T}IE AMERICAN MINERALOGIST, VOL 54, JANUARY-FEBRUARY' 1969

YAGIITE, A NEW - ANALOGUE OF TnnooonoE. BuNcn,Ames Research Center, 1r,4S,4,Mofett Field,,CaliJornio 94035

AND Lours H. Fucns, Argonne National Loboratory, Argonne, Illinois 60139. Assrnacr , a new osumilite-type sodium-magnesium-aiuminum silicate is {ound in silicate inclusions of the Colomero meteorite associated with aluminous titanian , , and . The mineral is colorless, uniaxial positive, and weakly pleochroic; relractive indices are e:1.544, o:1.536. Average composition, de- termined by the electron microprobe, is SiOz61.7; ALOr 19.1; CrrOr 0.1;TiOz 0.8; FeO 2 4; MgO 10.5;MnO 0.2; CaO 01;NarO 3.7 and KzO 14, sum 100.0wt /g. X-ray data show that yagiite is isostructural with osumilite; unit cell dimensions are a:10.09+0.01 it, c:14.20+o.03 A. StrongestX-ray lines are: 3'228 OW),5.059 (65), 3.726 (50). Calculated density is 2.70 g/cm3.

INrnonucrroN Yagiitel, (pronounced'ya-gc-ite), a new osumilite-typemineral with the structural formula (Na, ,o Ko.ao)(Mgz oo) (Mgo oo Feo.r+Tio.ro Alr.so) (Siro.z:Alr.zs) Oro, has been found in silicateinclusions of the Colomera iron meteorite.X-ray powder data indicate that yagiite is very similar to osumilite, and to two other osumilite-type meteorite minerals, roed- derite and merrihueite; there are only minor differencesin line spacings and intensities. The mineral was named for Dr. Kenzo Yagi, Professorof Geology, Hokkaido University, Sapporo,Japan in honor of his contributions to mineralogl' and petrology.

Occurrenceand opt'icalproperties. Yagiite occurs interstitially to small equant grains of aluminous titanian diopside in a small silicate inclusion (0.8 mm in diameter)surrounded by nickel-iron;minor amountsof whit- Iockite, tridymite and plagioclaseare alsopresent. A detaileddescription of the mineralogy and mineral chemistry of the Colomerameteorite is given by Wasserburget al. (1968) and in a paper in preparation by Bunch and oihers. In reflected light yagiite has much lower reflectivity than the co-ex- isting pyroxene, approximately equal to that of plagioclase.fn trans- mitted light it showsf aint pleochroism (e: colorless,c,l: very light blue)

l The name yagiite has been approved by the Commission on New Mineral Names of the International Mineralogical Association. t+ YAGIITD 15

T,tern 1. Soun PnoponrrBsol Y.q.curp,q.Nn RBleroo Osuurr,rrn-TvpB MrNlner-s

Roedderite, Merrihueiteb Osumilite" Yagiite

@(A) 10139+0.01 10.16+0.06 10.17 10.09+0.01 c (A) 14.275+0 01 14.32+006 t+.34 t4 29+0.O3 p, g/cc (meas.) 2.6 2.87 (calc.) 2.64 2.70(calc.) |.537 1.546(avg.) 1.536 e | 542 1.559-1.592 1.550 (avg.) 1.544 e-6 0.005 0.004 0.008 colorless greenishblue dark blue colorless (pleochroic) (pleochroic)

'Fuchs, et aJ. (1966). b Dodd, et al,. (1965). " Miyashiro (1956). and is uniaxial positive. Refractive indices are €:1.544*0.002 and o:1.536*0.002. Optical and physicalproperties of yagiite are compared with those of other osumilite-typeminerals in Table 1.

X-ray data. An X-ray powder pattern of yagiite was obtained using a Norelco powder camera,diameter of 11.45cm with Ni-filtered CuKa1,a2 radiation.The pattern wasindexed on a hexagonalunit cell with a:10.09 +0.01 A and r:14.29+0.03 A. CalculatedX-ray density(Z:2) is2.70 g/cmt. X-ray data for yagiite are compared with those for osumilite, roedderite and merrihueite in Table 2. Yagiite is isostructural with other osumilite-type minerals as indicated by the simifar X-ray powder pat- terns and unit cell parameters.Differences in line spacingsand intensities for yagiite compared to osumilite and roedderite'areminor, but show more marked variations compared to merrihueite.

