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

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

Abstracted by Kyaw Soe Moe