Sapphire

Color: Red, blue, orange, pink, yellow, clear, about any color

Moh’s Hardness: 8.5-9

Refractive Index: 1.766-1.774

Critical Angle: 34.62°

Specific Gravity: 3.99-4.01

Cleavage: None

Fracture: Conchoidal

Dispersion: Medium (.013)

Heat Sensitivity: Can be... but is usually not a problem

Dichroism: strong, especially in darker colors

Birefringence (double refraction): Weak (.018)

Crystal structure: Hexagonal, trigonal, dipyramidal

Treatments: Assume about any Sapphire you see has been heated unless otherwise noted from the supplier. Heat treating is used to reduce silk and improve colors and generally considered a standard practice.