Apatite (Hydroxide)
CA5(PO4)3(OH,F,Cl)Hardness: 5.0
Specific Gravity: 3.1
Characteristics: Usually green, blue or brown; prismatic hexagonal crystals are common; vitreous luster; soluble in most acids; poor cleavage in one direction; common varieties include fluorapatite, chlorapitite, and hydroxyl apatite.
Found in teeth and bones; common in trace amounts in carbonate rocks and many metamorphic rocks.
Some uses of apatite include being a primary source of fluorides used in water fluoridation; can act as a chemical stabilizer of subsurface metal contaminants; and in fertilizers and as jewelry.
(Primary text: Perkins, D. 2002. Mineralogy. Prentice Hall.)