Pitchstone Plateau, Yellowstone, rhyolite with sanidine
Pitchstone Plateau, Yellowstone, rhyolite with sanidine(Left) Sample of the Pitchstone Plateau rhyolite flow, which erupted about 72,000 years ago, making it is the youngest rhyolite at Yellowstone. The blocky white crystals in this sample are the mineral sanidine, whereas the rounded crystals are quartz.