Cassiterite

Chemistry: Tin oxide (tin stone).
Crystal system: Tetragonal; prismatic, capped by pyramids; often twinned (geniculate); massive and granular, botryoidal, reniform with radial fibrous structure.
Color: Transparent to translucent; reddish brown to black, colorless, yellow.
Hardness: 6 - 7
Cleavage: Indistinct: brittle; Fracture: uneven, conchoidal.
Specific gravity: 6.8 – 7.1
Refractive index: 1.997 – 2.093; Uniaxial positive; 0.096.
Luster: Vitreous to adamantine; greasy on fracture.
Dispersion: Very high.
Dichroism: Weak to moderate; yellowish, brownish.
Occurrence: Granite and alluvial, high temperature hydrothermal veins and pegmatites; Australia, Bolivia, Malaysia, Mexico, Namibia, England.

Notes:
Principal ore of Tin; collectors stone; may be confused with diamond, hematite, sphene, zircon; faceted and cabochons.