Callan Bentley and Robin Rohrback-Schiavone have gigapanned two more sand samples: pyrite sand and actinolite sand. Thanks!
The first one contains pyrite and silicate grains from Cyprus. The second one is from Ontario, Canada. I have already written about this sample: Actinolite sand from Ontario.
I also have to make a small correction. The sand sample with pyrite contains more than just pyrite and goethite. It seems to me that I made a mistake when packing these sands and sent the wrong sample. They are from the same place but with somewhat different composition. The other one I planned to send contained beautiful pyrite cubes, some of them with goethitic/limonitic cover but in this gigapan you also see green silicate grains. I am not sure but they could be epidote grains.
I also recommend to check a gigapan of olivine sand. There are lots of very beautiful bright green olivine grains.