Chemistry.Analyses were carried out with an ARL-EMX electron micro- probe usingwet-chemically analyzed mineral standardssimilar in compo- sition to yagiite. Correctionswere madefor drift, deadtime,background, mass absorption and fluorescence.No atomic number correctionswere made becauseof standard-samplesimilarity. To minimize volatilization of alkalis during analysesa lolv sample current (0.02 microampere), short counting time (10 seconds)and an acceleratingvoltage of 15 kV were used.Sample grains of the type osumilite (Sakkabira,Japan) were ana- lyzed simultaneouslywith yagiite for comparativepurposes. Results of these analysesalong with published electron microprobe analysesof roedderite and merrihueite are listed in Table 3. It is apparent that yagiite is most similar in composition to osumilite THEODORE D, BUNCH AND LOUIS II . FUCITS

T,s.sr,r2. X-R.qv Pownnn Drpl rcrroN Dnre

Merrihueite Roedderite Osumilite Yagiite Mezo-Mad,a,ras Indarch Sakkabira, Japan Col,omera

r d(L) r d(L) r d(A) d(L)

1010 10 8.827 30 8.827 5 873 0002 80 7.13 50 7.126 70 7.126 30 7.r2 l0t2 10 5.50 10 5.532 60 5.532 15 5.529 lt20 30 5.03 80 5.062 70 5.091 65 5.059 2020 5 4.40 90 4.383 60 4 392 15 4.368 ll22 10 4.13 80 +.t29 80 4.129 20 4.127 2022 100 3.73 90 3.729 80 3.745 50 3.726 0004 5 3.60 80 3.567 60 s.567 25 3.565 1230,10T41 30 3.295 60 3.300 l5 3.299 l23r 90 323 100 3.229 t00 3.225 t00 3.228 r2B2 10 3.01 10 3.006 40 3.006 20 2.990 1124 10 2.940 303-0 60 2.92 90 2.916 90 2.916 40 2.909 2024 loo 2.774 90 2.761 90 2.770 50 2.765 lz6J 30 2.7r7 30 2.721 t0 2.716 2240 60 2.531 40 2 536 15 2.523 2t34,t3401 l0 2.432 20 2.432 5 2.428 1341 10 2 393 40 2.388 5 2.390 1343,1126l 40 2.168 30 2.168 10 2.159 2026,4ti42]l 30 2 099 t0 2.096 5 2.090 10 2.067 10 2.069 1s44,23501 50 2.0r2 50 2.Ot4 30 2.003 4151 40 t.897 10 1.918 10 1.890 2353,1345\ 40 r.852 50 1.853 25 1.846 3086,4r82J

in that it has aluminum as a major component,whereas merrihueite and roedderite are low in aluminum. Yagiite contains more MgO and Na2O, and lessAIzOs, FeO and K2O than osumilite.It shouldbe pointed out that the original wet-chemicalanalysis reported by Miyashiro (1956)is prob- ably in error owing to contaminationby cordieriteor other mineralsthat coexist with osumilite. Electron microprobe analyses of the two other known osumilite occurrences(Obsidian Cliffs, Oregon and Monte Arci, Sardinia) (Bunch and Olsen,in preparation) are very similar to our micro- probe analysis of Sakkabira osumilite and indicate a narrow composition- al range.Osumilite in thesethree known occurrenceshas crystallizedin cavitiesof rhyolitesin associationwith eitherfayalite or ferrohypersthene and at least one iron oxide (hematite or magnetite).fn contrast, yagiite has crystallized in a magnesium-rich environment with aluminous titani- YAGIITE 17

T,tsr-r 3. Er,nctnoN Mrcnopnosn ANelvsrs ol Osulrrr,nr-Tvpr MrNnnels

Yagiite Osumilite Roedderite" Merrihueiteb Colomera Sakkabira,Japan Ind,arch Mezo-Mad.aras

SiOr 61.7 61.6 71.0 61.8 Al2os t9 l 21.4 0.4 0.2 CrzO: 01 <0.02 TiOz 0.8 0.1 ')i I'eO 2.4 8.6 zJ.l MnO 0.2 08

