Canadiaii Mineralogist Vol. 17, pp.47-52 (1979) AFGHANITE: NEW OCCURRENCESAND CHEMICAL COMPOSITION DONALD D. HOGARTH Depfftmenl ol Geology, (Jniversity ol Ottawa, Ottawa, Otttario I(IN 6N5 ABSTRACT broadly distributed in occurrences of southwest Baikalia." Afghanite has recently been identlfied ejecta in pumice from Afghanite has been identified and analyzed by in silicified limestone (Merlino & Mellini microprobe in lapis lazuli from Lyadzhuar- Pitigliano, Tuscany, Italy Darinsk, U.S.S.R. and Edwards, New York, U.S.A., 1976, Merlino & Orlandi 1977b). bringing to five the number of known occurrences During a study of the petrogenesisof lapis of this mineral. A new analysis of a specimen lazuli, afghanite was positively identified in from the type locality, Sary-Sang, Afghanistan, specimenstaken from three different localities. leads to the idealized formula 4[AaBtO"nX"], wit}r Two of these (Edwards, New York and Lyad- - - - I Na, Ca, K; B Si, Al; X SO{, Cl, COg. zhuar-Darinsk, Pamir, U.S.S.R.) are new The role of H has not been established. Compared localities for this mineral; Edwards is the first group, afgha- to other members of the cancrinite reported North American occurrence. The in K. nites tend to be rich in Ca but depleted the type locality, Sary- l:1, but little Cos. The rela- other specimen is from They have SOa:Cl= properties conform tionship of natrodavyne and magnesium-cancrinite Sang. Optical and chemical was to established members of the cancrinite group is with afghanite but the final confirmation uncertain. made by X-ray diffraction photographs taken with a Gandolfi camera. The pattern closely matches that of type afghanite and include Sorvrrvrernr diagnostic lines with spacings of 6.05' 5.35 and 4.00A which belong to afghanite but not On a identifi6 et analys6 I la microsonde I'afgha- to cancrinite, davyne or microsommite (Bariand nite du lapis lazuli de Lyadzhuar-Darinsk (U.R.S.S.) et al. 1968). In all specimens, the afghanite et d'Edwards. N.Y. (E.-U.), ce qui porte ir cinq le is rather fine-grained and too impure for single- nombre d'endroits otr ce min6ral a 6t6 rep6r6. De crystal X-ray studies. plus, une analyse nouvelle de l'afghanite faite sur In addition, a mineral, very likely afghanite, Sary-Sang (Afgha- sp6cimen de la localit6-type, was noted in other thin sections, but identifica- nistan), mEne i la formule id6alis6e lAsBL2OrAXt) tions rest on optical properties alone. These A - Na, Ca, K; A - Si, Al; X = SOa, Cl, avec cut from lapis lazuli of CO". Le r6le de l'hydrogdne demeure obscur. En thin sections were (2 comparaison des autres membres du groupe des Lyadzhuar-Darinsk additional specimens), cancrinites, les afghanites sont riches en Ca et Malo Bystrinski, Lake Baikal area, U.S.S.R. pauvres en K, avec rapport SOa:Cl proche de (1 specimen) and the main lapis lazuli oc- I'unit6 et faible teneur en COa. Quoique les autres currence, Lake Harbour, Baffin Island ( I spe- membres du groupe aient aussi des compositions cimen). 'etcaract6ristiques, leur relation avec la natrodavyne la cancrinite magn6sienne reste incertaine. (Traduit par la R6daction) Occ'urnnNcn The Afghan specimen (no. 5) contains well- INrnooucttox formed thin tabular crystals of afglanite (about 1% by volume) that cut through lazurite in Afghanite is an uncommon mineral related several directions; at least two of these seem to cancrinite, first described from a specimen to be in a preferred orientation (Fig. 1) with of lapis lazuli from Sary-Sang, Afghanistan {0001} laths of afghanite forming a dihedral (Bariand et al. 1968) and later from lapis lazuli angle of 60o. The laths do not extend beyond of the Lake Baikal region, U.S.S.R. (Ivanov & the lazurite grains. Common associated min- Sapozhnikov lns). According to the Russian erals are phlogopite, diopside and oligoclase. authors, afghanite was identified from the Pamir specimen no. 4 contains approximately Tultui and Malo Bystrinski deposits by "further 13 vol. % afghanite. Crystals are stout to studies that showed that the mineral was slender tabular; in some clusters, they are 47 48 THE CANADIAN MINERALOGIST Oprrcer, Pnopnnrrss Bariand et al. (1968) and Ivanov & Sapozhnikov (L975) have shown that, in thin section, afghanite is colorless, uniaxial posi- tive, has low-order interference colors and low relief. It lacks good cleavage and may show conchoidal fracture. With such quartz-like prop- erties the mineral could possibly be confused with