Mineral stability diagram showing minerals that are stable under changing temperature and dissolved silica concentrations at and just beneath the floor of Yellowstone Lake

Mineral stability diagram showing minerals that are stable under changing temperature and dissolved silica concentrations that are found at and just beneath the floor of Yellowstone Lake.  Two important points illustrated by this diagram are: (1) the minerals that are stable when reacted with vapor-dominated fluids (kaolinite, boehmite) differ substantially from those that are stable when reacted with alkaline-chloride fluids (quartz, chlorite, smectite), and (2) pre-explosion alteration by alkaline-chloride fluids occurs in a temperature range from 125–300° C (257–572° F)and at silica concentrations higher than those in the vapor-dominated systems.