Lapis Lazuli Buying Guide
Lapis lazuli is one of the oldest of all gems, with a history stretching back some 7000 years or more. This mineral is important not just as a gem, but also as a pigment, for ultramarine is produced from crushed lapis lazuli (this is why old paintings using ultramarine for their blue pigments never fade).
For lapis lazuli, the finest color will be an even, intense blue, lightly dusted with small flecks of golden pyrite. There should be no white calcite veins visible to the naked eye and the pyrite should be small in size. This is because the inclusion of pyrite often produces discoloration at the edges which is not so attractive. Stones which contain too much calcite or pyrite are not as valuable.
Lapis lazuli is essentially opaque to the naked eye. However, fine stones should possess no cracks which might lower durability.
Lapis lazuli is cut similar to other ornamental stones. Cabochons are common, as are flat polished slabs and beads. Carvings and figurines are also common.
Lapis lazuli is not an expensive stone, but truly fine material is still rare. Lower grades may sell for less than $1 per carat, while the superfine material may reach $100–150/ct. or more at retail.
Lapis lazuli may occur in multi-kilogram sized pieces, but top-grade lapis of even 10–20 carats cut is rare.
The name lapis means stone. Lazuli is derived from the Persian lazhward, meaning blue. This is also the root of our word, azure.
The original locality for lapis lazuli is the Sar-e-Sang deposit in Afghanistan’s remote Badakhshan district. This mine is one of the oldest in the world, producing continuously for over 7000 years. While other deposits of lapis are known, none are of importance when compared with Afghanistan. Lapis lazuli is also found in Chile, where the material is heavily mottled with calcite. Small amounts are also mined in Colorado, near Lake Baikal in Siberia, and in Burma’s Mogok Stone Tract.
The most common enhancement for lapis lazuli is dying (staining), where a stone with white calcite inclusions is stained blue to improve the color. Other enhancements commonly seen are waxing and resin impregnations, again, to improve color. The color of stained lapis is unstable and will fade with time. As with all precious stones, it is a good practice to have any major purchases tested by a reputable gem lab, such as the GIA orAGTA, to determine if a gem is enhanced.
Sintered synthetic blue spinel was once used as an imitation of lapis lazuli, but is rarely seen today. So-called synthetic lapis lazuli (such as the Gilson product) is more properly termed an imitation, since it does not match exactly the structure and properties of the natural. It is found in various forms, complete with pyrite specks (but all lacking calcite). Various forms of glass and plastic are also commonly seen as lapis imitations.
Properties of Lapis Lazuli
|Composition||Rock made primarily of lazurite (Na, Ca)8(Al, Si)12O24(S, SO4). Also contains haüyne, sodalite and nosean, which are all members of the sodalite group.|
|Hardness (Mohs)||Variable. Generally 5–6|
|Specific Gravity||Variable. Generally 2.7–2.9|
|Refractive Index||ca. 1.50|
|Crystal System||None (lapis is a rock). Lazurite, the main constituent, is isometric, and frequently occurs as dodecahedra.|
Blue, mottled with white calcite and brassy pyrite
|Handling||Due to its softness, care must be taken in the wearing of lapis lazuli.|
|Enhancements||Frequently dyed or impregnated|