Tetrahedrite-tennantite-bearing copper-silver mineralization

Stromeyerite, bornite, tetrahedrite group mineral and pyrite. Unknown Provenance

Click hereEuhedral pyrite (light yellow-white, top left) and subhedral tetrahedrite (green-grey, centre) are harder than bornite (brown, top) and stromeyerite (pink-grey to blue-grey, bottom right). Stromeyerite shows faint bireflectance and reflection pleochroism from pink-grey (centre right) to blue grey (bottom right). Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

Pyrite, stromeyerite, bornite and tetrahedrite group mineral. Unknown Provenance

Click hereEuhedral to subhedral pyrite (light yellow-white, bottom left) is replaced by copper-silver sulphides and is associated with tetrahedrite (green-grey, centre top). Bornite (brown, centre top) is intergrown with stromeyerite which shows strong reflection pleochroism from blue-lilac (top left) to light purple (centre right). Black areas are polishing pits. Pyrite is scratched (centre left), showing the effect of incomplete polishing at coarser grades leaving relict scratches not removed by later polishing with finer grades of polishing paste.

Polished block, plane polarized light, x 80, air

Stromeyerite, bornite, galena, chalcocite and tetrahedrite group mineral and pyrite. Unknown Provenance

Click hereInclusion-free galena (white, centre right) is intergrown with bornite (brown, top) and stromeyerite, showing purple-grey (left centre) to blue-grey (bottom centre) reflection pleochroism. Stromeyerite occurs in a symplectite-like intergrowth with chalcocite (light blue, centre, bottom right) which is accentuated in the section by relief differences. Subhedral tetrahedrite (green-grey, moderate reflectance, centre left, extreme bottom right) is pitted and is associated with euhedral quartz (dark grey, centre left). Pyrite (light yellow-white, high reflectance, centre) is subhedral to euhedral.

Polished block, plane polarized light, x 80, air

Chalcopyrite, tetrahedrite and pyrite. Ballycummisk, County Cork, Ireland

Click hereChalcopyrite (yellow, centre) is intergrown with silver-bearing tetrahedrite (light grey-green, bottom centre). A single crystal of pyrite (light yellow-white, top centre) is enclosed within chalcopyrite. Dolomite rhombs (medium grey, top right), euhedral quartz (centre left) and chlorite (bottom right) are the gangue phases.

Polished block, plane polarized light, x80, air

Chalcopyrite, tetrahedrite, pyrargyrite and pyrite. Sark's Hope Mine, Sark, Channel Islands, Britain

Click hereAltered euhedral tetrahedrite (light grey, left) is rimmed by chalcopyrite (yellow, centre). Chalcopyrite is zoned with inclusion-rich growth bands (lower reflectance) alternating with inclusion-free bands (centre). Pyrargyrite (blue, centre) has infilled a void between chalcopyrite crystals. Minor amounts of pyrite (pale yellow-white, high reflectance, bottom centre) have altered to limonite (grey) or form small framboids (bottom right, centre top) associated with tetrahedrite. Limonite (grey, top right) pseudomorphs after pyrite occur in chalcopyrite. Quartz is black.

Polished block, plane polarized light. x 180, oil

Galena, chalcopyrite, argentian tetrahedrite, bournonite and native antimony. Le Pulec, Jersey, Channel Islands, Britain

Click hereGalena (white, top) is intergrown with chalcopyrite (yellow, bottom) which carries bournonite inclusions (blue-grey, bottom centre). Argentian tetrahedrite (brown, centre) is rimmed by bournonite (blue-grey, centre right) and chalcopyrite. Small grains of native antimony (white, high reflectance, bottom right) are enclosed within bournonite. Black areas are polishing pits.

Polished block, plane polarized light, x 400, oil