Reference work entry
Synonym: Geyserite landscape
This is a type of sinter landscape containing deposits on the ground or hot rock layers derived from the dissolved silica in geysers, boiling springs and hot mineral springs. Siliceous sinter is mainly composed of amorphous opal or chalcedony. The water that brings the dissolved silica to the surface is generally at a temperature over 180 °C. In this respect, siliceous sinter is a good indicator of high subsurface temperatures. Some siliceous sinters contain a small amount of iron or magnesium, which gives them a variety of colours. Dissolved silica is generally in solution in the hot spring water, but if the concentration is very high, some silica will be transformed into the colloidal form when cooled. The process of silica precipitation is complex, and high pH, high saturation, high temperature, and the existence of colloidal silica and other substances promote the formation of opal siliceous sinter. Algae activity can also play a role in this process...
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