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Kunikami, Minano city, Chichibu county, Saitama pref., Japan




Greenschist facies serpentinite

Serpentinite 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). This serpentinite block contais calcite veins, and mined as ophicalcite. This serpentinite block is lens-shaped and is concordant with schistosity of the Sambagawa metamorphic rocks. The Sambagawa metamorphic rocks are considered that it has been near the ground surface since early Paleocene (65 Ma). The origin of this serpentinite block is considered as sedimentary serpentinite mélange from serpentinite seamounts at the fore-arc slope. Metamorphic age was determined by K-Ar radiometric dating of muscovite.


Outcrop of serpentinite associated with calcite veins in Sambagawa Metamorphic Rocks. This serpentinite was mined for construction material by the name "Ophicalcite". White veins in this photograph are calcite, and tremolite veins may be included in other parts of this locality. The dark reddish-green host is serpentinite. Calcite veins are undulated and do not last long. Veins are aligned in a direction, not randam.

Reported Minerals

  • Tremolite
  • Calcite
  • Talc

Mineral Assemblages

  • Serpentinite - Tremolite
  • Serpentinite - Calcite
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