When they occur, crystals are acicular or prismatic, and ofter twinned. More usual habits are stalactitic, botryoidal masses with a fibrous, banded structure, and crusts. Malachite is a rich green and has a pale green streak. It is translucent to opaque, and it has a vitreous to adamantine luster on crystal face; fibrous habits have a silky luster.
*Formation: Forms in the oxidized regions of copper deposits, often with secondary minerals, including lazurite.
*Tests: It is soluble in dilute hydrochloric acid, with effervescence.