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Chert (Sources Dissolved Silica (thermal springs (v. high conc dissolved…

- - - - n.b. amorphous - fine/non crystalline quartz
    - - SiO2 solubility increases substantially
      - Very high temps achieved
      - Siliceous deposits form when water cools to ambient water temp
  - - - Amorphous silica solubility = order of mag higher
    - - Very alkaline conditions possible
      - e.g. East African Rift / lagoons North of Adelaide Mountains, Australia
      - Strong solution of silica
      - Direct silica precipitation if lake dried out i.e. as thin opal crust