Lapis lazuli Overview
Lapis lazuli, semiprecious stone valued for its deep blue colour. The source of the pigment ultramarine (q.v.), it is not a mineral but a rock coloured by lazurite (see sodalite). In addition to the sodalite minerals in lapis lazuli, small amounts of white calcite and of pyrite crystals are usually present. Diopside, amphibole, feldspar, mica, apatite, titanite (sphene), and zircon may also occur. Because lapis is a rock of varying composition, its physical properties are variable. It usually occurs in crystalline limestones and is a product of contact metamorphism. The most important sources are the mines in Badakhshan, northeastern Afghanistan, and those near Ovalle, Chile, where it is usually pale rather than deep blue. Much of the material that is sold as lapis is an artificially coloured jasper from Germany that shows colourless specks of clear, crystallized quartz and never the goldlike flecks of pyrite that are characteristic of lapis lazuli and have been compared with stars in the sky.
Occurrence and Mining
As early as the 7th millennium BCE, lapis lazuli was mined in the Sar-i Sang mines, in Shortugai, and in other mines in Badakhshan province in northeast Afghanistan. Lapis lazuli artifacts, dated to 7570 BCE, have been found at Bhirrana, which is the oldest site of Indus Valley Civilisation. Lapis was highly valued by the Indus Valley Civilisation (7570–1900 BCE). Lapis beads have been found at Neolithic burials in Mehrgarh, the Caucasus, and as far away as Mauritania. It was used in the funeral mask of Tutankhamun (1341–1323 BCE). By the end of the Middle Ages, lapis lazuli began to be exported to Europe, where it was ground into powder and made into ultramarine, the finest and most expensive of all blue pigments. Ultramarine was used by some of the most important artists of the Renaissance and Baroque, including Masaccio, Perugino, Titian and Vermeer, and was often reserved for the clothing of the central figures of their paintings, especially the Virgin Mary. Ultramarine has also been found in dental tartar of medieval nuns and scribes.
For thousands of years, lapis has been fashioned to show off its rich, dark color. Typically, lapis cutting styles for use in jewelry are cabochons, beads, inlays, and tablets, as well as decorative carvings.
Blue. Often with white calcite veining or mottling, and gold grains of pyrite.
Dull, but polishes to a bright luster.
Semi-translucent to opaque.
None, though it may split easily along foliation or calcite veins and layers.
Varies between the 3 of calcite and the 5 to 5.5 of lazurite. Not well suited for use as a ring stone or in bracelets.
2.7 to 2.9 or more depending upon the amount of pyrite
Blue color, association with pyrite, and hardness.
Cabochons, beads, carvings, spheres, inlay, and pigments.
Mixture of minerals