Cassiterite
Current inventory:  2 gems
 

  
Cassiterite is named from the Greek word kassiteros for tinfor its tin content.

Discovered in 1832;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

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

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.02-40

Nickel-Strunz 10th Ed. ID:

4.DB.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
B : With medium-sized cations; chains of edge-sharing octahedra

Related to:

Rutile Group. Rutile-Cassiterite-Platnerite Series. Isostructural with Rutile.

Members of Group:

Rutile Group: Argutite, Cassiterite, Paratellurite, Plattnerite, Pyrolusite, Rutile, Stishovite, Tripuhyite

Varieties:

Ainalite, Toad's Eye Tin, Wood Tin

Synonyms:

Nadelzinnerz, Needle-tin ore, Sparable tin, Stannum calciforme, Tin Spar, Tinstone

Crystal Data

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 fine granular, massive.

Twinning:

Very common on {011}, as contact and penetration twins, geniculated; lamellar.

Physical Properties

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

Optical Properties

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

Occurances

Geological Setting:

In medium- to high-temperature hydrothermal veins and greisen, in granite, granite pegmatite, rhyolite; rarely in contact metamorphic deposits; in large alluvial placers.

Common Associations:

Arsenopyrite, Bismuth, Fluorite, Lepidolite, Molybdenite, Muscovite, Quartz, Scheelite, Topaz, Tourmaline, Wolframite

Common Impurities:

Fe, Ta, Nb, Zn, W, Mn, Sc, Ge, In, Sc, Ga

Type Locality:

Unknown

Year Discovered:

1832; (known for eons)

View mineral photos:

Cassiterite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

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 colored clean gems are very rare and very impressive. Cassiterite crystals are usually very dark and opaque so gem quality crystals are very rare.

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.
 

  
Cassiterite gems for sale: