Scheelite (calcium tungstate)
Color: Colorless, yellow, orange, brown.
Moh’s hardness: 4.5-5
Refractive index: 1.918-1.934
Critical angle: 31.5°
Specific gravity: 5.1-6.12
Cleavage: Perfect in 2 directions.
Fracture: Conchoidal, splintery, brittle.
Dispersion: Moderately high (.026)
Heat sensitivity: Low
Pleochroism: Dichroic – Yellow: definite (yellow to brown or orange); colorless has no pleochroism.
Birefringence (double refraction): Medium (.014-.016)
Crystal structure: Tetragonal
Cutting: Cleavage is not too touchy, but be gentle with the stone.
Polishing: Use a tin/lead lap with alumina or a chrome oxide Ultralap. A perfect polish may be difficult to obtain.