Chemical composition -- A family of phosphates containing calcium, iron, chlorine, and several other elements in varying quantities. The most common variety contains fluorine, and fluorapatite is the main constituent in bones and teeth!
Color -- very wide color range.
Optics -- R.I 1.60-1.67.
Durability -- Hardness 5. Brittle. Not durable enough for use in rings, but okay for jewelry items not exposed to heavy wear, such as earrings, brooches, or pendants.
Crystal structure -- Hexagonal.
Specific Gravity -- 3.10-3.35.
Sources -- Widely distributed, but Mexico is the major source, especially of yellow apatite. Some 100+ carat stones are known, but most are under 20 carats. Blue and violet stones are the rarest and are usually under 2 carats.