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Ichino River

Ranzan city, Hiki county, Saitama pref., Japan


Ichinokawa River


Hydrothermal deposit along fault

Chalcedony vein in rhyolitic tuff of the Hatakeyama Tuff Member, the middle Miocene (15 Ma) Arakawa Formation. This chalcedony was possibly formed by low temperature hydrothermal activity associated with the fault between the Arakawa Formation and the Rhoke metamorphic rocks. The Rhoke metamorphic rocks was formed by the Late Cretaceous (100 Ma) low-P metamorphism. The Arakawa Formation is composed of turbidite, alternating beds of mudstone and sandstone, and sedimentary circumstance is bathyal such as continental shelf. The Arakawa Formation conformably overlies the Kozono Formation with basal conglomerate, and conformably underlies the Ichinokawa Formation.

Ichino River

Outcrop of tuff of the Hatakeyama Tuff Member, Arakawa Formation. The white vein at the left of the coin is chalcedony. The grayish-white host is tuff.

Reported Minerals

  • Chalcedony
  • Red Jasper

Mineral Assemblages

  • Chalcedony


  • 1960s: Local people found this locality. Red jasper was mined for ornamental stone.
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