Zincian and Manganoan Amphiboles from Franklin, New Jersey1

THE AMERICAN MINERALOGIST, VOL. 53, JULY.AUGUST, 1968

ZINCIAN AND MANGANOAN AMPHIBOLES FROM FRANKLIN, NEW JERSEY1

ConNBr.rsKrurN, Jn. aNo JuN Iro,2 DepartmentoJ Geological Sciences, H of mon Laboratory, H araard U nioersi.ty, Cambrid.ge, M assochusetts.

Assrnecr Zincian and manganoan amphiboles occur locally as coarse-grained, irregular massesin the skarn zones of the Franklin orebody. These amphiboles are associated mainly with calcite, rhodochrosite, rhodonite, tephroite, andradite, willemite and franklinite. Chemical analyses, optical and X-ray parameters, and assemblage descriptions are given for three cummingtonites, nine members of the tremolite-actinolite series and one magnesioriebeckite. The cummingtonites show maximum ZnO and MnO contents of 10.8 and 13.79 weight perceDt respectively (1.22 and 1.83 atoms/half unit cell); members of the tremolite- actinolite series contain smaller amounts of ZnO and MnO, the maxima being 9.54 and 5.42 weight percent respectively (1 04 and 0.67 atoms/half unit cell); a magnesioriebeckite con- tains 7.84 weight percent ZnO and,4.16 weight percent MnO (0.86 and 0.81 atoms/half unit ceII). INrnopucrroN In his study of Franklin minerals, Palache (1937) reported the analysis and optical parametersof a zinc-rich cummingtonite (seeTable 1, no. 89365),but no other zinc-rich amphibolesare describedin the literature. Manganoan amphiboles are much more common in nature and have been studied by various authors (Sundius, 1931; Yosimura, 1939; Bilgrami,1955;Jaffe et al., 196l; Segeler,1961; Matkovskiy, 1962;and Klein, 1964and 1966). The amphiboles of this study are of interest becauseof the large and variable amounts of Zn and Mn2+ that are present in their structure. These amphiboles which include members of the cummingtonite-grunerite series,of the tremolite-actinolite seriesand one magnesioriebeckite, occur in the skarn zones of the orebodiesat Franklin. They are part of Zn- and Mn-rich assemblageswhich consist of rhodonite, tephroite, franklinite, willemite, calcite, rhodochrosite and other minerals. The specific assemblagefor each amphibole is given at the bottom of the chemicalanalytical tables (Tables 1, 3 and 5).

Cnnlrrcal ANAr,vsrs,Orrrcar, X-RRv AND SpECrnc GRAvrry Dnron- MINATIONS

Four of the amphiboles, cummingtonite no. 90384, actinolites no. 2 and 3, and magnesioriebeckite no. 89407 were analvzed bv Tun Ito usinq a combination of wet chemical

I Mineralogical Contribution No. 446 2 Present address: Inorganic Materials Division, National Bureau of Standards, Wash- ington, D. C. t264 ZINCIAN AND MANGANOAN AMPHIBOLES 1265

T,q.sln 1. Cnrurclr ANer-vsrsor CUMMTNGToNTTE

90384 90391" 89365

SiOr 53.6 51.5 49.71 AlzOa 0 r.72 FezOe .35 FeO 3.50 t2.9 12.80 MnO 12.9 t3.2 13.79 ZnO 6 .9.5 10.8 10.46 Mgo 16.9 11.1 8.31 CaO 1.66 .1 .49 1 NaaO . /J .22 KrO .17 n.d. n.d. H,O(+) 2.35 n.d. \2.ro HrO(-) .18 n.d. ) F n.d.b n.d.

Total 99.82 99.7

Number of ions on the basis of 24 (O,OH) 23 oxygens 24 (O,OH)

qrl Si 7.871 7.sz\n I' ;;i8.00 AI .oe)7.e6 -) . '".,j I AI -j -t .r2l Fd+ .07.l -l -l Fd+ '^-lLll 1.6s1 1.681 Mn 1.601 r.721 1.$l Zn .7s f7 .03 L.221719 1.2116.ss Mg 3.701 2.s41 1.9s1 Ca .261 .02j .081 Na -2rl MJ .061 K .02) -) OH 2.30 2.25 100 Mg/oag+nel 88.2 60.6 J.t.o 100Mg/1MgaF"$roaz"1 56.5 35.6 29.2 100Mn/1yg1r"arr,y 27.6 29.r 33.6 lOOZnfrue+t +znl 15.2 22.5 25.O

