Lapis lazuli, often referred to as just 'lapis', has been used as a gemstone for thousands of years.Lapis lazuli by definition is a rock primarily composed of lazurite (25% to 40%), calcite and pyrite. Lazurite is a feldspathoid silicate and belongs to the sodalite group of minerals. Minor constituents can include augite, diopside, enstatite, mica, hauynite, hornblende and nosean. Lapis lazuli can be easily confused with other blue opaque gems such as azurite and sodalite, but azurite has a lower hardness and is typically darker in color than lapis lazuli; while sodalite in most cases, has a lighter color and its granularity is not as fine as that of lapis lazuli.Although the colour of lapis lazuli is defined by its name, 'the blue stone', its colors can actually range from slightly greenish blue to violetish, medium to dark and from low to highly saturated. The blue is owed to sulfur coloring agents.Lapis lazuli occurs opaque in clarity. Lapis is often included with varying amounts of pyrite and its host rock matrix; calcite. When polished, it can have a vitreous to greasy and sometimes dull luster.