Cassiterite

Cassiterite is the principal ore of Tin. It has been an important ore of tin for centuries and is still the greatest source of tin today. It has almost twice the dispersive fire of diamond! Lighter coloured clean gems are very rare and very impressive. It also has an extremely high refractive index, which results in exceptional fire and dispersion. Cassiterite crystals are usually very dark and opaque so gem quality crystals are very rare.  The name Cassiterite is derived from the Greek “kassiteros”, meaning tin. Cassiterite is not known to be treated or enhanced in any way.

Current sources of gem quality crystal are Cornwall, England; Otjimbojo, Namibia; Xue Bao Diang Mountains, Sichuan Province, China; Fazenda do Funil, Ferros, Minas Gerais, Brazil; several locations in Bolivia. Bolivia is thought to have the best gem quality deposits and it is one of the few sources for ‘wood tin’. In the late 1990s, both Russia and China produced very largely, high-quality transparent crystals.

Category:  Oxide minerals
Chemical Formula: SnO2
Tin Oxide
Molecular Weight: 150.71 gm
Composition: Tin 78.77 % Sn 100.00 % SnO2
Oxygen 21.23 % O
  100.00 % 100.00 % = TOTAL OXIDE

 

Crystallography: Tetragonal – Ditetragonal Dipyramidal
Crystal Habit: Crystals short to long prismatic {001}, with {110} and {100} well developed, terminated by steep pyramidal forms, to 10 cm; less commonly pyramidal. In radially fibrous botryoidal crusts and concretionary masses; coarse to finely granular, massive.
Twinning: Very common on {011}, as contact and penetration twins, geniculate; lamellar.

 

Cleavage: Perfect on {100}, Indistinct on {110}; partings on {111} or {011}
Fracture: Irregular/Uneven, Subconchoidal
Tenacity: Brittle
Moh’s Hardness: 6.0 – 7.0; Vickers Hardness: VHN200=1239 – 1467 kg/mm2
Density: 6.98 – 7.01 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive

 

Color: Black, Brownish Black, Reddish Brown, Red, Yellow, Gray, White; rarely Colorless
Transparency: Transparent to Translucent
Luster: Adamantine to Vitreous
Refractive Index: 1.990 – 2.101  Uniaxial (+)  (anomalously Biaxial)
Birefringence: 0.0900 – 0.1030
Dispersion: Very high; 0.071 (nearly 2x diamond)
Pleochroism: Strong to Very Weak; Dichroic in Yellow, Green, Red, Brown
Anisotropism: Relatively Strong; Color in reflected light: white to gray; Internal reflections: deep blood red