meionite


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meionite

[′mī·ə‚nīt]
(mineralogy)
3CaAl2Si2O8·CaCO3 A scapolite mineral composed of calcium aluminosilicate and calcium carbonate; it is isomorphous with marialite.
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3 mm on a thin overgrowth of albite on a meionite crystal.
3 mm on meionite at locality 48 (see cowlesite description above).
The mineral occurs both as euhedral, pseudotetragonal, bipyramidal, colorless to white, opaque crystals up to 5 mm, and as elongated anhedral growths replacing meionite fibers parallel to the c axis of the meionite.
At locality 30 this mineral was found as translucent white crystals up to 1 mm on altered meionite, microcline and other minerals in a 50 X 20 X 15-cm pocket in a sheared pegmatitic rock in contact with a diopside-carbonate metasediment.
At locality 52 it occurs as fibrous inclusions in phlogopite; at locality 21 it forms inclusions in heulandite-Ca; at locality 5 it appears as inclusions in chabazite-Ca; and at numerous localities it appears as overgrowths on and in cavities in meionite.
Thomsonite occurs at localities 47 and 48 as bright white radiating tufts to 2 mm, porcelain-like growths on meionite exposed in cavities by the dissolution of calcite, or translucent tan spherical growths to 5 mm.
Of these, meionite is perhaps most significant, playing a role somewhat analogous to that of glass in zeolite genesis in volcanic rocks and sediments.
At locality 47 one such void contained meionite partially replaced by albite, titanite partially altered to anatase, and the zeolite paragenesis mesolite [right arrow] stilbite-Ca [right arrow] heulandite-Ca [right arrow] chabazite-Ca [right arrow] thomsonite.