sinters

Sinters are mineral deposits formed by the precipitation of minerals from hot, silica- or carbonate-rich waters at or near the surface of a geothermal system. They commonly accumulate around springs, geysers, or along seepage streams, creating crusts, shelves, or terrace-like formations. The deposits are typically layered and can be porous, allowing fossil microbes to be preserved.

Two principal types occur: silica sinter and carbonate sinter. Siliceous sinter consists mainly of microcrystalline silica minerals such as opal or chalcedony and may include microcrystalline quartz. Carbonate sinter consists primarily of calcium carbonate minerals such as calcite or aragonite and is closely related to travertine and tufa deposits. Impurities such as iron oxides or clay minerals impart color.

Formation and textures: as hot waters emerge at or near the surface, cooling and degassing cause minerals to precipitate. Siliceous sinters often form at relatively low temperatures in geothermal fields, producing white to brown crusts and layered terraces; carbonate sinters form around carbonate-rich vents and can create nodular, fibrous, or layered textures. Both types may host microbial mats that influence textures.

Geological and scientific significance: sinters preserve records of past hydrothermal activity and palaeoenvironments, provide insights into microbial life in extreme environments, and are used to study geochemistry and geomicrobiology. They can be sources of silica for industrial use in limited locations, but are primarily of academic interest for their mineralogy and environmental history.