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,[1] in Shortugai, and in other mines in Badakhshan province in northeast Afghanistan.[2] Lapis lazuli artifacts, dated to 7570 BCE, have been found at Bhirrana, which is the oldest site of Indus Valley Civilisation.[3] Lapis was highly valued by the Indus Valley Civilisation (7570–1900 BCE).[3][4][5] Lapis beads have been found at Neolithic burials in Mehrgarh, the Caucasus, and as far away as Mauritania.[6] It was used in the funeral mask of Tutankhamun (1341–1323 BCE).[7] 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.

Quality Factors

Variously described as indigo, royal, midnight, or marine blue, lapis lazuli’s signature hue is slightly greenish blue to violetish blue, medium to dark in tone, and highly saturated. In its most-prized form, lapis lazuli has no visible calcite, although it might contain gold-colored pyrite flecks. If the flecks are small and sprinkled attractively throughout the gem, their presence doesn’t necessarily lower lapis lazuli’s value. The lowest-quality lapis looks dull and green, the result of an excess of pyrite. Lapis with white calcite streaks is less valuable.
Lapis frequently contains varying amounts of whitish calcite matrix—the host rock that surrounds the gem—or flecks or veins of glinting yellow pyrite, or both. The gem can also have a smoothly uniform bodycolor, free of visible pyrite and calcite.

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.

Lapis rough can be very large, so large fashioned stones are more common than with many other gemstones. Larger sizes are also more likely to be carved into art objects, used in designer jewelry, or cut into calibrated sizes.

Identification

Color

Blue. Often with white calcite veining or mottling, and gold grains of pyrite.

Streak

Blue.

Luster

Dull, but polishes to a bright luster.

Diaphaneity

Semi-translucent to opaque.

Cleavage

None, though it may split easily along foliation or calcite veins and layers.

Mohs Hardness

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.

Specific Gravity

2.7 to 2.9 or more depending upon the amount of pyrite

Diagnostic Properties

Blue color, association with pyrite, and hardness.

Uses

Cabochons, beads, carvings, spheres, inlay, and pigments.

Chemical formula

Mixture of minerals

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