Mineral: Galena, Pyrite, Quartz
Chemistry: PbS
Size: 45 mm
Owner: Malcolm Southwood
Photographer: Malcolm Southwood

Steel-grey crystals of galena (to 15 mm), associated with colourless-white crystals of quartz (to 8 mm). The matrix comprises mainly anhedral (massive) galena, with a sprinkling of sub-mm pyrite crystals. 

The galena crystals are twinned on {111}, the so-called "spinel" law. Note also the striations visible on the main face of the large crystal.  These striations are charcteristic of Tsumeb galena crystals and are probably due to lamellar twinning on undetermined lattice planes which may result from mechanical deformation (see Ramdohr, 1980).