TrekGEO > Mineral Trail > Kanto region > Saitama pref. > Yoshimi-Hyakuana

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Yoshimi city, Hiki county, Saitama pref., Japan


Salt weathering

Sulfate minerals growing on the surface of the rhyolitic tuff of the Hatakeyama Tuff Member of the middle Miocene (15 Ma) Arakawa Formation. 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.


Outcrop of the Hatakeyama Tuff Member of the Arakawa Formation. The reniform group of white alunogen is on the surface of rhyolitic tuff. The gray basement at the upper left is tuff. White bubbly structure on the surface is aggregate of sulfate minerals such as alunogen. Sulfate minerals crystallized when dissolving water in tuff evaporated in a dry climate.

Reported Minerals

  • Alunogen
  • Gypsum
  • Alum
  • Jarosite
  • Thenardite
  • Epsomite
  • Halotrichite
  • Tamarugite
  • Hexahydrite

Mineral Assemblages

  • Alunogen - Alum - Jarosite - Thenardite
  • Hexahydrite


Related Occurrences

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