Azurite

Formed by the weathering of copper minerals, azurite's brilliant blue colour occurs because of the content of water in this stone.

Sometimes found mingled with malachite which gives a mottled blue/green stone and is often mistaken for lapis lazuli because of its colour, azurite was once ground down to form a paint pigment during the Renaissance.

Used as copper ore in Arizona and South Australia because it contains over 50% copper.