TrekGEO > Mineral Trail > Kanto region > Saitama pref. > Kami-Nagatoro

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Kami-Nagatoro, Nagatoro city, Chichibu county, Saitama pref., Japan

Closed to collecting as it is a natural monument.


Greenschist facies metamorphic rocks

Tuff in the Late Jurassic (150 Ma) to Early Cretaceous (130 Ma) accretionary complex subjected to Greenschist facies metamorphism as a part of the high-P Sambagawa metamorphic belt in the Late Cretaceous (70 Ma). The Sambagawa metamorphic rocks is considered that it has been near the ground surface since early Paleocene (65 Ma). Metamorphic age was determined by K-Ar radiometric dating of muscovite.


Outcrop of stilpnomelane schist of Sambagawa Metamorphic Rocks. This outcrop is called as "Tora-iwa" ("Tiger rock" in Japanese) by local people because it looks like the pattern of tiger fur. Dark brown parts are rich in stilpnomelane. The white veins perpendicular to the schistosity are fibrous calcite, and it grows perpendicular to the vein walls. There are tiny octahedral magnetite crystals on the surface of the outcrop.

Reported Minerals

  • Stilpnomelane
  • Calcite
  • Magnetite
  • Malachite
  • Copper

Mineral Assemblages

  • Stilpnomelane - Calcite - Magnetite
  • Malachite - Copper
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