Rhodochrosite

minerals

groutite

rhodonite

sturmanite

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Formula: Mn(CO3)
Carbonate, manganese mineral
Specific gravity: 3.3 to 3.6
Hardness: 3½ to 4
Streak: White
Colour: Rose-pink, light red, yellowish grey, brownish
Solubility: Slightly soluble in water with the solubility rate increasing with the presence of CO2. Begins to dissociate at about 300˚ with the formation of CO2 and MnO. Moderately soluble in hydrochloric, sulphuric and nitric acid.
Common impurities: Fe,Ca,Mg,Zn,Co,Cd
Environments:

Pegmatites
Metamorphic environments
Hydrothermal environments

Rhodochrosite is a comparatively rare mineral, occurring as a primary mineral in epithermal (low temperature), mesothermal (moderate temperature) and hypothermal (high temperature) hydrothermal veins, with ores of silver, lead, copper, and other manganese minerals. It also occurs as large deposits in metamorphic rocks, and the alkaline syenite pegmatites of Mont Saint-Hilaire, Canada (R&M 93.2.147)

Localities

At Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, rhodochrosite pseudomorphs after fluorite and after serandite have been found (KL p162, 163).

At the Oppu mine, Japan, rhodochrosite pseudomorphs after calcite have been found (KL p161).

At the NChwaning mine, Kalahari manganese fields, South Africa, rhodochrosite pseudomorphs after sturmanite and andradite pseudomorphs after rhodochrosite have been found (KL p164).

At the Magma mine, Pioneer District, Pinal county, Arizona, USA, rhodochrosite has been found in the matrix of groutite specimens, and as massive material associated with chalcopyrite (R&M 95.1.87).

At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, rhodochrosite occurs as crystals to 3 cm in miarolitic cavities, and as masses in phosphate pods. In a large mass of rhodochrosite-siderite after lithiophilite, millimeter-sized sphalerite crystals associated with perloffite have been noted. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.514).
Near the contact with lithiophilite the rhodochrosite crystals are partially replaced by hureaulite and reddingite. Near the top of the lithiophilite in some areas rhodochrosite replaces lithiophilite. Associated with this replacement rhodochrosite are several manganese-rich phosphates, including strunzite, jahnsite-group species, pseudolaueite, laueite and stewartite (R&M 95.2.166).

Alteration

braunite and CO2 to rhodochrosite, rhodonite and O2
2Mn2+Mn3+6O8(SiO4) + 12CO2 ⇌ 12MnCO3 + 2Mn2+SiO3 + 3O2
Increasing temperature favours the forward reaction (AM80.571).

rhodochrosite to manganosite and CO2
MnCO3 ⇌ MnO + CO2
Increasing temperature favours the forward reaction (AM80.571).

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

rhodochrosite and O2 to hausmannite and CO2
6MnCO3 + O2 ⇌ 2Mn2+Mn3+2O4 +6CO2
(AM80.571)

rhodochrosite and O2 to pyrolusite and CO2
2MnCO3 + O2 ⇌ 2Mn4+O2 + 2CO2
(AM80.571)

rhodochrosite and quartz to rhodonite and CO2
MnCO3 + SiO2 ⇌ Mn2+SiO3 + CO2
This is a metamorphic reaction occurring in manganese deposits and manganese-rich iron formations. Increasing temperature favours the forward reaction (MOM p487, AM80.571).

rhodochrosite, SiO2 and O2 to braunite and CO2
14MnCO3 + 2SiO2 + 3O2 ⇌ 2Mn2+Mn3+6O8(SiO4) ⇌ 14CO2
Increasing temperature favours the forward reaction (AM80.571).

rhodonite and rhodochrosite to tephroite and CO2
Mn2+SiO3 + Mn(CO3) ⇌ Mn2+2(SiO4) + CO2
Increasing temperature favours the forward reaction (DHZ 1A p344, 348, AM80.571).

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