Azurite Through the Ages: Millennia of Mining Have Not Depleted Its Sources

B. Jones, Rock & Gem, August 2012, pp. 20–24

Azurite, a copper carbonate mineral, is a common secondary mineral. The host is usually a volcanic rock. This collector’s azurite crystals mostly came from Chessy in France (the oldest mine, open since the mid-1800s), Morenci and Bisbee in Arizona, Tsumeb in Namibia, and Touissit in Morocco. The increasing price of copper in the first decade of the 21st century led to the reopening of old known copper mines. Well-crystallised azurite specimens have recently been mined in China, Morocco and Mexico.
           
The quality of well-crystallised samples from a decade-old Milpillas mine in Mexico could be compared to this collector’s samples. Azurite crystals (e.g. the Electric Blue from the Milpillas mine) show dark blue colour with high lustre, and are usually 1–2 inches long prisms or blocky crystals of up to 4 inches in length. They have gradually pseudomorphed into malachite in a highly oxidising environment. Thus, malachite is found more abundantly than azurite. Sometimes, a thin layer of azurite can be deposited atop malachite as the final layer. The light to dark green malachite pseudomorphs from the Milpillas mine are mostly blocky crystals, and range from one to ten inches in size. The Milpillas mine also produced emerald-green bronchantites, a hydrous copper sulphate, of one to two inches long needle-like crystals on a rhyolite matrix. Free copper ions of bronchantite absorb all wave lengths except green, causing its bright green colour.

Abstracted by Kyaw Soe Moe