This mineral is naturally birefringent, and magnesium added to this mineral's formula results in (*) dolomite.
Ikaite is an extremely unstable hydrated form of this mineral. Vaterite and aragonite are slightly more stable polymorphs of this mineral, a transparent variety of which is known as Iceland spar. This mineral is naturally birefringent, and magnesium added to this mineral's formula results in (*) dolomite. The primary component of limestone, marble, and marine shells is, for 10 points, what carbonate mineral with a value of three on the Mohs hardness scale and formula CaCO3?
Ikaite is an extremely unstable hydrated form of this mineral.
{calcite} [or {calcium carbonate} before "{carbonate}"]