Lapis lazuli, also known simply as “lapis,” is a blue metamorphic rock that has been used by people as a gemstone, sculpting material, pigment, and ornamental material for thousands of years. High quality lapis lazuli can be a costly gem. The most desirable specimens have a rich, solid blue color and perhaps a few reflective pieces of gold pyrite.
Unlike most other gem materials, lapis lazuli is not a mineral. Instead, it is a rock composed of multiple minerals. The blue color of lapis lazuli is mainly derived from the presence of lazurite, a blue silicate mineral of the sodalite group with a chemical composition of (Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2.
Lapis Lazuli Gemstones: As a general rule, solid blue lapis or solid blue with a few grains of gold pyrite are the most desirable colors. In the photo above the bottom two cabochons approach that ideal. The large cabochon on the top right has a few thin veins of calcite and some calcite mottling. This stone is attractive and some people might prefer it, but the calcite reduces its desirability for most people. The top left cabochon has large patches of calcite that are intergrown with blue lazurite to yield a faded denim color. It also contains many visible grains of pyrite. For most people, it would be the least desirable stone in the photo; however, some people will enjoy it. Desirability in lapis varies from stone to stone and from person to person.
