Chemical Formula: CaFe2+2Fe3+(Si2O7)O(OH)
Locality: Capo Calamita, on Elba.
Name Origin: Named ilvaite from the Latin name of the island of Elba.
Ilvaite is a sorosilicate of iron and calcium with formula: CaFe2+2Fe3+(Si2O7)O(OH). Both manganese and magnesium substitute in the structure. Ilvaite crystallizes in the orthorhombic 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.
Physical Properties
Cleavage: {010} Distinct, {001} Distinct
Color: Iron black, Dark grayish black.
Density: 3.99 – 4.05, Average = 4.01
Diaphaneity: Opaque
Fracture: Uneven – Flat surfaces (not cleavage) fractured in an uneven pattern.
Hardness: 5.5-6 – Knife Blade-Orthoclase
Luminescence: Non-fluorescent.
Luster: Sub Metallic
Streak: brownish black
Photos :
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