Azurite (blue) and malachite (green) are both copper carbonates and frequently occur together, either as crystals or in massive layers. Both minerals are created by the oxidation of copper ores, and occur in the so-called oxidation zone of copper deposits. There are many localities for both minerals, but one of the best known is Bisbee, Arizona. In this old copper mine azurite and malachite are intergrown and also form crystals and nodules, and sometimes in masses that are many feet in diameter.