Azurite on Dolomite

Azurite is a popular mineral whose name comes from its striking blue color. It is a copper-based mineral that is formed from weathering copper deposits. Azurite is also known as Chessylite, as pristine samples have been found in mines in Chessy, France.

Chemical Composition and Properties

Azurite is a copper carbonate. It has a hardness of 3.5 to 4 and can be easily scratched. Azurite forms tabular or prismatic crystals that are often striated. It has a dull luster and a light blue streak. Azurite often occurs with malachite. Malachite may speckle azurite crystals or may occur side by side with it. Azurite has a conchodial fracture, not fracturing in characteristic planes. It will effervesce in hydrochloric acid and is soluble in ammonia.

History

Azurite was first used as a pigment in Fourth Dynasty Egypt. It was used to make a pigment called Egyptian Blue. In the Middle Ages, azurite was ground, washed and sieved to form a pigment called Prussian Blue. It became the most widely used pigment in Middle Age paintings. Azurite is no longer used as a pigment as it can turn into malachite under certain conditions.

Varieties

Azurite-malachite is a banded variety of azurite which is quite rare. Bluebird azurite is a variety of azurite that is spotted with a dark red mineral called cuprite. Both of these varieties are sought after in the gem trade. In open-air situations, azurite is unstable and loses hydroxyl. This process turns it into malachite while retaining the crystal structure of azurite.

Location

The largest crystals of azurite have been found in Tsumeb, Nambia. Specimens of note are also found in Chessy, France; Black Forest, Germany and Burra Burra, Australia. The best crystals in the United States are found in Arizona, New Mexico, and Utah.

Uses

Prospectors use azurite as an indicator for copper ore. It is popular among collectors, many of whom have specimens on display. Azurite is also carved into beads, cabochons and other ornamental objects. Since light and open air can dull the color of azurite, jewelry makers and collectors will often seal the stone or keep it in a cool, dark place.


Azurite on Dolomite
Touissite Mine, Morocco