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Ilvanite with quartz and limonite Calcium iron silicate Laxey Mine, South Mountain, Owyhee County, Idaho 3016.jpg
Ilvaite (Unknown scale)
Category Sorosilicates
(repeating unit)
Strunz classification 9.BE.07
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/a
Mohs scale hardness 5.5-6
Streak black
Specific gravity 3.8-4.1

Ilvaite is a sorosilicate of iron and calcium with formula: CaFe2+2Fe3+Si2O7O(OH). Both manganese and magnesium substitute in the structure. Ilvaite crystallizes in the monoclinic system in black prismatic crystals and columnar masses. It is black to brownish black to gray and opaque. It has a Mohs hardness of 5.5 to 6 and a specific gravity of 3.8 to 4.1. Ilvaite is structurally related to lawsonite.

It occurs in contact metamorphic rocks and skarn ore deposits. It also occurs less commonly in syenites.

Ilvaite was first described in 1811 on the island of Elba and the name ilvaite from the Latin name ilva of the island. Sometimes referred to as yenite.