Here are some extremely sharp, twinned crystals of shiny cassiterite sitting on a bed of cleavelandite (albite) with muscovite mica. The surface of this specimen is from the pocket lining of a vug in a pegmatite formation in a mine in Brazil. The cassiterite has formed in sharp twinned crystals with a brilliant metallic luster which catches and reflects the light. These crystals are colored a brownish black, and are unusually sharp and well formed - much better than many cassiterite crystals from hydrothermal vein structures.