Assemblage90384: cummingtonite (light green, very coarse masses) -franklinite-calcite- tephroite-willemite (along cleavage planes in tephroite)-hendricksite. cummingtonite analysis by J. Ito. Assemblage90391: large, anhedral, single crystal of willemite (6'X4'X2') with very fine grained, fibrous intergrowth of cummingtonite; trace of franklinite. Assemblage 89365: cummingtonite (large masses)-rhodonite-schallerite-willemite- serpentine-hendricksite (trace). Specimen shows evidence oI strong shearing and brecciation. Cummingtonite analysis by Bauer (Palache, 1937).

' Electron probe analysis. b n.d.:not determined. 1266 CORNELIS KLEIN, JR. AND JUN ITO and spectrophotometric techniques. Essentially monomineralic samples of these four amphiboles were crushed to between 50 and 120 mesh, and were subsequently purified by hand under a binocular microscope at X30 magnification. The grains were carefully scanned and those which showed inclusions or other adhering phases were removed with a needle. The resulting samples that were submitted for chemical analysis were estimated to have been 99.8 percent pure or better. optical, X-ray and specific gravity measurements were made on a separate part of the analyzed. sample. AII other analyses were made by C. Klein using an ARL-EMX (Applied Research Laboratories) electron microprobe. Handpicked grains were anaryzed in carbon-coated polished sections, except for cummingtonite no. 90391 which was analyzed in polished thin- section. The analysis conditions were: 20 kilovolts accelerating potential, 0.03 microampere sample current, 3- to S-micron beam size and ten seconds counting time. The four chemically analyzed amphiboles of this study and ten other chemically analyzed, amphiboles were used for the construction of standard curves (see Klein 1968, for reference to standard sampies and standard curves). Approximately ten data points were taken on each standard and each unknown, each da|a point was repeated once, and the count values were averaged. No chemical zonarion or exsolution was detected in the samples. The morimum relative error in the weight percent values for SiO2, Al2Oj, FeO, CaO and MnO is estimated to be 'fhe approximately + 2 to 3 percent oI the amount present. mar,imum relative error in the MgO, Na:O and ZnO values is probably f 5 percent of the amount present. X-ray diffractometer charts were obtained for all samples with filtered FeKa radiation (l-9372s A) using high-purity silicon as an internal standard. The mixture was mounted as a very thin coating, approximately 1/10 mm thick, on a glass slide using a solution of col- lodion and isopentyl acetate as a binder. Two recordings were made, one in ascending and one in descending mode, with goniometer and chart speeds of l/4" per minute and l/2inch per minute respectively. The peak positions were measured directly on the graph paper to O.OI" 20 and were located with respect to the silicon peak positions. Whenever difierences in peak positions were observed in the ascending and descending modes, the average of the two values was taken as the final 20 value The diffraction peaks were indexed by compari- son with indexed patterns in the literature (Comeforo and Kohn, 1954; Ernst, 1960; and Klein and waldbaum, 1967). Approximately fourteen unambiguously indexed difiraction lines were used in a least-squares refinement program (Burnham, 1962) for the calculation of the unit-cell parameters. The indexing and unit-cel1 parameter calculations were done on the basis ol a C2/m space group. Dr. Malcolm Ross of the U. S. Geological Survey, Wash- ington, D. C. kindly verified the C2f m symmetry for three of the samples (cummingtonite no. 89365, actinolite no. 2 and magnesioriebeckite no. 89407) with (h\I) and (0fr1) preces- sion photographs. The refined unit-cell parameters were used in calculating the density values, rndices of refraction and extinction angles were determined by means of a spindle stage (wilcox, 1959) using a sodium light source. The refractive indices are estimated to be ac- curate to *0.001 and the extinction angle measurements to t1o. Axial angles were cal- culated from the expression:

1.an2v,:' /1_1) / (L_!\. \a2 B'/ / \p' 12/ Specific gravity determinations were made with the Berman Microbalance using 20 to 25 mg samples of minus 50- to 100-mesh grain size.

