Chlorite

Chlorite, a hydrous silicate of magnesium, aluminium, and iron, forming a dark olive-green, nearly opaque, pearly mineral of common occurrence. It crystallises in the hexagonal system in non-elastic laminae, and forms the bulk of the rock chlorite-schist. It fuses with difficulty, but gives off water, and is far softer than hornblende. Hardness = 1.5; specific gravity = 2.6 to 2.8. Chlorite is essentially an alteration-product in rocks of igneous origin.