Cassiterite

Formula: SnO2 simple oxide, rutile group
Specific gravity: 6.98 to 7.01
Hardness: 6 to 7
Streak: Brownish white, white, greyish
Colour: Black, yellow, brown, red or white.
Solubility: Slightly soluble in hydrochloric and nitric acid; insoluble in sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites
Placer deposits
Hydrothermal environments

Cassiterite is widely distributed. It occurs as a primary mineral in igneous rocks and pegmatites but it is more commonly found as an unaltered primary mineral in hypothermal (high temperature) hydrothermal quartz veins of tin deposits in or near granitic rocks. Because of its durability it is also found frequently in placer deposits.
In high temperature quartz veins associated with granitic intrusions cassiterite is often associated with ferberite, molybdenite and arsenopyrite.
At Llallague, Bolivia, cassiterite in hydrothermal veins crystallises at about 300oC.

Common impurities: Fe,Ta,Nb,Zn,W,Mn,Sc,Ge,In,Ga