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Ilvaite
Chemical Formula	Ca(Fe2+)2Fe3+[O|OH|Si2O7]
Species	Silicates
Crystal System	Orthorhombic
Mohs Scale	5-6
Specific Gravity	3.8-4.1
Color	Iron-black, dark grayish black
Streak	black
Luster	Sub-Metallic
Refractive Index	n = 1.727 n = 1.870 n = 1.883
Diaphaneity	Opaque
Cleavage	Distinct/GoodDistinct on
Fracture	Irregular/Uneven
Crystal Habit：Prismatic, columnar, radiating, compact massive,
Geological Setting：Contact metasomatic rocks and iron deposits.

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 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