CulrurrqcroNrrB The zincian and manganoancummingtonites at Franklin are light to medium green in color and occur in irregular massesin the skarn zones. ZINCIAN AND MANGANOAN AMPHIBOLES t267

Their green color is very similar to that of members of the tremolite- actinolite seriesand the manganoan cummingtonites describedby Klein (1e64). The chemical analysesfor three cummingtonites, arranged in decreas- ing Mg-content, are given in Table 1. The complete analysesfor samples no.90384and no. 89365are recalculatedon the basisof 24 (O, OH), and the electron probe analysis for sample no. 90391 is recalculated on the basis of 23 oxygensbecause the HzO content was not determined.A re- calculation on the basis of 23 oxygens is possible because the FezOr component in the cummingtonite-grunerite seriesis very small or non- existent. Although the Mg, Fe2+and Zn contents vary considerably, the Mn content is similar in all three samples,and rangesfrom 1.60to 1'83 Mn atoms/half unit cell. The Zn content is highest (10.8weight percent zto) in sample no.90391, in which the cummingtonite occurs in very intimate intergrowth with willemite, but willemite is present also in the other assemblages(for assemblagedescriptions see the bottom of Table 1). The cummingtonite in sample 90391 occurs as numerous, very fine, slender needleswithin a large single-crystal of willemite. The c-crystallographic axis of the needlesis parallel to the c axis of the enclosingwil- lemite. Figure 1 illustrates this occurrence. The relatively large Mn2+ ion (0.80 A in sixfold coordination, Ahrens, 1952)probably substitutesmainly in the M(4) positionin the amphiboles (correspond.ingto X in the general formula XzY5Z8O22(OH)z;for notation see Ghose, t962). Ln approximate limit of 2 Mn2+ ions out of seven cations per formula was suggestedby Klein (1964).The Zn-contentin the cummingtonites varies from 0.75 to 1.22 Zn2+ ionsfhalf unit cell. As the ionic sizeotZn (0.74 A; it ttte same as that of p"z+ (0.74 A) and fairly similar to that of Mg (0.66A.1,Zn is probably housedmainly in the M(1)' M(2) and M(3) cation sites. The unit-cell parameters (given in Table 2) of these cummingtonites are very similar to those of the manganoan, zinc-fueecummingtonites given in Klein (1964). The 6 dimension of cummingtonite no. 90384 is considerably smaller than that of the more Fe-rich cummingtonite no. 89365. The specific gravity of cummingtonite no. 90384 is similar to that of zinc-ftee manganoan cummingtonites (Klein, 1964), whereas that of cummingtonite no. 89365is considerably higher and more in the range of that of Fe-Mg grunerites. The optical properties, given in Table2, are similar to those ol zinc' free members of the cummingronite-grunerite series. AII three samples show multiple twinning parallel to (100). Becauseof the similarity in the physical properties of these amphiboles with those of zinc-free members of the cummingtonite-grunerite series Frc. 1- willemite-cummingtonite intergrowth (assemblage no. 90391) in thin section cut perpendicular to the willemite c axis. cross polarized light. The willemite is dark (in extinction), the cummingtonite light colored. Although the c crystallographic axes of the willemite and cummingtonite are parallel, the a and b axes of the cummingtonite are randomly oriented with respect to the willemite. Magnification 100X.

Treru 2. Prrysrcar Pnoprnrrns or CuuurNcroNrrn (Srecn Gpovp C2/m)

90384 90391 89365

o,A 9.587+.001 9.577+.001 9.575+.003 b,A 18.101+.002 18.217+ .oo3 18.229+.OO4 5.315+.001 ",it 5.327+ 001 5.327+ .003 0, deg. 10260 +.01 102.13+ .01 102.21+ .O3 v (A') 900.16+ .25 908.71+ .28 908.74+ .63 ,D (calc) 3 .25 3.M Sp. Gr. (meas.) 32++.O2 3.44 X .O2 ^l 1.660 r.682 1.685 r.647 |.670 1.674 q 1.634 1.654 1.657 ^Y-4 .026 .028 .028 zAc 200 11" 15. 2V, calc 90"41' 98'56' 103.04' 2V^, meas 105"+ 2" Colorless and non-pleochroic ZINCIAN AND MANGANOANAMPHIBOLES 126<) and becauseof their likenessin color to membersof the tremolite-actinolite series, the presence of manganese and zinc must be established chemicallv.

