Potsdam SandstoneSandstone in thin section
Thin section of the Potsdam Sandstone shows hematite coatings around the sand grains. In some cases, quartz overgrowth has enlarged rounded grains outlined by the film of hematite. The very fine lines within the grains, also due to hematite, can be explained as evidence for exsolution. When the sandstone was formed, amorphous silica crystallized to quartz, and the iron oxide that was previously dissolved in the amorphous silica formed hematite coatings on the surfaces of sand grains, and within flaws and cracks in sand grains.