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birnessite
Birnessite (Na0.3Ca0.1K0.1)(Mn4+,Mn3+)2O4 · 1.5 H2O is an oxide mineral of manganese along with calcium, potassium and sodium. It has a dark brown to black color with a submetallic luster. It is also very soft, with a Mohs hardness of 1.5. Birnessite is formed by precipitation in lakes, oceans and groundwater and is a major component of desert varnish and deep sea manganese nodules.
==History==
It was first described in 1956 and named for an occurrence in Birness, Aberdeenshire, Scotland. Birnessite is found as an oxidation product of several other minerals, including rhodonite, rhodochrosite, and as a weathering product of franklinite-wilminite ore. It has also been found as a coating along joint planes and fractures within a trachyte sill. However, it has been most commonly seen as a constituent of oceanic nodules of manganese.
A recent study found that the mineral is able to break down prions via oxidation. How well this process works outside the laboratory is unclear.〔http://www.sciencedaily.com/releases/2009/01/090114142028.htm Common Soil Mineral Degrades The Nearly Indestructible Prion〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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