Lapis Lazuli

Lapis Lazuli, blue rock, used since ancient times for ornamental purposes. Typically occurring in limestones found in Afghanistan and Argentina, lapis lazuli consists of the blue mineral lazurite and small amounts of calcite, sodalite, and pyrite. Small particles of pyrite disseminated through the blue rock give the appearance of gold specks.

Lazurite is a complex of sodium aluminum sulfosilicates and calcium aluminum sulfosilicates. It varies in color from deep azure-blue to greenish-blue, is translucent, and has a vitreous luster. The mineral crystallizes in the cubic system (see Crystal), commonly occurring in compact, rounded masses in limestone that has been metamorphosed by heat. Its hardness ranges from 5 to 5.5 and its specific gravity, or relative density, from 2.4 to 2.45.

Lapis lazuli has been used since ancient times for mosaics and other inlaid work, carved ornaments, vases, and other objects. It is also cut cabochon as a gem. It was formerly ground and used as a pigment called ultramarine but has since been replaced by artificial materials. An imitation of lapis lazuli, obtained by staining cracked quartz, is known as Swiss lapis. The mineral jasper, when stained blue, is called German lapis or blue onyx.