Azurite

Azurite is a secondary mineral that forms when carbon-dioxide-bearing waters react with copper ores and redeposit copper in pore spaces, fractures and cavities, usually as massive or nodular material and only rarely as well-formed crystals. Notable sources include Arizona (Bisbee, Morenci), New Mexico and Utah in the United States, Chessy in France (the type locality, hence the old name "chessylite"), Tsumeb in Namibia, Queensland in Australia, Mexico, Morocco, Russia, China and the Democratic Republic of the Congo.

Azurite is recognised by its deep blue colour, light blue streak, low hardness, unusually high specific gravity (3.7 to 3.9) and slight fizzing in dilute hydrochloric acid. It is confused with lapis lazuli and sodalite, but has a higher refractive index and specific gravity, lower hardness and strong birefringence. Azurite slowly alters to green malachite. Natural azurite is rarely treated to change colour, but rough is often stabilised with resin, and much inexpensive "azurite" is reconstructed material: crushed azurite (often with malachite or chrysocolla) in resin or another binder; some sellers call such material "synthetic". Names such as "copper lapis" and "Arctic opal" are misrepresentations.

Azurite is soft, brittle and sensitive to heat; it slowly loses its blue colour and turns green when exposed to air, heat, light and humidity. Clean it only with water, mild soap and a soft brush or cloth; avoid acids, abrasives, ultrasonic and steam cleaners, and do not heat it during jewellery repair. Store it separately from harder stones, in a closed, dark box. It suits occasional wear in protective settings rather than rings or bracelets. Wearing finished pieces poses no known hazard, but azurite dust from cutting is toxic because of its copper content, so cutters should wear masks.

The name comes from the ancient Persian word "lazhward", meaning blue; the French mineralogist François Sulpice Beudant named it azurite in 1824. The ancient Egyptians mined azurite on the Sinai Peninsula and smelted it for copper, and ground azurite was used as a blue pigment from ancient Egypt onward. In Europe it was the most important blue pigment of the Middle Ages and Renaissance, until man-made pigments such as Prussian blue gradually replaced it from the 18th century; in many old paintings the azurite blue has partly turned green as it weathered to malachite.