Azurite is a hydrated for  of copper (up to 58% copper), it crystallized in striking blue crystals and often forms in association with green malachite. Formula: Cu₃(CO₃)₂(OH)₂  Colour: Azure blue, blue, light blue, or dark blue; light blue in transmitted light  Lustre: Vitreous Hardness: 3½ – 4  Specific Gravity: 3.77 Crystal System: Monoclinic