Mso 10.5 J. ' 19.5 4.4 CaO 0.1 0.1 0.3 Naro J. ' 1.0 4.0 2.0 KzO t.4 2.9 3.3 3.8

Total 100.0 r00.2 100.2 96.7

Structural Formulas for Osumilite-Tvoe Minerals

Coordination XII VI Iv IV

Basic Formula" (Alk or Me) Mez Mes (si, ADu Oao Osumilite Sakkabira (K, Na, Ca)o rs (Fe, Mg), oo (Mg, Al, Mn), e5 (Si, Al)1, Oso Yagiite Colomero (Na, K)r -11 Mgr oo (Mg,Fe,Al,Ti)r oo (Si, Al)12 Oao Roedderite' Indarch (Na, K)r nn Mgz oo (Mg, Fe)3 tr Sit, Oro Merrihueiteb Mezo-Madaros (K, Na)1 zz Fe2 6s (Fe. Mg)a zo Sirs Oro

" Fuchs, et al (1966). b Dodd, et al. (1965). " Schreyer and Schairer (1962). an diopside. These environmental differencesare reflected in the relative amounts of MgO and FeO in yagiite and osumilite. Similarly, roedderite, the sodium magnesium analogue of merrihueite, coexists with the mag- nesium-rich minerals enstatite and clinoenstatite (Fuchs et al., 1966), while merrihueite is associatedwith a more iron-rich mineral, "fayalitic olivine" (Dodd et al.1965). On the basis of thirty oxygensper unit cell the analysesin Table 3 can be recast into structural formulas that clearly show the complex solid solution that is possiblefor osumilite-type minerals. At least two substi- tutional pairs (K-Na; Fe-Mg) are possiblefor these minerals, and a com- plete solution seriesprobably exists between the aluminum-poor mem- bers, merrihueite and roedderite, by mutual substitutions of K and Na, 18 THEODOITE ].:, BUNCH AND LOLTIS TI. FUCHS

and Fe and Mg, and from both minerals to the aluminum-rich member osumilite. The basic formula (Table 3) shows that the l2-coordinated positions are occupied by alkalis, but alkalis are not necessarilyessential in forming the structure,as Schreyerand Schairer(1962) have suggested. A further complication is indicated by the possibility that vacancy sites exist in the 12-coordinatedpositions. The formula should contain 2.Oal- kali atoms; osumilite,however, contains only one, yagiite 1.5 and merri- hueite 1.7.In addition, Olsen(1967) has shown that roedderitecan have as many as 0.5 alkali atoms in excessof the empirical formula, and that theseare probably "stuffed" into the structure. The 6-coordinatedposi- tions for yagiite and roedderite are occupiedby magnesium,whereas iron is the predominant cation in this position for osumilite and merrihueite. Both yagiite and osumilite have nearly two atoms of aluminum in the 4-coordinatedsites. Roedderite and merrihueitehave very small amounts of aluminum that can be considerednonessential. We propose that yagiite be restricted to that part of the solid solution regionwith Na> K, Mg) Fe and Si/Al< 7 (atomic ratio) and that osumi- lite be redefinedas that part of the solid solution region with K)Na, Fe)Mg and Si/Al(7 (atomic ratio). This would defi.nethat part of the osumilite-type mineral system involving the substitutions discussed above, with roedderite being the sodium magnesium analogue of merri- hueite, and yagiite the sodium magnesium analogue of osumilite.

AcrNowtnocuuNts

We thank Mr. K. Uetani of the National Science Museum of Tokyo for samples of Sakkabira osumilite. Work by L. H. Fuchs at Argonne National Laboratory was performed under the auspices of the Atomic Energy Commission. One of us (T.E.B.) is supported by an NRC-NASA Resident Research Associateshio.

REI.ERENcES

Dooo, R. T., W. R. VaN Scnuus, axn U. B. M.qnvrx (1965) Merrihueite, a new alkali- ferromagnesian silicate from I)n:eMezii-Modaras chondrite. Science,1491 972-974. Fucrrs, L. H., C. FnoNner,, aNo C. Kr,uN, Jn. (1966) Roedderite, a new mineral from the I ndar ch meteorite. A m er. M iner al'., 5 l, 949-955. Or-snn, E. (1967) A new occurrence of roedderite and its bearing on osumilite-type minerals. A mer. M iner oJ., 52, 1519-1523. Mtvesurto, A. (1956) Osumilite, a new and its . Amer. Mineral,4l, lO4. Scunnvnn, W. nNr J. Scra.rntn (1962) Metastable osumilite- and petalite-type phases in the system MgO-ALOTSiO z. A mer. M i.neraJ., 47, 90. Wassranunc, G. J., H. G. SaNz, nNr A. E. Brxcn (1968) feldspar phenocrysts in the surface of Colomera, an iron meteorite. Science,1671684-687. fuIanuscript receizted.,August 7, 1968; accepted.Jor publication, Ocl'ober1 , 1969.