Azurite, It is one of two relatively common basic copper carbonate minerals, the other being bright green malachite.  Azurite crystals are usually dark blue, and often prismatic.  Azurite specimens can be massive to nodular or can occur as drusy crystals lining a cavity.

Azurite is unstable in open air compared to malachite, and often is pseudomorphically replaced by malachite. This weathering process involves the replacement of some of the carbon dioxide (CO2) units with water (H2O), changing the carbonate: hydroxide ratio of azurite from 1:1 to the 1:2 ratio of malachite.

Azurite is found in the same geologic settings as its sister mineral, malachite, though it is usually less abundant. Both minerals occur widely as supergene copper minerals, formed in the oxidized zone of copper ore deposits. Here they are associated with cuprite, native copper, and various iron oxide minerals.

Azurite was known in the pre-classical ancient world. It was used in ancient Egypt as a pigment, obtained from mines in Sinai. Ancient Mesopotamian writers report the use of a special mortar and pestle for grinding it. It was also used in ancient Greece, for example on the Acropolis in Athens. It does not appear to have been used in ancient Roman wall paintings but Roman writers certainly knew about its use as a pigment. The fusing of glass and azurite was developed in ancient Mesopotamia.