Lapis lazuli is a rock, no.: 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 composed of sodium, aluminium, silicon, oxygen, sulfur, and chloride. 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.
