any of a group of variously colored, hard, hexagonal calcium minerals, Ca(PO, CO) (F,OH,Cl), found mainly in sedimentary rocks, esp. phosphate rock, and in teeth and bones
See apatite in American Heritage Dictionary 4
(ăpˈə-tītˌ)
noun
A natural, variously colored calcium fluoride phosphate, Ca5F(PO4)3, with chlorine, hydroxyl, or carbonate sometimes replacing the fluoride. It is a source of phosphorus for plants and is used in the manufacture of fertilizers.