quartz itself, particularly where isolated in diopside and present in anhedral grains as at the Edwards mine. This mayo at least in part, explain reports of quartz-lazurite associa- tions (e.9., Fersman 1920, Voskoboinikova 1938); otherwise, a free silica-feldspathoid as- sociation is difficult to understand. Quite possibly, some minerals in lapis lazuli, identified optically as natrodavyne, may also be 'onatrodav)me" afghanite. Thus from the Slyudyanka region gave or = 1.525, e = 1.530, A =0.0053 (S,mirnov 1928); the Lyadzhuar-Darinsk material gave a = I.522, e = 1..528,A = 0.0O5 (Yudin et al. 1.932). Type natrodavyne from Vesuvius has al = 1.5220, e = 1.5267, A = 0.0047 (Zambonini 1910). However, the quantities of certain chem- ical constituents reported by Zambonini are questionable. For example, SOs wos found by difference and IGO, apparentlyo was not de. Frc. 1. Thin tabular afghanite(A) in lazurite (L). termined. The status of this mineral is there- Other mineralsare diopside(D), oligoclase(O) fore uncertain. qnj.nhlgsooite_(P). Specimen5 from Sary-Sang,-l Afghanistan.Crossed polars, bar scale= mm. TAgtE t. ffiiltru @lpostTro{ 0r AteHNtTr LLg.tr.o !l9z 30.8 2s,9 32.10 3l.o 31.95 32.96 present al.most to the exclusion of lazurite. I!O: n.d. n.d. B.D. n.d. 8.0. ;:;:- lrao, 2s 23.a 27.@ 2s.2 ia:48 iiis Afghanite and lazurite-afghanite clusters are n.d. n.d. n.d. n.d. 8.0. B.D, !s! !:dr n.d. B.D. 0.03 B.t. B:D: surrounded by diopside. c.0- !q.5 11.4 lz.i4 ll.7 i1.66 ii:tg !"?0 1?.9 02.6) t2.43 t3.3 ir.i6 1,:6, Af.ghanite occurs !:o 2.7 2.a 0.86 2.2 ,.6n a:ot in a similar crystal habit !9s s.s 0.3 9.6€ lo.s ro.s9 10.62',:rs and mineral pamir cr 4.6 s.5 4.54 3.6 .i:ia association in the two other l- '!.4. n.d. 0.035 n.d. 0.04 ;:;: !0? 0.4 n.d. 0.76 n.d. n..t. n.d. specimensobut in very minor amounts. Tabular HrO O.7 tr.d. 2-11 afghanite was identified (about rorr err roT:6s #S toFii t#* l0/o of. tha oscl,F 1.0 1.2 1.05 o.At t.m 0.m thin section) in a diopside-phlogopite-lazurite- ret ss-:r ld:&r giE? roo=ji ,g:6d calcite rock from Malo Bystrinski, Lake Baikal, Ions b!.6d on l2 (St . Al) U.S.SrR. !'llrz.oo!'!!fra.m !:3$'"* !.S'r.*!:fff',.*!.!$'2.* Lapis Fel -l 0.001 0,001 lazuli specimen no. 6 was collected rsl _l _l 0.q 0.orl o.ool rool from,the Dl sphalerite orebody, Edwards mine C!e r.safe.or3.ete.83 2.4+i.2t 2. sl9,@ 2.3h7.& 2.4511.8j (St. Joe Minerals ttaI 4.861 s.fsl 4.s4 s.o3l n.ol o.rrl Corporation)o Edwards, New (l 0.691 o.zsl o.zrl o.srl 0.631 0.751 York. Major minerals are pargasite, diopside, s0{ r.3rl t.361 1.541 r.5q t.551 oligoclase and lazurite. Afghanite amounts to cll 1.55 1.961 r.441 l.r9l r.{ol r.agl 't -l 13.27 [email protected] -l 12.73 0.d2.8 l2.u about l/a by volume. Its habit is somewhat dif- c0d oJl o.'gl _t-l ferent than in the Pamir and Afghan sections: 0 25.21 ?5.63 23.17 24.21 23.88 21.6 Hzo 0.45 l.? rounded grains lack crystal outline and are 't.529 '1.5331.528 commonly separated from lazurite. 1.528"*, A few 0.ffi 0.005 0.@55 grains of tabular afghanite are also present in l. !6ry-Saq,4lgbnlsBni amlsts ontSO s9 by'rb2oJ. Frtrsche (Bartand at at, lg8l, the thin '' ercrcprcbean,lvsis va)ue116o amr5ls i sestion. Hlifilt;,Tg3Tl:3ini The Baffin 3. fultul-deposlt-nflrfultul deposlt n!!r lake Bal&at, u.S.S.R.U.S.S.R. f.A. neptkoya, a@tj6t (lvamv ! Island afghanite appears as S!@zhnflov 1975). rounded isolated grains 4. Ly.dzhulr-Darlnsk, Pul., U.S.S.R.i Etcrcprcbo snrtysls by t.L. Grtffln, oslo. in small amounts in ?. !.ry-sng, arghnrsEni ntcrcpmh arulSts by p. ibtun, otBm. 6._EdEds, k Yorki dtcrcpftb€ 8illy3t9 by p. torbn, otbra. nepheline, associatedwith diopside aud lazurite. !.u.l mrd detftttoni n.d.: et &Emlnd. NEW OCCURRENCES OF AFGHANITE 49 Refractive indices and birefringences of more potassic. However, note that whereas afghanite are listed at the bottom of Table l' cancrinites a'nd afghanites come from world- wide localities, microsommites and davynes are all from the Mount Vesuvius area and analyses Cnvsral CHEMrsrRyoF THECeNcnlNrts Gnour are oldo mainly of 1873-1878 vintage. Two analyseswarrant special mention. Num- A review of the literature suggeststhat in- bers 8 and 9 are 'omagnesium-cancrinites"from dividual members of the cancrinite group have St. John's Island, Egypt; they contain 8.71 and rather distinctive coinpositions.To explore these 9.9Qo/o MgO, respectively (Spencer 1923, El peculiarities further, the minerals were studied Shazly & Saleeb 1972).