Classic Cassiterite pseudomorph from Wheal Coates, St. Agnes, Cornwall. Twinned and inter grown crystals of the Feldspar Orthoclase have been completely replaced by granular brown Cassiterite. Crystals of replaced Orthoclase measure to 2.3cm in the Carlsbad twin law. One edge of the crystal group show previous attachment to a white-light brown 'Kaolinite'. A fine specimen of the classic pseudomorph.