Steacyite

steacyite

nenadkevichite

arfvedsonite

catapleiite

Images

Formula: K_0.3(Na,Ca)₂ThSi₈O₂₀
Cyclosilicate (ring silicate), steacyite group, thallium-bearing mineral
Crystal System: Tetragonal
Specific gravity: 2.95 measured, 3.32 calculated
Hardness: 5
Streak: White
Colour: Gray, dark brown, green, beige
Common impurities: As,Mn,Pb,F,P
Strongly RADIOACTIVE, emits α and β particles, but not γ radiation
Environments

Pegmatites

Localities

At the type locality, the Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada, steacyite occurs as elongated crystals to 2 mm long in cavities in pegmatite veins in nepheline syenite in an intrusive alkalic gabbro-syenite complex. Associated minerals include nenadkevichite, analcime and aegirine (HOM, Mindat).

At Rouma Island, Los Archipelago, Conakry Region, Guinea, steacyite occurs in a miarolitic cavity in nepheline syenite associated with arfvedsonite, astrophyllite, catapleiite, eudialyte, serandite and villiaumite (HOM, Mindat).

At the Dara-i-Pioz Massif, Districts of Republican Subordination, Tajikistan steacyite occurs in quartz - albite - aegirine veinlets and in albitites in syenites. Associated minerals include baratovite, miserite and titanite (HOM, Mindat).

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