Apatite

Apatite (so-called from the Greek apate, deception, from having been formerly mistaken for emerald), a phosphate of lime with a chloride and fluoride. It is usually green, a translucent variety being known as asparagus-stone. It crystallises in hexagonal prisms, commonly occurring in needles in igneous rocks; and it is five in Von Mohs' scale of hardness. When abundant it is valuable as a source of superphosphate for manure.