Apatite

 

Color: blue, green, yellow, pink, violet, colorless.

Moh’s Hardness: 5

Refractive Index: 1.632-1.646

Critical Angle: 37.84°

Specific Gravity: 3.17-3.23

Cleavage: Poor, imperfect

Fracture: Conchoidal, brittle

Dispersion: Medium (.013-.016)

Heat Sensitivity: High

Dichroic: Strong to weak depending on the color

Birefringence (double refraction): Weak (.002-.004)

Crystal Structure: Hexagonal

 

Treatments: Blue/green, blue Apatite is usually heat treated to bring out the blue color and to remove silk.