English: Variation in amorphous silica stability with temperature and dissolved silica activity. Amorphous silica is undersaturated in the region shaded blue and supersaturated in the region shaded yellow. The scatter point and dashed line illustrate how cooling of hot spring water with -2.5 log activity of dissolved silica (~200 mg L-1) can cause amorphous silica to become supersaturated. At the scatter point, the water has a temperature of 80°C. From that point, cooling to about 55°C causes amorphous silica to saturate. Further cooling causes amorphous silica to become increasingly supersaturated. In addition to cooling, other drivers of silica supersaturation in hot spring systems can include evaporation, changes in pH, and other factors (Guidry and Chafetz, 2002). This temperature-activity diagram was calculated with The Geochemist’s Workbench software (Bethke, 2018).