Celadonite

Formula: KMgFe3+Si4O10(OH)2 phyllosilicate (sheet silicate), mica group
Specific gravity: 2.95 to 3.05
Hardness: 2
Streak: Greenish white
Colour: Blue-green, olive green, apple green
Environments:

Metamorphic environments
Basaltic cavities

Celadonite occurs as vesicle lining and coatings in altered volcanic rocks of intermediate to basic compositions, under low grade metamorphism.
Common impurities: Mn,Ca,Na