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Silvialite, ideally Ca4A16Si6024SO4, is tetragonal, I4/m, Z : 2, with a = 12.160(3), c = 7.560(1) ,~, V = 1117.9(8) ,~3 c.a = (I.6217:1, co : 1.583, c = 1.558 (uniaxial negative) l)m -2.75 g/cm 3, D~l~ 2.769 g/cm 3 and H (Mohs) -5.5. It is transparent and slightly yellow, has a good {100} cleavage, chonchoidal fracture, white streak and a vitreous lustre. It occurs in upper-mantle gamet-granulite xenoliths hosted by olivine nephelinite, from McBride Province, North Queensland, Australia. The empirical formula, derived from electron-microprobe analysis, is (Nal.0rCrystal-structure refinement shows disordered carbonate and sulfate groups along the fourfold axis. Silvialite is a primary cumulate phase precipitated from alkali basalt at 900-1000"C and 8-12 kbar tinder high Jso: and./~. The name silvialite, currently used in literature to describe the sulfate analogue of meionite, was suggested by Brauns (1914).

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Liddicoatite, locally with cores of highly X-vacant e1baite, occurs in the High Grade Dike pegmatite of the Cat Lake-Winnipeg River pegmatite field, in the southwestern margin of Superior Province of the Canadian Shield. The liddicoatite contains substantial proportions of the elbaite and rossmanite components; the most calcic composi tion analyzed corresponds to (Cao.498Nao.395Do.1 07)(Li 1.396All.I22Mn0.414Feo.06S)AI6(Sis.888AlO.1 d030(OH3.516F 0.484)' Liddicoatite is closely associated with Ca-enriched spessartine Sps89Grs9Alm2 containing :0; 0.30 wt.% F, and with poliucite, which is the only one with detectable Ca (0.26 to 0.44 wt.% CaO) among pollucite sampies from � 70 worldwide localities. This mineral assemblage was the last product of primary, near-solidus crystallization in the peg matite, and its Ca-enriched members have no analogs, individually or collectively, in other Li-tourrnaline-bearing pegmatites of the parent pegmatite field or elsewhere. Our observations support neither mobilization of Ca from pre existing pegmatite minerals, nor influx of Ca from host rocks. Preservation of some Ca throughout the crystallization of the apatite-and microlite-poor pegmatite seems to be probable, although the specific mechanism of such process remains to be identified.

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