[8] Simple copper carbonate (CuCO3) is not known to exist in nature, due to the high affinity of the Cu2+ ion for the hydroxide anion HO−.

The combination of deep blue color and effervescence when moistened with hydrochloric acid are identifying characteristics of the mineral.

[8][11] The optical properties (color, intensity) of minerals such as azurite and malachite are characteristic of copper(II).

According to crystal field theory, the color results from low energy d-d transitions associated with the d9 metal center.

Azurite is quite stable under ordinary storage conditions, so that specimens retain their deep blue color for long periods of time.

Other notable occurrences are in Utah; Mexico; the Ural and Altai Mountains; Sardinia; Laurion, Greece; Wallaroo, South Australia; Brazil and Broken Hill.

[16] Depending on the degree of fineness to which it was ground, and its basic content of copper carbonate, it gave a wide range of blues.

As chemical analysis of paintings from the Middle Ages improves, azurite is being recognized as a major source of the blues used by medieval painters.

Lapis lazuli (the pigment ultramarine) was chiefly supplied from Afghanistan during the Middle Ages, whereas azurite was a common mineral in Europe at the time.

The notion that specimens must be carefully protected from bright light, heat, and open air to retain their intensity of color over time may be an urban legend.

Paul E. Desautels, former curator of gems and minerals at the Smithsonian Institution, has written that azurite is stable under ordinary storage conditions.

It is usually found in association with the chemically similar malachite, producing a striking color combination of deep blue and bright green that is strongly indicative of the presence of copper ores.