Mercury and antimony sulphides
Stibnite crystals, showing bireflectance and reflection pleochroism (brown-grey to light brown-grey), have altered to stibiconite (dark grey, centre top) along a fracture. Black areas are polishing pits.
Polished thin section, plane polarized light, x80, air
Stibnite showing deformation twins (centre), 'pressure lamellae', and strong bireflectance and reflection pleochroism. Black areas are polishing pits.
Polished block, plane polarized light, x 80, air
This is the same field of view as the previous section but with crossed polars. Stibnite showing strong anisotropy along complex deformation twins and 'pressure lamellae'.
Polished block, plane polarized light, x 80, air
Bladed aggregates of fine-grained cinnabar crystals show characteristic deep red internal reflections. Light coloured internal reflections belong to quartz and carbonates (top right).
Polished block, crossed polars, x 180, oil
Cinnabar and pyrite. Mount Amiata, Italy
Aggregates of cinnabar (blue-grey) showing faint bireflectance and pink-blue to light blue reflection pleochroism (centre bottom) are more common than single subhedral crystals (centre top). Trace amounts of euhedral pyrite (light yellow, high reflectance, centre) occur within cinnabar and the carbonate gangue.
Polished block, plane polarized light, x80, air
Cinnabar (and pyrite). Mount Amiata, Italy
This is the same field of view as 41e but with partially crossed polars. Pyrite is no longer visible. Cinnabar crystals show strong anisotropy (bottom left), but the anisotropy colours are largely masked by strong red internal reflections (centre bottom). The grain size difference between single crystals and aggregates of cinnabar is clearly seen.
Polished block, partially crossed polars, x 80, air