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Tonosawa, 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.


Outcrop of a basaltic andesite dike intruded in tuff of the Hayakawa Volcanic Breccias. This photograph is a part of the dike. This dike is easily recognized as it is stronger for weathering than the host tuff. Clear anorthite phenocrysts less than 10 mm in length were observed. Width of photograph is approximately 30 cm.

Reported Minerals

  • Anorthite

Mineral Assemblages

  • Basaltic andesite (Host) - Anorthite


Related Occurrences

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