Danburite (calcium borosilicate)
Color: Colorless, pink, wine-yellow and brownish.
Moh’s hardness: 7
Refractive index: 1.63-1.636
Critical angle: 38°
Specific gravity: 3.0
Fracture: Uneven, conchoidal
Dispersion: Medium (.017)
Heat sensitivity: None
Pleochroism: Weak (pale to lighter color).
Birefringence (double refraction): Weak (.006)
Crystal structure: Orthorhombic
Cutting: Cutting danburite is fairly straightforward.
Polishing: Alumina or diamond on most common polishing laps.