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Calcite (calcium carbonate)
Color: Brown, yellow, colorless, orange and red.
Moh’s hardness: 3
Refractive index: 1.48 and 1.65
Critical angle: 42.5° and 37.3°
Specific gravity: 2.71
Cleavage: Perfect in 3 directions.
Fracture: Conchoidal, brittle.
Dispersion: Low or medium, depending on direction (.008 & .017).
Heat sensitivity: High
Birefringence (double refraction): Very strong (.172)
Crystal structure: Hexagonal (trigonal)
Cutting: Very difficult stone to cut because of its cleavages, brittle nature and softness. Orient carefully to avoid cleavage problems.
Polishing: Wax lap with alumina or chrome oxide Ultralap.