Azurite

Also known as Blue Malachite, Azurite is a smaller-scale source of metallic copper. It is also used in jewelry and as an ornamental stone. Until the Middle Ages, Azurite was pulverized and used in the preparation of pigments called "mountain blue" and "Armenian stone". These were widely used by painters until it was discovered that the color produced was not stable. Azurite powder, after a long period, absorbed moisture from the air and turned into another mineral, malachite, which is green. Although pure Azurite is very soft, it is often cut for jewelry making. Azurite results from transformations in preexisting minerals, therefore it is considered a secondary mineral. It forms in the oxidized zones of copper deposits that have been altered by being exposed to air and water. Placed in hydrochloric or nitric acid, Azurite dissolves with an effervescent hiss. It melts easily if held over a flame and turns black when heated.