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Sukumo river

Sukumogawa, Hakone city, Ashigara-Shimo county, Kanagawa pref., Japan



Anorthite phenocrysts in basaltic andesite dike intruded in the Hayakawa Volcanic Breccias erupted from the Hakone Volcano in early Pliocene (4.2 Ma). The Hayakawa Volcanic Breccias overlies unconformably the middle Miocene (13 Ma) Yugashima Group. The Hayakawa Volcanic Breccias are andesitic to dacitic, and shallow marine sediments. Ages of sedimentary rocks were determined by microfossils and shell fossils, and sedimentary circumstance by shell fossils.

Sukumo river

Outcrop of the basaltic andesite dike intruded in tuff of the Hayakawa Volcanic Breccias. White crystals are anorthite. The pale brown color of some crystals is explained by fine brass (Zn-bearing copper) inclusion.

Reported Minerals

  • Anorthite
  • Brass(Zn bearing copper)
  • Cristobalite

Mineral Assemblages

  • Basaltic andesite (Host) - Anorthite
  • Basaltic andesite (Pore) - Cristobalite


Related Occurrences

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