Azurite

Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It also known as Chessylite after the type locality at Chessy-les-Mines near Lyon, France. The mineral, a carbonate, known since ancient times, and mentioned in Pliny the Elder’s Natural History under the Greek name kuanos (“deep blue,” root of English cyan) and the Latin name caeruleum.

Crystals are monoclinic, and when large enough to see they appear as dark blue prismatic crystals. Specimens are typically massive to nodular, and are often stalactitic in form. Specimens tend to lighten in color over time due to weathering of the specimen surface into malachite.

Azurite is soft, with a Mohs hardness of only 3.5 to 4. The specific gravity of azurite is 3.77.