Chalcopyrite, pyrite and sphalerite. Neves-Corvo, Portugal
Poorly crystalline collomorphic pyrite (brown-yellow, centre) is intergrown with well crystalline pyrite (light yellow-white, left) and both are extensively replaced by chalcopyrite (yellow), which is intergrown with sphalerite (light grey, bottom centre). The variations in reflectance and body colour of the pyrite are due to differences in grain size and degree of chalcopyrite replacement. The fine-grained pyrite has been replaced more extensively than coarse-grained pyrite, and hence has a lower reflectance.
Polished block, plane polarized light, x 80, air