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Tateya, Akiruno city, Tokyo, Japan


Water bottom deposits

Glendonite, mineral-like material, formed on the sea floor during deposition of mudstone-sandstone alternating beds of the early Miocene (19 Ma) Kosho Formation. The Kosho Formation is composed of abyssal sediments. The Kosho Formation conformably overlies the conglomerate-dominant Uchimura Formation, and conformably underlies the mudstone-dominant Aoki Formation. Ages of sedimentary rocks were determined by microfossils and fossil bivalvia.


Glendonite in mudstone of the Kosho Formation. A light gray twinned glendonite is at the right of the scale coin. Two long bipyramidal crystals of glendonite form a X-shaped twin-like structure. The flat surface of this outcrop is a bedding plane of mudstone along the boundary between mudstone and sandstone in alternating beds of them. Glendonite is parallel to sub-parallel to the bedding plane.

Reported Minerals

Mineral Assemblages

  • Glendonite


  • Tateya (Glendonite)
  • Kodo (Glendonite)
  • Iseyama (Glendonite)
  • Teradomari (Glendonite)
  • (Methane hydrate)

Related Occurrences

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