Apatite

Mineral group: Phosphate mineral
Chemistry: Ca5(PO4)3 (F,Cl,OH)
Color: Usually green, less often colorless, yellow, blue to violet, pink, brown
Crystal system: Hexagonal
Fracture: Conchoidal to uneven
Mohs Scale hardness: 5
Refractive index: 1.634 - 1.638 (+.012, -.006)
Dispersion: 0,013
Birefringence: .002-.008
Pleochroism Present: Blue stones - strong, blue and yellow to colorless. Other colors are weak to very weak
Streak: White
Specific gravity: 3.16 - 3.22

Other:
The primary use of apatite is in the manufacture of fertilizer - it is a source of phosphorus. It is occasionally used as a gemstone. Good qualitys possible for gemstone use are rare but found in sveral locations around the world.