Lapis-Lazuli by Wayne Farley

Lapis-Lazuli (Lapis) is discussed in most books on Gemstones. It is also covered in several web-sites (Ref 1 to 4). This report will attempt to select the best information from each of the above resources, and present lapis data, and pictures of ancient and modern utilization of the material in carvings and jewelry.

From Web-Site: (Ref-1, Mineral-Gallery)

“Lazurite is a popular but generally expensive mineral. Well-formed, deep blue crystals are rare and valuable. It is more commonly found massive and combined with other minerals into a rock called Lapis Lazuli, which is an alternate birthstone for the month of September. 

Lapis lazuli (often simply called lapis) is mostly lazurite but commonly contains pyrite and calcite and some other minerals. The name means "blue rock" and is always a brilliant blue with violet or greenish tints. The rich blue color is due to the sulfur that is inherent in the structure of lazurite. Small crystals of pyrite are always present in lapis and their brassy yellow color is both attractive and diagnostic in distinguishing lapis from its also blue cousin - sodalite rock, which lacks pyrite. The calcite produces white streaks in the lapis and too much calcite will lower the value of the stone. 

Lapis lazuli has been mined for centuries from a locality still in use today in the remote mountain valley called Kokcha, Afghanistan. First mined 6000 years ago, the rock was transported to Egypt and present day Iraq and later to Europe where it was used in jewelry and for ornamental stone. Europeans even ground down the rock into an expensive powdered pigment for paints called "ultramarine". Today ultramarine is manufactured artificially. Although no longer the only source of lapis, Afghanistan still produces the finest quality material. 

Lazurite is a member of the feldspathoid group of minerals. Minerals whose chemistries are close to that of the alkali feldspars but are poor in silica (SiO2) content are called feldspathoids. As a result - or more correctly as a function - of that fact, they are found in silica poor rocks containing other silica poor minerals and no quartz. If quartz were present when the melt was crystallizing, it would react with any feldspathoids and form a feldspar. Localities that have feldspathoids are few. 

The name lazurite is often confused with the bright blue phosphate mineral lazulite. However the two minerals can not be confused with each other identification wise because of lazulite's typical vitreous luster and good crystal habit. The carbonate mineral azurite has a very similar color to lazurite but is associated with the green carbonate mineral malachite and reacts to acids. ”