Birnessite

Field of view: 10 mm. A group of birnessite. The reniform black group is birnessite. The white part at the upper right is gangue quartz. The brown parts are dirt on the surface.

Recovered from a quartz vein of a moderate-temperature hydrothermal deposit associated with andesitic-basaltic pyroclastic rocks of an oceanic arc subjected to propylitization alteration.

Birnessite from this location was described in 1981.