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THE AMERICAN MINERALOGIST, VOL' 55, JULY_AUGUST' 1970

A CHLORINE-RICH BIOTITE FROM KONDAPALLI,ANDHRA PRADESH, INDIA

C. LBBr-ewaNDAM, epartmentoJGeology,Osmania IJniaersity,H yderabad,-7, ntl'ia.Assrn,{cr

A pegmatite biotite of the charnockitic region of Kondapalli, India, has a chlorine con-tent oi 1.96 petcent, the highest for an1' biotite anal-vzed to date' A chemical analysis formajor and trace elements of the biotite is presented.

INrnolucrroNCharnockites form the major rock unit of the rangesnear Kondapalliin Krishna district of Andhra Pradesh (India). They, together with a

small amount of associatedkhondalites (quartz-feldspar-biotite-garnet-sillimanite gneiss), orm a basementcomplex. A Iargenumber of pegma-tite veins occur in the area cutting the khondalites and charnockites. Aspecimen from a grey pegmatite was studied in detail with particularattention to the chemistry of the constituent biotite. The significanceofthe K/Ar age (500-525 m.y.) of this pegmatite biotite in elucidating thegeochronologicalsequenceof the Precambrian of Peninsular India hasbeennotedby Grasty and Leelanandam 1965).

GBorocrc SBm'rNcNakkal Banda is a small, flat-topped hillock extending eastwardsfrom the main Kondapalli ranges.Rocks on the northern, easternand

southern slopesof the hillock are well exposeddue to extensivequarry-ing. The eastern ace of the Nakkal Banda quarry extends or about 600feet in the north-south direction with a maximum height of 50 feet. Avariety of rock types are seen in this quarry. Acid and intermediatecharnockites are predominant; khondalites and leptynites (nonfoliatequartz-feldspar-garnet rocks, with little or no biotite and sillimanite;seealso Krishnan (1951))are essabundant; there are minor amounts ofgranitic gneisses nd migmatites; cross-cutting basic charnockite dykesand bands are present at some places. There are a few grey and pinkpegmatite veins, aplite veins and bluish-grey opalescentquartz veins'Contorted mylonite bands and rare plagioclase-magnetite ocks are alsopresent.

During the last ten years, the Nakkal Banda quarry has been inten-sively developedand the eastern working face has been advanced intothe hillock about 25 feet. The pegmatite vein, from which the specimen318 (deposited in the Harker collection-catalogue number 96299-

1353


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1354 C. LEELANANDAMDepartment of Mineralogy and Petrology, Cambridge) was collectedand studied,has unfortunatelybeencompletely emoved.

MrNBnerocy or. THDPucuerrrpThe pegmatite is an extremely coarse-grainedock with quartz, pla-gioclase, iotite and potassium eldsparas essentialminerals,garnetandore assubordinateminerals,and with trace amounts of zirconand secon-dary calcite. Plagioclase An35) ccurs n large grains, shows eeble undu-lose extinction and, rarely, reversed zoningl it possesses "transitional"structural state, as udged from its I(0.529) and B(0.896)values Smithand Gay, 1958).The potassium eldspar(Or77)s orthoclase; he separa-t ion of 130-130 nd 131 131peakson the X-ra1 'd i f f rac tometerrace szero, corresponding o zero tricl inicity. Garnet (o:11.534+0.002 A)forms rims around opaquemineralsor occursas individual grains withinclusionsof opaquesand biotite. More detailed information on mineral-ogy of the host s givenby Leelanandam 1966).Biotite exhibitsextremely trongpleochroism, ent cleavage nd wavyextinction. t has he fol lowingproperties:

I)ensitl ' 3.14A : t : 1 . 6 6 1 + 0 . 0 0 22 V " : 7 + 2Pleochroism X : l ight brownish-yellow

Y : Z : deep brownish-black.Cnnursrnv oF rHE Brorrrp ANDGENERAIDrscussroN

The biotite was separatedand purified by using the isodynamicsep_arator and centrifuging in heavy liquids. The purity of the analyzed.samplewas greater han 99.5percent.standard wet-chemical echniqueswere ollowed or the analysisof the mineral;Ti and Mn were determinedcolorimetricallyand the alkalis by flame photometry. Totar iron wasdetermined by titration with standard ceric sulphate, and ferrous ironwas determined against standard permanganatesolution. Total waterwas determinedby the Penfieldmethod and fluorine by the method ofwil lard and winter (1933); or detailsof thesemethodsseeLeelanandam(1969a).chlorine was estimatedusingNacl as the standardby eiectronmicroprobeX-ray analysis; he necessary orrectionsor absorptionandatomic number have been made (Leelanandam, 1969b). Microprobeanall'sis of cl was made on four grains, each grain being checked atseveral egions (Fig. 1); a total of twenty determinationswere made,and the valuesare remarkablvconsistent 1.96+0.03Td.r" this context,


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1355CII INRI N E-RI CH BIOT I T E

O':nN)a

a

oHR

9 t r t r x os / . F . l ! .u = ^ rd l . t r a '

