Azurite

Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It is famous for its stunning azure blue color, which has been used as a pigment for centuries. It is often found in nature closely associated with malachite (the green copper carbonate), often forming beautiful 'azure-malachite' specimens with concentric rings of blue and green.

Formation & Geology

Azurite is a secondary mineral that forms in the oxidized zones of copper deposits. It occurs when carbonated waters act upon copper ores. Over time, azurite is unstable in open air and often weather-changes (pseudomorphs) into malachite. This is why many azurite crystals have a green coating or are entirely replaced by malachite while keeping the original azurite crystal shape.

Physical Characteristics

Azurite is relatively soft, with a Mohs hardness of only 3.5 to 4. It has a vitreous to dull luster and a light blue streak. Its most identifying feature is its intense blue color and the fact that it will effervesce (fizz) when in contact with dilute hydrochloric acid, due to its carbonate composition.

Historical Significance

In ancient Egypt, azurite was ground into a pigment and used in wall paintings and eye makeup. Throughout the Middle Ages and the Renaissance, it was the most important blue pigment used in European painting (often called 'mountain blue'). It was also used by the Maya and other Mesoamerican cultures. Today, it is a highly prized mineral among collectors for its deep, rich color.

Pigment of the Ages

Before synthetic pigments were invented, azurite was the primary source of blue in European painting during the Middle Ages and Renaissance. It was ground into a powder to make the pigment "Mountain Blue." However, over centuries, moisture causes azurite to slowly convert into malachite (green). This is why the skies in some very old paintings now look greenish rather than blue.