(i) Orthoclase (clear); (ii) Orthoclase Moonstone; (iii) Rainbow Moonstone respectively.

Moonstone is largely composed of orthoclase which is an important tectosilicate mineral found in igneous rocks and granites. The name is derived from the Greek word meaning “straight fracture,” because its two cleavage planes are at right angles to each other.

Two other names for orthoclase are alkali feldspar and potassium feldspar. The largest documented single crystal of orthoclase measured ~10×10×0.4 m3 and weighed ~100 tons. It was found in Ural Mountains Russia.

Orthoclase is a common raw material for the manufacture of glass, ceramic, porcelain etc.

Some inter growths of orthoclase have an attractive pale luster. They are called as moonstone when used in jewellery. Most moonstones are translucent and white, although grey and peach-coloured varieties also occur. Their luster is called ‘adularescence’ and is creamy or silvery white. Orthoclase is the state gem of Florida.

The gemstone commonly called rainbow moonstone is a colorless form of labradorite. It can be distinguished from true moonstone by its greater transparency and play of color. Orthoclase is one of the ten defining minerals of the on Moh’s scale of mineral hardness.