Ilvaite

Ilvaite is a sorosilicate of iron and calcium. 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. This stone is structurally related to lawsonite.

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

This mineral 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.