Cassiterite
Cassiterite (Tin Oxide) · Mineral Specimen and Collector Mineral
Crystal System
Tetragonal, commonly appearing as short prismatic or bipyramidal crystals with frequent knee-shaped twinning.
Mineral Group
Oxides (Rutile group)
Chemical Formula
SnO2 (often with traces of Fe, Ta, Nb)
Formation Process
High-temperature hydrothermal veins and pegmatites associated with granitic intrusions; also concentrated in alluvial placer deposits (stream tin).
About This Crystal
A heavy, dark specimen featuring sub-metallic to adamantine luster. It displays brownish-black to black coloration with some translucent reddish-brown edges when backlit. The crystal faces are well-defined with distinctive high-relief luster.
Physical Characteristics
Color: Brownish-black; Streak: White to brownish; Cleavage: Imperfect; Fracture: Subconchoidal to uneven; Specific Gravity: 6.8–7.1 (very high); Fluorescence: Generally none.
Optical Properties
Refractive Index: 1.990–2.093; Uniaxial (+); Strong birefringence; High dispersion; Pleochroism is usually weak but present in colored stones.
Hardness & Durability
Origin Region
Cornwall (England), Bolivia, China, and the Erzgebirge region of Germany; typically found in granite pegmatites and hydrothermal veins.
Hardness & Durability
Mohs Hardness: 6.0–7.0; Toughness: Brittle; Stability: Very stable, resistant to weathering and chemical attack.
Care & Maintenance
Clean with warm soapy water and a soft brush. Its high density and durability make it relatively easy to store, but it should be kept away from harder gemstones like sapphire or diamond.
Rarity & Value
Common globally as an ore of tin, but high-quality crystalline specimens for collectors are uncommon. Value is based on crystal perfection, twinning (especially 'elbow' twins), and luster.
Special Characteristics
Extreme density for a non-metallic appearing mineral; characteristic 'knee-shaped' twinning; known as 'stream tin' in water-worn pebble form.
Lore & History
Historically the primary source of tin since antiquity, essential for the production of bronze. Metaphysically, it is traditionally believed to aid in grounding, personal protection, and the manifestation of intellectual power.