Calcite

Although over 70 carbonate mineral species are known, three of them, calcite, dolomite, and siderite, account for most of the carbonate material in Earth's crust.

Calcite is the most common form of calcium carbonate and is known for the great variety and beautiful development of its crystals. It perfectly demonstrates the optical property of double refraction: light passing through is split into two components, giving a double image of any object viewed through it, Its pure form it is colorless, pale-colored, or shite , but it is found in virtually all colors, including blue and black.