Crystals are trigonal-rhombohedral and usually white or colorless.
Crystals are trigonal-rhombohedral and usually white or colorless. It is harder than gypsum but softer than fluorite, placing it as number 3 on Moh‘s scale. Stalagmites and stalactites are often made from this, a common component of  limestone and the primary mineral in metamorphic marble. Shells of many marine organisms are made from this  carbonate mineral. FTP, name this most stable polymorph of calcium carbonate.
Crystals are trigonal-rhombohedral and usually white or colorless.
{calcite} (prompt on calcium carbonate early)