Malachite, fibrous, is a copper carbonate hydroxide mineral that is opaque green, it gets it's color from it's copper content.  It often forms in botryoidal, fibrous, or stalagmitic masses, this particular specimen is fibrous.

Azurite reaction with water and carbon dioxide to weather into malachite by the hydroxide ions in azurite being replaced with carbonate ions during transformation, so the green malachite is a more stable form. 

Azurite and Malachite have both been used as gems and pigments for thousands of years, and may have been the first mineral to be smelted for copper, kicking off the bronze age.