Cassiterite | |
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General | |
Category | Oxide minerals |
Formula (repeating unit) | SnO2 |
IMA symbol | Cst[1] |
Strunz classification | 4.DB.05 |
Crystal system | Tetragonal |
Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
Space group | P42/mnm |
Unit cell | a = 4.7382(4) Å, c = 3.1871(1) Å; Z = 2 |
Identification | |
Color | Black, brownish black, reddish brown, brown, red, yellow, gray, white; rarely colorless |
Crystal habit | Pyramidic, prismatic, radially fibrous botryoidal crusts and concretionary masses; coarse to fine granular, massive |
Twinning | Very common on {011}, as contact and penetration twins, geniculated; lamellar |
Cleavage | {100} imperfect, {110} indistinct; partings on {111} or {011} |
Fracture | Subconchoidal to uneven |
Tenacity | Brittle |
Mohs scale hardness | 6–7 |
Luster | Adamantine to adamantine metallic, splendent; may be greasy on fractures |
Streak | White to brownish |
Diaphaneity | Transparent when light colored, dark material nearly opaque; commonly zoned |
Specific gravity | 6.98–7.1 |
Optical properties | Uniaxial (+) |
Refractive index | nω = 1.990–2.010 nε = 2.093–2.100 |
Birefringence | δ = 0.103 |
Pleochroism | Pleochroic haloes have been observed. Dichroic in yellow, green, red, brown, usually weak, or absent, but strong at times |
Fusibility | infusible |
Solubility | insoluble |
References | [2][3][4][5][6] |
Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains the most important source of tin today.