Lapis lazuli (pronounced /ˈlæpɪs ˈlæzjʉlaɪ/ or /ˈlæzjʉli/ LAP-iss LAZ-ew-lye/lee) (sometimes abbreviated to lapis) is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color.
Lapis lazuli has been mined in the Badakhshan province of Afghanistan for over 6,000 years, and trade in the stone is ancient enough for lapis jewelry to have been found at Predynastic Egyptian sites (as archeologists have frequently stated, but lapis could also be found in, e.g., theSiwa Oasis in the Western Libyan desert), and as lapis beads at neolithic burials in Mehrgarh, the Caucasus, and even as far from Afghanistan as Mauritania.
Lapis lazuli is a rock, not a mineral: whereas a mineral has only one constituent, lapis lazuli is formed from more than one mineral.
The main component of lapis lazuli is lazurite (25% to 40%), a feldspathoid silicate mineral with formula: (Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2. Most lapis lazuli also contains calcite (white), sodalite (blue), and pyrite (metallic yellow). Other possible constituents: augite; diopside;enstatite; mica; hauynite; hornblende, and nosean. Some lapis lazuli contains trace amounts of the sulfur-rich löllingite variety geyerite.
Lapis lazuli usually occurs in crystalline marble as a result of contact metamorphism.
The finest color is intense blue, lightly dusted with small flecks of golden pyrite. Stones with no white calcite veins and only small pyrite inclusions are more prized. Patches of pyrite are an important help in identifying the stone as genuine and do not detract from its value. Often, inferior lapis is dyed to improve its color, producing a very dark blue with a noticeable grey cast which may also appear as a milky shade.
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