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Siliceous sinter

Chemical Process (Liquid-phase growth) - Ground surface

Required Geological Setting

Island arc volcanoes


A kind of hot spring sinters composed of amorphous silicic acid or opal deposited from hot spring water. Silicic acid dissolved in hot spring water deposits as amorphous silicic acid, [SiOx(OH)4-2x]n, by water temperature lowering or pH increasing. Silicic acid can deposit stably in the wide pH range between 1.0-10.0, and pure white silicic acid (siliceous sinter) deposits from acidic hot spring water with a pH less than 1.0. Silicic acid deposits with amorphous iron oxides in the pH range between 3.0-7.0 from iron containing hot spring water, and colored silicic acid such as Tsugaru-Nishiki-ishi is formed. These silicic acid changes to jade or agate during diagenesis. Some locations produce transparent globular aggregates of siliceous sinter.

Siliceous sinter

Distribution of siliceous sinter described in this site. Deposits align along continent-side (Eastern side) of the volcanic front. The yellow line is the volcanic front.

Reported Minerals

  • Siliceous sinter


  • Jakotsu River (Siliceous sinter)
  • Atami Hot Spring (Siliceous sinter)

Related Occurrences

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