Copper, iron and low temperature tin mineralization




Chalcopyrite, pyrite, stannite group mineral, arsenopyrite and covelline. Wheal Jane, Cornwall, Britain


Click hereA single euhedral pyrite (light yellow-white, centre) and subhedral to anhedral arsenopyrite grains (white, higher reflectance than pyrite, bottom centre) are enclosed within chalcopyrite (yellow, left). Chalcopyrite is rimmed by a stannite group mineral (pink-brown, centre), which is inclusion-free, but is also altered to covelline (deep blue, centre right). Quartz is dark grey and well polished (bottom right); chlorite is poorly polished and has lower reflectance than quartz (right centre). Black areas are polishing pits.



Polished block, plane polarized light, x80, air


Chalcocite, bornite and pyrite. Levant Mine, Cornwall, Britain


Click hereChalcocite (blue) has a symplectite-like intergrowth with bornite (brown, centre right). Euhedral to subhedral pyrite (light yellow-white, centre bottom) shows relief against chalcocite and its irregular shape suggests that it has been partially replaced by chalcocite.



Polished block, plane polarized light, x80, air


Bornite, covelline and sulphosalt. Levant Mine, Cornwall, Britain


Click hereBornite (brown, bottom right) is intergrown with covelline (blues) which shows good cleavage, bireflectance and reflection pleochroism. Trace amounts of an uncharacterized sulphosalt (cream-white, bottom right) are intergrown with bornite. Black areas are polishing pits.



Polished block, plane polarized light, x80, air


Haematite. Devon, Britain


Click hereCurved laths of haematite show anisotropy and polysynthetic twinning along (0111) twin planes.



Polished block, partially crossed polars, x 180, air


Cassiterite. Botallack Mine, Cornwall, Britain


Click hereRadiating botryoidal cassiterite, known as wood-tin (light grey-brown), is intergrown with quartz (dark grey, top right). Variations in colour of the cassiterite are related to grain size and abundance of fine-grained silica inclusions.



Polished block, plane polarized light, x 180, air


Cassiterite. Botallack Mine, Cornwall, Britain


Click hereThis is the same field of view as 32e but with crossed polars. Radiating wood-tin showing very strong internal reflections from white (bottom) to dark brown (top) which mask the anisotropy of the cassiterite.



Polished block. crossed polars, x 180, air