TnrlrorrrB-ActrxorrrB Nlembers of the tremolite-actinolite seriesvarv frorn very light beige, for tremolite no. 4, to medium and dark greenfor the actinolites.These in calcic amphiboles occur sporadically in irregular massesand stringers the skarn zonesof the orebody.Many of the assemblagesshow evidence the of brecciationand shearing.The amphibolesare frequently bent and with associatedfranklinite and garnet crystals are sheared and broken, 3 for the interstices fiiled with carbonate (see the bottom of Table specificassociations). The assemblagesin which the tremolite and actino- lile occur are much more calcic and less zinc-rich than the cumming- present tonite-bearing samples.calcite, rhodochrosite and rhodonite are found in large amounts in most of the assemblages,whereas willemite is only in trace amounts in a few of them. are Th. urrulyr.s of nine members of the tremolite-actinolite series given in tatte S. The complete, conventional analyses are recalculated of on the basisof 24(O,OH) utd th" electronprobe analyseson the basis of 23 oxygens. Although as much as 25 percent of the total Fe content the actinoHlemay be presentas Fe3+(Deer, Howie, and Zussman,1963) total iron contents of the analysesin Table 3 are so small (max. 5.4 wt' /6 present as FeO) that the error introduced by assuming all the iron to be in FeO only, is negligible. The manganeseand zinc contents are similar all the analyses except for tremolite no. 4 which has a considerably oc- lower Zn content than the actinolites. Yosimura (1939) described currences of manganoan tremolite (7.38 wt'/6 MnO) and manganoan of the Kaso actinolite (5.79 wt. ToMrnO) from the manganesedeposits to be present in the Mine in Japan. Zinc, however' was not reported analyses. (Ca*Na In the majority of analysesin Table 3 the total number of rangesfrom 1'69 *K) atoms/half unit cell is considerably below 2'0 and error but is to 2.05. This apparent d'eficiencyis not due to analytical positions in caused by the assignmentof the atoms to the various cation Mn2+'and the structural formula. Undoubtedly lhe majority of the position probably some of the Fe2+ions should be assignedto the M(4) connec- to make the total number of ions 2.0. It should be noted, in this M(3) and tion, that the toral number of cations in the M(l), M(2), ,4r'(4)positions calculates to close to 7 in all analyses' for the The unit-cell parameters, specific gravity and optical data parameters tremolite and actinolites are given in Table 4' The unit-cell 1270 CORNELIS KLEIN, TR. AND IUN ITO

Tesrr 3. Cnrurcer ANervsrs or,Tnrltor,rrr aNo Acrrnorrre

SiOz JJ/ 54.4 51 2 53.9 AbOr U o6i 03 0.4 0.4 FerOi 152 FeO o7 223 39 40 40 MnO 4.1 542 4.6 4.9 40 ZnO 8.99 8.4 85 88 MgO 2t2 146 15.4 146 14.6 CaO 107 9.88 9i 10.7 106 Na:O 0.9 t.4 06 13 K:O ndb 0.10 nd nd nd HrO(*) nd nd nd. n.d H,O(-) nd nd nd. nd. F nd nd, nd nd n.d

Total 97.6 99.71 98 1 979 97.6

Number of ions on the basis of 23 oxygens 24 (O,OH) 23 oxygens 23 oxygens 23 oyxgcns Si *'1,,, 'lf)'." '.3$'.*'31)'* ' AI 3i)', AI -1 Fer+ -l .16 Fc:+ .08,1 27 fs 48 Mn .481 .67 Zt .441 734 -97 Mg 4.48) 324 Ca r.62J 1.55 Na .24i1.86 .12 K 02

OH 230

1o0Ms/(Ms+Fe) 983 88.1 87.6 868 868 1o0Ms/(Ms+Fe +Mn*Zn) 817 60.6 63.4 61.3 62.3 100Mn/(Ms +Fe+Zn) 9.6 15.6 12.8 14.2 11.8 r\ozn/ (Ms+Fe +Zn) E9 211 191 199 20.5

