Azurite is a deep blue copper mineral produced by weathering of copper ore deposits. The mineral has been known since ancient times, and was mentioned in Pliny the Elder's Natural History. Azurite was sacred to the Egyptians who believed it was an aid to spiritual communication.
Azurite was used as a blue pigment for centuries. Chemical analysis of paintings from the Middle Ages recognizes azurite as a major source of the blues used by medieval painters. True lapis lazuli was supplied from Afghanistan during the Middle Ages but azurite was a common mineral in Europe at the time.
Pictured: Velvet Beauty. It was found in 1890 at Bisbee, Arizona. It weighs about 3 pounds and is about 9" in diameter. For sale at the 2007 Tucson Gem & Mineral Show: asking price, US$25,000