TrekGEO > Mineral Trail > Koshinetsu region > Nagano pref. > Goethite

Japanese page


Mount Takeshi

Shimo-Takeshi, Ueda city, Nagano pref., Japan

Closed to collecting as it is a natural monument of Ueda city

IMA approved name

Goethite pseudomorph after pyrite


Width of the cubic crystal: 10 mm. Goethite replacing pyrite. The brown host is metasomatised rhyolite - dacite tuff of Reisenji Volcanics Member, Uchimura Formation.

Recovered from a meteoric oxidation zone of metasomatised tuff.

The first Goethite pseudomorph after pyrite from Japan was reported from this location in 1893.

The formation process of this specimen is considered by reactions relating iron bacteria in oxygen-containing meteoric water. For example:

[Inorganic reaction]

2FeS2 (Pyrite) + 7O2 + 2H2O = 2Fe2+ + 4SO42- + 4H+

[Iron bacteria]

4Fe2+ + O2 + 4H+ = 4Fe3+ + 2H2O

[Inorganic reaction]

4Fe3+ + 2H2O + 3O2 = 4FeOOH (Goethite)

Other localities

Copyright (c) 2024 NariNari, All Rights Reserved.