Native gold and platinum-iron alloy. Kalimantan, Indonesia
This is the same field of view as previous section but after removal of the carbon-coating (it is rotated by 90°). Many gold grains (yellow) have porous gold enrichment rims (top left) and some show white-yellow higher reflectance cores and yellow lower reflectance rims (centre left). The cores have a lower fineness than their margins which are 980 fine. The platinum-iron alloy is white with high reflectance. A single grain of quartz (dark grey, centre) is coarser grained than euhedral to subhedral zircon (grey) and has a lower reflectance. Black areas are polishing pits.
Grain mount, plane polarized light, x 22, air