Arsenopyrite-bearing associations




Arsenopyrite and covelline. Cligga Head, Cornwall, Britain


Click hereCharacteristic rhombic crystals of arsenopyrite (white, high reflectance, centre) occur within quartz (low reflectance, bottom centre) and the main gangue phase, tourmaline, which shows bireflectance (greys, centre). Banded covelline (deep blue, top left) has extensively replaced a large arsenopyrite crystal. Black areas are vugs and polishing pits.



Polished block, plane polarized light, x80, air


Arsenopyrite, covelline, altered sphalerite, stannite and chalcocite. Cligga Head, Cornwall, Britain


Click hereCoarse-grained subhedral to euhedral arsenopyrite (white, high reflectance, right) has been replaced by banded covelline (deep blue, bottom left). Altered sphalerite (bottom centre) shows an anomalous, but characteristic, brown-grey surface colour associated with its replacement by copper-rich minerals. Chalcocite (light blue, centre) has replaced sphalerite about its grain edges and along veinlets. Chalcocite has altered to covelline (deep blue, centre). Minor amounts of stannite (brown-yellow, centre right) surround the altered sphalerite. Quartz (light grey, centre) is the main gangue material.



Polished block, plane polarized light, x80, air


Scheelite, arsenopyrite and chalcopyrite. Portugal


Click hereCoarse-grained scheelite (light grey, left) encloses trace amounts of chalcopyrite (yellow, bottom left). Subhedral arsenopyrite (white, bottom right) is fractured along its (101) cleavage and is altered to scorodite (light grey) which is difficult to distinguish at this magnification. Dark grey area is quartz (top right). Banded grey (centre right) areas are secondary arsenates.



Polished block, plane polarized light, x80, air


Chalcopyrite, arsenopyrite, pyrite, sphalerite and native gold. Clogau Mine, Wales, Britain


Click hereArsenopyrite (white, centre) is highly fractured and these fractures are infilled by sphalerite (light grey, centre left), native gold (yellow-white, high reflectance, poorly polished, centre) and chalcopyrite (yellow). Chalcopyrite also encloses much of the arsenopyrite. A euhedral cube of pyrite (light yellow-white, right centre) has lower reflectance than arsenopyrite. Dark grey area is quartz (bottom). The native gold is 950 fine, and to the eye has a higher reflectance than the photomicrograph would suggest.



Polished block, plane polarized light, x 80, air


Pyrite, arsenopyrite, sphalerite and chalcopyrite. English Lake District, Britain


Click hereEuhedral rhombic arsenopyrite (white, right) has higher reflectance than pyrite (light yellow, bottom left). Sphalerite (light grey) occurs as rare inclusions in arsenopyrite (top right) but mainly as large aggregates (bottom) with abundant crystallographically oriented chalcopyrite inclusions (chalcopyrite disease). Dark grey areas are chlorite-rich gangue.



Polished block, plane polarized light, x 40, air


Pyrite, arsenopyrite, sphalerite, chalcopyrite and galena. English Lake District, Britain


Click hereEuhedral rhombic arsenopyrite (white, high reflectance, centre), showing faint reflection pleochroism (centre right), is enclosed within a fine-grained mosaic of pyrite (light yellow). Sphalerite (light grey, bottom left) has abundant chalcopyrite (yellow) inclusions in its cores but has inclusion-free rims (bottom left). Quartz gangue (top right) is dark grey.



Polished block, plane polarized light, x40, air