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. 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}"]