Tags: Chemical Substance, Mineral.
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.
