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Yoka

Futomi, Kamogawa city, Chiba pref., Japan

Occurrence

High-temperature zeolite facies metamorphic rocks

Zeolites produced in pockets of tholeiitic to alkali basaltic pillow lava and hyaloclastite of the early Miocene (20 Ma) Mineoka Group, an accretionary complex corresponding to the Setogawa Group of the Shimanto accretionary complex. Tholeiitic to alkali basalt is middle Eocene (47-38 Ma). Ages of sediments were determined by radiolarians, basalt by microfossils.

Reported Minerals

  • Calcite
  • Laumontite
  • Natrolite
  • Analcime
  • Thomsonite
  • Apophyllite-(KOH)
  • Enstatite
  • Magnesiohornblende

Mineral Assemblages

  • Natrolite - Thomsonite
  • Analcime
  • Gabbro(Host) - Magnesiohornblende
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