Malachite and Azurite are both simple Copper carbonates. Azurite occurs as a secondary mineral in the oxidized zones of copper deposits. Where as Malachite occurs as an alteration product in the oxidized zones of copper deposits. They are chemical twins. The only differences is that Azurite holds less water than Malachite. Azurite and Malachite are often mixed together and make great looking cabochons.