Sulfur “cinder” from Cinder Pool in Norris Geyser Basin, Yellowstone National Park

Sulfur “cinder” attached to a sampling tube that was extracted from Cinder Pool in Norris Geyser Basin.  The “cinder” is sulfur that existed as a molten layer at the bottom of the pool and was carried upward by gas and solidified.  The black color is due to the presence of finely dispersed pyrite.  USGS photo by Jim Ball, 2011, under Yellowstone research permit 5194.