Bixbyite-(Mn)

bixbyite-(Mn)

topaz

rhodochrosite

hausmannite

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Formula: Mn³⁺₂O₃
Simple oxide, manganese-bearing mineral, forms a series with bixbyite-(Fe)
Crystal System: Isometric
Specific gravity: 4.945 measured, 5.031 calculated
Hardness: 6 to 6½
Streak: Black
Colour: Black
Common impurities: Al,Mg,Si,Ti
Environments:

Volcanic igneous environments
Metamorphic environments
Hydrothermal environments

Localities

At Långban, Sweden, bixbyite-(Mn) occurs in metamorphosed manganese ores (Dana).

At the Black Range tin district, New Mexico, USA, bixbyite-(Mn) occurs in rhyolite (Dana).

At the type locality, Maynard's mine, Pismire Knolls, Thomas Range, Juab County, Utah, USA, bixbyite-(Mn) occurs in lithophysal cavities in rhyolite. Associated minerals include topaz, sanidine, quartz, pseudobrookite, hematite and beryl (Mindat).

At Topaz Mountain, Thomas Range, Juab County, Utah, USA, bixbyite-(Mn) occurs in cavities in rhyolite associated with topaz, spessartine, red beryl and hematite, also with fluorite (Dana).

Alteration

bixbyite-(Mn) and O₂ to pyrolusite
2Mn₂O₃ + O₂ ⇌ 4MnO₂
Increasing temperature favours the forward reaction (AM80.571).

bixbyite-(Mn) and quartz to braunite and O₂
14Mn₂O₃ + 4SiO₂ ⇌ 4Mn²⁺Mn³⁺₆O₈(SiO₄) + O₂
(AM80.571)

hausmannite and O₂ to bixbyite-(Mn)
4Mn²⁺Mn³⁺₂O₄ + O₂ ⇌ 6Mn₂O₃ (AM80.560-575)

rhodochrosite and O₂ to bixbyite-(Mn) and CO₂
4MnCO₃ + O₂ ⇌ 2Mn³⁺₂O₃ +4CO₂
Increasing temperature favours the forward reaction (AM80.571).

The diagram below is a Pourbaix diagram for manganese (GSJ). It shows the relationship between akhtenskite MnO₂, bixbyite-(Mn) Mn₂O₃ and hausmannite Mn₃O₄.


























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