AZURITE or CHESSYLITE, a basic copper carbonate Its vivid blue colour contrasts strikingly with the emerald-green malachite, which usually accompanies it. It was known to Pliny as caeruleum. The name chessylite is taken from Chessy, near Lyon, where many fine crystals belonging to the monoclinic system have been found. Hardness sp. gr. Azurite occurs with malachite in the oxidized portions of cop per lodes, being due to alteration of copper sulphides by mete oric waters. It is often formed also by reaction between copper bearing solutions and limestone. It is a common mineral in nearly all copper mines.