TrekGEO > Mineral Trail > Kanto region > Saitama pref. > Hosoyama

Japanese page

Hosoyama

Shiroishi, Higashi-Chichibu city, Chichibu county, Saitama pref., Japan

Occurrence

Serpentinization

Serpentinite of the Mikabu Greenrocks associated with the Middle Jurassic (170 Ma) Kamiyoshida unit or the Early Cretaceous (120 Ma) Kashiwagi unit, members of the Northern Chichibu accretionary complex. The Mikabu Greenrocks is probably a part of the Middle Jurassic to Early Cretaceous accretionary complex cropped out between the Nothern Chichibu acretional complex and the Sambagawa metamorphic rocks. The Mikabu Greenrocks are composed of Carboniferous to Triassic Basalt lava, basaltic tuff breccia, basaltic tuff, and gabbro, and has been subjected to Pumpellyite-Actinolite facies metamorphism as a low grade part of the Sambagawa metamorphic belt in the Late Cretaceous (100 Ma). The protolith of the Mikabu Greenrocks is considered as mafic volcanic rocks and ultramafic rocks of oceanic plateaux and seamounts. Serpentinite is possibly serpentinite seamount and/or sedimentary serpentinite at the fore-arc slope. Ages of sedimentary rocks were determined by conodont, and metamorphic age by K-Ar or Ar-Ar radiometric dating of muscovite. Ophicalcite was mined for construction material.

Hosoyama

Outcrop of serpentinite from Mikabu Greenstones. The green host is serpentinite. The front face of the outcrop is along the vein of fibrous white chrysotile. Chrysotile is fine white fibers which come loose easily by hands. Antigorite is rough green fibers which does not come loose.

Reported Minerals

  • Antigorite
  • Chrysotile
  • Talc
  • Calcite
  • Grossular
  • Aragonite

Mineral Assemblages

  • Serpentinite - Calcite
  • Talc - Grossular - Unspecified
  • Antigorite - Chrysotile
Copyright (c) 2020 NariNari, All Rights Reserved.