Comparison of sulfur "cinders" from two different hot springs in Yellowstone National Park

A comparison of black cinders from Cinder Pool, in Norris Geyser Basin (left), with yellow cinders from an unnamed pool in the West Nymph Creek thermal area (right).  The Cinder Pool cinders are black due to finely dispersed pyrite, whereas the yellow color of cinders from the West Nymph Creek pool is due to the lack of pyrite.  USGS photos by Blaine McCleskey in 2005 (left) and 2004 (right) under permit Yellowstone research permit 5194.