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. Azurite is a copper carbonate. Azurite forms tabular or prismatic crystals that are often striated. 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.