Asserublageno. 4.. tremolite (light 'Ihe. beige)calcite_rhodochrositeband in host rock of franklinite and calc.ite. tremolite is sepamted from the franklinite by the carbonates. no - .tlssmblage 2: acti\olite (green,very coarsegrained)-calcite minor sphalerite and a trace of willemite. Actinolite analysisby J. Tto. Assmblage no.7j actinolite-calcite-quartz-rhodonite and a trace of sphalerite. Assmblage m. 9C: actitolite-rhodochrosite-calcite-franklinite-mbnganoan 'I'he andradrte-quartz-microcline. specimen shows evidence oI brecciation, Assembl'ogeno' 5: actinolite+alcite-manganoan andradite. This speiimgn showsevidence oI severeshearing and brcciation, ZINCIAN AND MANGANOAN AMPIIIBOLES 1271

Tqgr,n 3 (cont'il'\.Clrcmical Analvses oJ Tremol'iteand Actinolite

52 8 SiOr 53.3 090 Al:O. t6 2.92 FeO: 3.56 FeO 424 MnO 46 9.54 Zn() 85 l2.5 Mgo 137 903 CaO 107 1.80 NarO 09 .30 KrO n.d. 2.56 H,O(+) n.d H:O(-) nd. nd n.d F n.d

'Iotal 987 100 15

Number of ions on the basis oI: (O'OH) 23 o{ygens 23 oxygens 23 orvgens 24

t oo-|r.oo 7.&l Si ':3i)' 800 'i:,1,* AI oo .r7)

AI Fer+ Fe2r tr1, Mn Zt Mg Ca 1.68\ l '3j Na .2s) K .0sI 2.52

861 860 81 9 78.5 60.7 62.5 58.3 54.3 13.6 12 4 13.4 13.0 20 7 19.0 20.0 22.8

A ss mbl og e no. 8 : actinohte-serpentine-rhodonite-calcite-rhodochrosite' Assmbl,ageno. 1: actinolite-rhodonite-calcite,with tracesof willemite and franklinite' The franklinite is highly Assmbtagezo. d..actinolite-franklinite-calcite-rhodonite and traces of willemite brecciatcd. and brecciated Asswbl,age rro. Ji actinolite-franklinite-calcite-manganoan andradite. Highly deformed minerals. The actinolite analysis is by J' Ito.

s electron probe analYsis. n.d *:not determined. t272 CORNELIS KLEIN, JR. AND JUN ITO

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L o99g: '6 +t +t +t +l +l E €NN OO+6 sooo+ +d:N @oNb+ €€€o O@b

g'3.lrl?,i g .<"<"< ? i(s- ddda'lAdd ia. d }N-NNN X ZINCIAN AND MANGANOAN AMPHIBOLES r273

'.ferrn 5. Cxurrrcer,Axer,vsrs eNn Prlvsrcar-Pttoprnrtns ol MecNrsronrnnrcxrrn Nr'l. 89407

wt 7o Number of ions on basis of 24(O'OH)

sio: 53.0 Si 7.861-'"t^- Alzor .58 AI .osJ', Fezos 9.64 AI FeO 3.18 l'e3+ 1.07] lvlnO 4.16 Fd+ ZnO 7.84 Mn Mgo 11.0 Zn CaO 2.63 Mg NarO 5.30 Ca KrO .28 Na Ir.oz H,O(+) K .M) H,O(-) OH 2.28 F

Total 100.04 100Mg/rMe+r"r :62.5 x n.d.:not determined;Jun Ito, 100Mg/1yg1r.an"az"y :46'2 analyst. 100Mn/1yg1r"+Mn; : ll .7 l\jZnf

Assembtrage: magnesioriebeckite (coarse-grained, dark green)-rhodonite-Iranklinite- calcite-serpentine. are very similar for all samples, but the optical indices show a definite rise with increasing Fe-content.