M / \ / \ - ^

U

6

i s i e


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1356 C. LEELANANDAMTeer.E 1. ANarvsrs or. rnr Pncu.lrrrs Brormn (3lg) rnou KoNDApArtle

Weight percentNumbersof ions on the basisof 24 (O, OH, F, Cl) Trace elementsb(in ppm)

SiOzTiOzAlzo:FerOrFeOMnOMeoCaONarOK,oH,O(+)HzO(-)FCI

LessO=F*ClTotal

35.294 . 7 91.4 .782 0 019.25u. (r.)r0.370.000 . 1 29 . 4 rr . 7 70 . 061 . 7 rr . 9 6

101 .561 . 1 . 1100.41

i iSl)''o.206l0. 610 .234 i (o rn2 .s06s' - "0.0072.n6)- t0.03611.e051 86eJ

1.$810.842F.1e70. l7J

AITiFe3+Fe2+MnMg

CaNaKOHFC1

GaCrLiNiCoVZrScBaRbCu

60101001258014070J Z

t2502500t25

'Analysis by C. Leelanandamb Spectrographic determination bv R. Allen

biotite are presented n Table 1. The biotite containsno ca, low Mn andcombined water, high Ti , F and Cl, and more Ni than Co-featureswhich are all common to the nine analyzed.biotites rom charnockites ofKondapalli (Leelanandam, 1965). compared to the trace element con-tents of the charnockite biotites, the pegmatite biotite contains highGa and low V and Cr. The remarkably high chlorine content of thispegmatite biotite is the most noteworthy of the chemical features. Theamount of chlorine is the highest for any biotite anaryzed o date (seeDeer, Howie and Zussman, 962, Tables 12 & 13). The highestchrorine


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CHLORINE-RICHBIOTITE 1357

from the charnockites and associatedgranulites of Kondapalli containchlorine ranging from 0.14-0.62percent (Leelanandam,1965)

The high chlorine content of the pegmatite biotite has no effect onoptical properties.The refractive ndex, Y:1.661, is about the sameaswhat would be expected rom its content of FeO, FezOa nd TiO2 (seeHeinrich, 1946,Fig. 10).

The high concentration of chlorine in the Kondapalli biotites is prob-ably a reflection of environmental characteristics.No exact correlationcan be made between Cl contents of the biotites and SiOz contents (or

not any chlorine was expelled from the Kondapalli rocks during meta-morphism. The mineralogy of the pegmatite suggests hat virtually al lthe ihlorine present n the rock is effectively ocked up in the constituentbiotite.

AcrNowr,BoceMExrsThis study was carried out in the Department of Mineralogy and Petrology, Cambridge

(England), during the tenure of a commonwealth Scholarship. The writer is indebted toProfessor W. A. Deer and Dr. S. R. Nockolds for profitable discussions, to Dr' J' V' P'

the manuscript.Rr,rnnnncns

Dnnn, W. A., R. A. Howm, lro J. ZussueN (1962) Rock-Jorming Mi'naatrs, Vol" 3, Sheetsilicates. Longmans, Green & Co' Ltd., London.Gn,rsrv, R. L. nro C. LnnreNlNoeu (1965) Isotopic ages of the basic charnockite and

khondalite from Kondapalii, Andhra Pradesh, India. Mineral" Mog'35,529-535'HnrNrucr, E. Wm. (1946) Studies in the mica group; the biotite-phlogopiteseties. Ama.f . Sci'.2M,836-848.

JonNs, W. D. er.ro W. H. Hu.rNc (1967) Distribution of chlorine in terrestrial rocks. Gea-ehim. Cosmochi.m.cto,3l' 35-49.


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1358 C. LEELANANDAMKnrsnNa:.r, M. s. (1951) Bezwada gneiss, khondalite and leptynite. Rec.Gnl. Surv. Ind.ia.8l ( for 1950),315-320.Lor, D. E. (1958) A chlorine-rich biotite from Lemhi county, rdaho. Am.u. Mi,ne:ra!,.43,107 11 .LtrtaNemoAu, c. (1965) The m,i,neralogy nd petrol,og), .f he Kond.apalti charnochites. ph.D.thesis, University of Cambridge.- (1966) The geochemistry of a pegmatite from Kondapalri. J. Ind.ian Geosci. Ass.6,M-st.- (1969a) Frr0+' F and cl in the charnockitic biotites from Kondapalri,rndia. NeuesJ ahrb. M iner al., M onatsh lO, 461468- (1969b) Electron microprobe analyses of chlorine in hornblendes and biotites fromthe charnockitic rocks of Kondapalli, India. M ineroL.M ag. 37, 362-365.Surrn, J. v. eNo P. Gev (1958) The powder patterns and lattice parameters of plagioclase

feldspars, II. M ineral. M ag. 31, 7M-7 62.wrr,r,anl, H. H. exn o. B. wrNrnn (1933) volumetric method for determination of fluo-ine. Ind. Eng. Chem.,Anal,. 8d.5, 7-10.Manascri,pt rueivd., August 16, 1969; acceptd,for publ,icotion, January 1j, 1920.

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