Sillénite

sillenite

gehlenite

shattuckite

bismutite

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Formula: Bi₁₂SiO₂₀
Simple oxide, bismuth-bearing mineral
Crystal System: Isometric
Specific gravity: 9.16 measured, 9.18 calculated
Hardness: 1 to 2
Streak: Yellowish to brownish white
Colour: Yellow-green, olive-green, reddish brown
Solubility: Soluble in hydrochloric acid
Common impurities: Al,Fe
Environments:

Pegmatites
Metamorphic environments
Hydrothermal environments

Localities

At Fuka, Okayama prefecture, Japan, the deposit is a high-temperature, boron-containing skarn (R&M 965.395). Sillénite occurs on calcite in a hydrothermal vein in gehlenite-spurrite gneiss (Dana).

At the type locality, Durango, Mexico, sillénite is a secondary mineral formed by the oxidation of bismuth-bearing minerals, associated with bismutite and bismuthinite (Mindat, Webmin, Dana, HOM).

At Munihuaza, Mexico, sillénite is associated with shattuckite, ajoite and mottramite variety duhamelite (HOM).

At Monapo, Mozambique, sillénite occurs in a pegmatite (Dana).

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