TrekGEO > Mineral Trail > Koshinetsu region > Yamanashi pref. > Montmorillonite

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Hirasawa Mine

Enzan-Hirasawa, Koshu city, Yamanashi pref., Japan

This locality is closed to collecting.

Source for bentonite


Field of view: 20 mm. Montmorillonite formed by alteration of orthoclase. The pink to white earthy part is montmorillonite. The surrounding white parts with a vitreous luster are quartz. The black grains are biotite, and the brown parts are limonite crusts.

Recovered from a titanium type rare-element pegmatite in the S-type (Ilmenite-series) margin of I-type (Magnetite-series) granite formed by the reduction reation of granite magma with pelitic rocks. Formed in the Middle Miocene (10 Ma).

Montmorillonite from this location was described in 1963.

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