Topaz

Color: Blue, colorless, pink, orange, red, champagne, sherry-brown, brown and yellow

Moh’s Hardness: 8

Refractive Index: 1.61-1.638

Critical Angle: 38°

Specific Gravity: 3.53-3.56

Cleavage: Very perfect in one direction

Fracture: Conchoidal, uneven

Dispersion: Medium (.014)

Heat Sensitivity: None

Dichroic: Weak to strong depending on color

Birefringence (double refraction): Weak (.008-.01)

Crystal Structure: Orthorhombic

Treatments: Blue is almost always irradiated and heated, some champagne and root beer colors are too.