Birnessite

Birnessite (Na_0.3Ca_0.1K_0.1Mn⁴⁺Mn³⁺O₄·1.5(H₂O)) is an mineral oxide 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 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.

It was first described in 1956 and named for an occurrence in Birness, Aberdeenshire, Scotland.

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v • d • e Manganese minerals

Borates	Sussexite · Tusionite

Carbonates	Ankerite · Kutnohorite · Rhodochrosite · Manganoan Calcite

Oxides	Birnessite · Bixbyite · Ferrocolumbite · Ferrotantalite · Galaxite · Glaucochroite · Hausmannite · Hübnerite · Jacobsite · Manganite · Manganotantalite · Nsutite · Psilomelane · Pyrolusite · Romanèchite · Tantalite · Todorokite · Umber · Wolframite

Phosphates	Childrenite · Graftonite · Lithiophilite · Natrophilite · Purpurite · Triplite · Triploidite · Zanazziite

Silicates	Babingtonite · Bixbite · Braunite · Calderite · Chloritoid · Eudialyte · Jeffersonite · Knebelite · Ottrelite · Piemontite · Pyroxferroite · Rhodonite · Spessartine · Sugilite · Tephroite · Zakharovite · Zircophyllite

Sulfides	Alabandite · Hauerite · Rambergite

Other	Axinite (borosilicate) · Geigerite (arsenate) · Manganese nodule (various) · Zincobotryogen (sulfate)