Azurite is one of two basic copper carbonate minerals, the other being malachite. Both minerals have intense and vivid colors -- azurite is a deep blue while malachite is a rich green. Azurite and malachite are formed by the weathering process that breaks down copper ore. Malachite represents a later oxidation stage and is thus the more common of the two minerals. Sometimes interesting specimens are found containing both azurite and malachite in the same stone. These are usually referred to as Azure-Malachite.
Azurite has been known since ancient times, and was widely used as a pigment and fabric dye in the middle ages. It bears similarities to lapis lazuli, though they are chemically quite different, since the blue color of lapis derives from lazurite, a sodium silico-aluminate in a sulfur matrix. Azurite can also be confused with sodalite, a chloric sodium aluminum silicate.
Azurite is a fairly soft stone with a hardness of 3.5 to 4 on the Mohs scale. It has a specific gravity of 3.7 to 3.9, so it has similar density to chrysoberyl and garnet. Azurite's refractive index is highly variable, ranging from 1.720 to 1.848.
Today azurite is mainly a collector's stone, highly regarded for its intense color and vitreous luster. It is often used for ornamental objects or cut en cabochon. It it sometimes used in jewelry, but it has a tendency to weather over time -- prolonged exposure to bright light, heat and open air all tend to reduce the intensity of its color over time. It is important not to heat azurite when setting it in jewelry; all mounting of azurite specimens should be done at room temperature.
Azurite is found in many locations in the world. The most famous sources are Utah, Arizona and New Mexico in the USA; Mexico; Namibia, the Congo; Morocco; and Australia. At one time outstanding azurite specimens were found Chessy near Lyon, France; and French azurite sometimes went under the name Chessylite.