Nsutite

nsutite

pyrolusite

cryptomelane

romanechite

Images

Formula: Mn2+xMn4+1-xO2-2x(OH)2x
Oxide, ramsdellite group, manganese-bearing mineral
Crystal System: Hexagonal
Specific gravity: 4.24 to 4.67 measured, 4.86 calculated
Hardness: 6½ to 8
Streak: Grey-black
Colour: Grey-black
Environments

Metamorphic environments

Nsutite is found in most major manganese deposits, where it is thought to be supergene, formed under alkaline oxidising conditions deficient in barium and potassium. Associated minerals include pyrolusite, cryptomelane, romanechite, chalcophanite, other manganese oxides, rhodochrosite, quartz and goethite (HOM). Manganoan nsutite typically is derived from the oxidation of manganese carbonate minerals such as rhodochrosite and kutnohorite, and nsutite is formed by the heating or further oxidation of manganoan nsutite (Dana).

Localities

At Ilfeld, Harztor, Nordhausen District, Thuringia, Germany, nsutite has been found, mixed with hollandite and other manganese oxide species, in a single specimen; tiny nsutite pseudomorphs after manganite crystals are discernable (Minrec 41.6.501).

The type locality is the Nsuta Mine, Tarkwa, Western Region, Ghana. Nsutite has been found as a major constituent in manganese ores from Nsuta and it has been reported from many other localitites worldwide. There is little doubt that nsutite will eventually be detected in manganese deposits throughout the world, and that it is much more abundant than ramsdellite. Characteristic of many occurrences of nsutite is its proximity to manganese carbonate. In some occurrences manganoan nsutite forms replacement veinlets in manganese carbonate rock. It then appears to be among the first oxides forming from the oxidation of manganese carbonate along with birnessite. In other specimens nsutite replaces other manganese minerals along fractures, along colloform banding, or diffusely. It appears to form at ambient temperatures in a slightly alkaline environment such as that caused by carbonate minerals in contact with oxygen-rich waters. It has never been found in typical hydrothermal assemblages (AM 47.246-266).

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