oC at a rapid pace and are progressively sheathed or replaced by amorphous silica, building large 3-D fan-shaped structures. Siliceous microstromatolites at Rotokawa, located in the outwash from hot springs (60 – 85 o C), grow at a much slower rate maintaining a level just above the water surface. Growth is initiated on protruding pumice stones and wood fragments. At Champagne Pool, Waiotapu, siliceous microstromatolites grow on native sulphur accumulated around the pool edge or on protruding parts of the pool bottom. Their rate of growth (0.02 – 0.03 mm day -1 ) and size is greater than at Rotokawa. Orange precipitates in the pool, previously identified as flocculated antimony rich sulphides and sulphur, appear to be entirely biomediated. It is not known whether the bacteria are actively metabolising sulphur or antimony or whether biomineralization is passive. These biomineralization effects strongly increase surface areas for potential metal – mineral – microbe interactions and thus effect metal distributions in sinter deposits.
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