| Crystal System |
Hexagonal |
| Chemical Comp.. |
Ca5(PO4)3(OH,F,Cl) |
| Color |
Colorless |
| Pleochroism |
None |
| Cleavage |
None |
| Relief |
Low |
| Birefringence |
1st Order Gray |
| 2V | --- |
| Optic Sign | Negative |
| Twinning |
Rare |
Apatite is usually an accessory mineral in igneous and metamorphic rocks. This means it is present as small grains, sometimes as inclusions in other minerals (see below). Apatite can be distinctive because of its six side outline (if cut perpendicular to the c-axis) and low birefringence. If the crystal is large enough, an interference shows that it is uniaxial negative. Bi = Biotite; Ap = Apatite; Plag = Plagioclase
