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Joshin Mine

Hoshimata, Tsumagoi city, Agatsuma county, Gunma pref., Japan


Neutral metasomatic rocks of Halloysite zone

Halloysite-10Å deposit formed by hydrothermal alteration of andesitic tuff of Middle Pleistocene (0.49 Ma) Nittazawa Lavas erupted from Urakurayama volcanic edifice, Azumaya volcano. It is considered that halloysite was formed by acidic alteration of anorthite in andesite. Ages of volcanic rocks were determined by K-Ar radiometric dating.

Joshin Mine

Furnace heritages used to produce fire clay by dehydrating halloysite ore.

Reported Minerals

Mineral Assemblages

  • Andesite(Host) - Halloysite-10Å

Details of the mine

Joshin mine was first developed to mine aluminum during world war II. After the war, halloysite was mined for material of firebrick.


  • 1940: Ore was found by Ishizo Hoshikawa during building a charcoal kiln.
  • 1941: World War II was started.
  • 1943: Aluminum mining was planned by the military authorities.
  • 1945: The end of the war.
  • 1957: The first furnace was built.
  • 1963: The mine was closed because of a fire.


Related Occurrences

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