Apatite minerals have been synthesized naturally for 2 billion years. They vary in structural form and are either white, yellow, green, blue, purple, gray, red, pink, or multicolored. Typically, the crystals are hexagonal bipyramidal in shape and have a chemical formula of Ca5(PO4)3X (the X being hydroxide, fluorine, or chlorine). The crystals are brittle and have an opaque finish.