MacNBsronrEBECKrrE The chemical analysis and physical properties for magnesioriebeckite no. 89407 are given in Table 5. This sodium amphibole is very dark green, almost black, and occurs as coarsely crystalline massesclosely intergrown with rhodonite, calcite and franklinite. The MnO content (4.16 weight percent) of this magnesioriebeckiteis less than that of the magnesioriebeckite(5.9 weight percent) coexisting 1274 CORNELIS KLEIN, ]R. AND JUN ITO with a manganoancummingtonite, reported by Klein (1966).The ZnO content of 7.84 weight percent is somewhat smaller than that found in the actinolitesof Table 3. As in the actinolites,some of the Mn may well be presentin the M(4) position and the Zn probably substitutesfor the Fe2+and Mg in the M(l), M(2) and M(3) sites. The unit-cell parametersof this magnesioriebeckiteare very similar to those reported by Borg (1967) for end-membermagnesioriebeckite (Na2Mg3Fez3+Sisorr(OH)).The.y and B refractiveindices are alsosimilar to that of the end-membercomposition but the a index of the manganoan and zincian variety is higher than that for the pure Fe-Mg end-member. As in the caseof the other zincian-manganoanamphiboles the assemblage makes one suspecta certain amount ol Zt and Mn substitution in the amphibole;the physicalproperties, however, do not provideconclusive evidence.

ACKNoWIEDGEMENTS

The authors are grateful to Professor Clifiord Frondel for making the Franklin material available for study, and for his continued interest in the results Dr. Malcolm Ross, U. S. Geological Survey, Washington, D. C. is gratefully acknowledged for verifying the space gonp (C2/m) of three of the conventionally analyzed samples by single-crystal techniques. This study was supported in part by National ScienceI oundation grant no. GA-1085.

RornnnNcns 'I'he ArrnnNs, L. H. (1952) use of ionization potentials. I. Ionic radii of the elements. Geochirn.Cosmoehim. Acta, 2, 155-169. Brr.cna.ur, S. A. (1955) Mn amphiboles from Chikla, Bhandara District, India. Mi,neyal Mog , 3O, 633 644. Bonc, L Y. (1967) Optical properties and cell parameters in the glaucophane-riebeckite sertes. Contr. Minerol,. Petrology, lS, 67-92. BunNnan, C. W. (1962) Lattice constant refinement CarnegieInst. Wosh. Veor Booh., 61, 732-13+. Counrono, J. E. lNo J. A. KouN (1954) Synthetic asbestosinvestigations I Study of synthetic fluor-tremolite. Amer. Mi,neral.,39, 537-549. Dnnn, W. A., Howrn, R. A., nNo Zussuew, J (1963) Roch Jorming minero)s, ool. 2,lohn Wiley and Sons, New York. EnNsr, W. G (1960) Stability relations of magnesioriebeckite. Geochim. Cosmochim. Acto, 19, 10-40. Gnosa, S. (1962) The nature of Mg2+-Fe2+distribution in some ferromagnesian silicate minerals. Amer. MineroL. 47. 388 394. Jarlr, H. W , W. O. Y. GnonNrwr,n-Msynn nNo D. H Sor,cnow (1961)Manganoan cummingtonite from Nsuta, Ghana Amer. Mineral ,46,642-653. Kr.rrN, C. (1964) Cummingtonite-grunerite series; a chemical, optical and X-ray study. Amer. Mineral . 49. 963-982. --- (1966) Mineralogy and petrology of the metamorphosed Wabush Iron Formation, south westem Labrador. J. P etrology, 7, 246 305. --- AND Watoe,luu, D R. (1967) X-ray crystallographic propertics of the cummingtonite-grunerite series. -/. GeoI.,75, 379-392. ZINCIAN AND MANGANOAN AMPHIBOLES 1275

--- (1968) Coexisting amphiboles. J. Petrology (in press). Marrovsrrv, O. I. (1962) Dannemorite from the Chivchin Hills in the Carpathians. DokL Akad..l[oz& SSSR, 146, p. 893-896. [Trarsl. DokI. Acod..Srl. [/SSR., Earth Sci.. Sec. (1964), 146, 125-128.1 Par.ecnn, C. (1937) The minerals of Franklin and Sterling Hill, SussexCounty, New Jersey, U. S. Geol. Suns. ProJ. Pap. L8O. Srcrr.nn, C. G. (1961) First U. S. occurrence of manganoan cummingtonite, tirodite. Amer. Minual,., 46, 637-641. SuNorus, N. (1931) The optical properties of manganese-poor grunerites and cummingtonites compared with those of manganif erous members. Amer . J . Sci., 21, 330-3M. Ycsruuna, T. (1939) Studies on the minerals from manganese deposits of the Kaso Mine, Japan. f . Fac. Sci..Hohhaid.o Unht.,4,313-452.

Monuscr'ipt receiaed.,October 9 , 1967; accepteilfor publication, J anuary 9, 1968.