Montmorillonite
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.
Other localities
- Bentenzaki (Smectitization, Massive)
- Morocco (Smectitization, Massive)
- Hirasawa (Alpine Fissure, Pink)