Barite (barium sulphate)
Color: brown, yellow-brown, colorless, blue, red or green.
Moh’s hardness: 3
Refractive index: 1.63
Critical angle: 38°
Specific gravity: 4.3-5
Cleavage: Cleaves easily in 2 directions.
Fracture: Brittle, uneven.
Heat sensitivity: Very high.
Pleochroism: Blue – weak dichroism.
Birefringence (double refraction): Medium (.012)
Crystal structure: Orthorhombic
Cutting: Due to extreme brittleness and cleavage problems, even performing must be done on an extremely fine lap.
Polishing: Wax lap with alumina. Scratch-free facets may not be obtainable.