Azurite :

Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It is also known as Chessylite after the Chessy-les-Mines near Lyon, France, where striking specimens have been found.
 

Azurite crystals are monoclinic, and when large enough to be seen they appear as dark blue prismatic crystals. Azurite specimens are typically massive to nodular, and are often stalactitic in form. Specimens tend to lighten in color over time due to weathering of the specimen surface into malachite. Azurite is soft, with a Mohs hardness of only 3.5 to 4.The specific gravity of azurite is 3.77 to 3.89.