Ilvaite

sorosilicate

hedenbergite

Formula: CaFeFe2+2O(Si2O7)(OH)
Sorosilicate, lawsonite group
Specific gravity: 3.99 to 4.05
Hardness: 5½ to 6
Streak: Black, inclining to green or brown
Colour: Iron-black, dark grayish black
Solubility: Gelatinises with hydrochloric acid
Environments:

Plutonic igneous environments
Metamorphic environments
Hydrothermal environments

Ilvaite is a rare sorosilicate primarily found in iron-rich metamorphosed limestone and dolostone or zinc and copper deposits; less commonly it is found as a minor mineral in mafic and ultramafic rocks either as a late-stage primary mineral or as the result of hydrothermal alteration (Mines & Minerals 25.39). It also occurs in sodalite-syenite and in zeolites (Webmin, Dana). Associated minerals include quartz, magnetite, hedenbergite, sphalerite and fluorite (HOM).

At Fengjiashan, Hubei, China, ilvaite occurs on quartz or calcite (MinRec 38.1.37).

At Whin Sill, Teesdale, England, ilvaite has been found in mafic-pegmatite veinlets, associated with ilmenite, titanite and apatite. The ilmenite may form pseudomorphs after titaniferous magnetite. The ilvaite encloses small grains of zircon, rutile, pyrrhotite, chalcopyrite and sphalerite (Mines & Minerals 25.39).

In the Deccan traps of India, ilvaite is found only in the basalt of the Kurar quarry, Bombay-Malad, growing on quartz and second-generation calcite, but even there it is infrequent. It is associated with quartz, calcite, hematite, pumpellyite and rarely andradite, but never with babingtonite or julgoldite (MinRec 34.1.50).

At the type locality, Torre di Rio - Santa Filomena area, Elba Island, Italy, ilvaite occurs as aggregates with pyroxene and dolomite (Dana).

At the Los Remedios mine, Taxco mining district, Mexico, ilvaite has been found with overgrowths of rhodochrosite and fluorite (MinRec 42.5.430).

Common impurities: Mg,Mn

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