GEYSERITE
Geyserite is the name given to siliceous or calcareous
mineral deposits at & in the vicinity of hot springs and geysers.
Such mineral deposits are typically composed of opaline silica (SiO2ánH2O),
but sometimes they are calcareous, resulting in a surficial travertine
deposit (e.g., Mammoth
Hot Springs, Wyoming). Siliceous geyserite is also known as siliceous
sinter. It tends to be porous, lightweight, and somewhat
friable. The hydrous silica forms by precipitation from the hot waters
emerging from hot spring or geyser vents.
Geyserite from the Yellowstone Hotspot, northwestern Wyoming, USA (public
display, Field Museum of Natural History, Chicago, Illinois, USA).