- a mineral, chiefly a hydrous silicate of calcium and aluminum, commonly in tetragonal crystals and usually of a brown to green color; idocrase.
- a green, brown, or yellow mineral consisting of a hydrated silicate of calcium, magnesium, iron, and aluminium: it occurs as tetragonal crystals in limestones and is used as a gemstone. Formula: Ca 10 (Mg,Fe) 2 Al 4 Si 9 O 34 (OH) 4
