1320 -1515 tional band at cm-'. All these characteristics 3.47 101 3.21 20 " 3.2'l 111 50 were observed in the spectrum of ludwigite from 2.67 95' 2.67 121 100 Furtschagl (Fig. a) and therefore it is classifiedas a 2.49 130 50 o31 40 magnesio-ludwigite. 2.36 25 " 2.31 2 0 1 75 220 40 The membersoT this group can not clearly be dis- 2.21 65 " 2.23 2't 1 100 tinguished by X-ray methods (Leonard et al., 1962). 2.'t8 100 " 2.18 ,:r t:o 2.11 (70) peri Refined lattice constants from diffraction powder 2.O8 102 40 data gave: a : 9.3(2);b : 12.3(2);c : 3.030(7)A, 2.O3 1O koto 2.O3 z z I t) 2.O1 1 1 2 15 which is consistent with the classification given 1.98 o 2 2 15 1.80 25 1 .80 141 25 above. 1.7 3 2 0 2 100 1.67 65 1 3 2 100 Acknowledgments 'l 1.64 3 1 1 15 .61 10 1 .6'l 1 0 5 15 We wish to expressour siacere thanks to G. Morteani for his en- | .5d U f I J) 1.55 321 50 couraging interest in this work as well as for his assistanceduring .54 o42 25 field work. W. E. Klee measuredthe IR-spectra.K. Hesseper- 1.52 35 .tl 330 100 1.49 (30) peri formed the automated four circle di-ffractometer studies, and H. .48 o13 50 Springcrthe TGA and DTA analysis.C. Tennyson,E. Foord, and 1.44 10 koto .43 3 3 1 1s A. Kato critically read the manuscript. Their help is gratefully ac- 1,41 15 .40 o50 50 knowledgcd. We want to expressour thanks to the DFG for pro- viding travel expenses(Mo 232/7) afi to the Volkswagen founda- tion for procuring the microprobe. Other minerals occurring together with karlite are References calcite, dolomite, chlorite, clinohumite, brucite, and ludwigite. The non-borate phasesare described by Alexandrov, S. M., Akhmanova, M. V., and Karyakin" A. V. group Franz and Ackermand (1980). Since the accom- (1965) Investigation of the ludwigite-vonsenite of borates by means of their hfrared spectra. (transl. Geochemistry Inter- panying borate mineral ludwigite (Mg,Fe?*), national,2, p.823-827,1965)Geokhimiya, No. 9, lll+lll8. Fe3*(OrlBOr) has not been found in the Cen- Farmer, V. C. (ed.) (1974) The IR-spectra of minerals. London; tral Eastern Alps up to now, a brief description is Mirieralogical Society Monograph 4. included. Franz, G. and Ackermand, D. (1980) Phase relations and meta- The ludwigite crystals are mostly euhedral forming morphic history of a clinohumite-chlorite-serpentine marble from the western Tauer area (Austria). Contributions to Miner- long needles of up to l0 to 50 mm length.with a alogy and Petrology,7 5, 97-ll0. rhombic cross section {ll0}, mostly 0.1-0.9 mrr Konev, A. A., Lebedeva,V. S., Kashaev, A. A., and Ushcha- wide. The crystalsoccur irregularly dispersedin the povskaya, Z. F. (1970) Azoproite, a new mineral of the ludwi- carbonate matrix as well as enriched along schistosity gite group. Zapeski VsesoyoznogoMineralogichgs-kogo Obsh- planes. chestva,99, 225-231. Leonard, B. F., Hildebrand, F. A., and Ylisidis, A. C. (1962) Under the microscope they are translucent with Members of the ludwigite-vonsenite series and their distinction strong green-redbrown pleochroism or are nearly from ilvait. Petrological Studies Geological Society of America. opaque.Partial chemicalanalysis (see Table 3) shows (Buddington Vol.), 523-568. that it is a Mg-rich member of the ludwigite-vonse- Struna H. (1977) Mineralogische Tabellen. AkademischeVer- lagsgesellschaftGeest + Portig, Leipzig. nite group. AlrO, contents are low (about I vtt.Vo). According to Alexandrov et al. (1965)the minerals of Manuscipt received,fuly 2, 1980; this group can be distinguishedby meansof IR-spec- acceptedforpublication, February 16, 1981.