Rhodonite

pyroxmangite

braunite

Formula: Mn2+SiO3
Inosilicate (chain silicate), manganese mineral. Rhodonite and pyroxmangite are polymorphs; pyroxmangite is the high temperature, low pressure polymorph (Mindat).
Specific gravity: 3.57 to 3.76
Hardness: 5½ to 6½
Streak: White
Colour: Red, pink, brownish-red, gray
Solubility: Slightly soluble in hydrochloric acid
Environments:

Sedimentary environments
Metamorphic environments
Hydrothermal environments

Rhodonite is found in manganese bearing deposits formed by hydrothermal, contact and regional metamorphic and sedimentary processes.

Alteration

braunite to hausmannite, rhodonite and O2
2Mn2+Mn3+6O8(SiO4) ⇌ 4Mn2+Mn3+2O4 + 2Mn2+SiO3 + O2
A higher temperature favours the forward reaction (AM80.565).

braunite and CO2 to rhodochrosite, rhodonite and O2
2Mn2+Mn3+6O8(SiO4) + 12CO2 ⇌ 12MnCO3 + 2Mn2+SiO3 + 3O2
A higher temperature favours the forward reaction (AM80.565).

braunite and quartz to rhodonite and O2
2Mn2+Mn3+6O8(SiO4) + 12SiO2 ⇌ 14Mn2+SiO3 + 3O2
A higher temperature favours the forward reaction (AM80.565).

hausmannite and quartz to rhodonite and O2
2Mn3O4 + 6SiO2 ⇌ 6Mn2+SiO3 + O2
A higher temperature favours the forward reaction (AM80.571).

hausmannite and rhodonite to tephroite and O2
2Mn3O4 + 6Mn2+SiO3 ⇌ 6Mn2+2SiO4 + O2
A higher temperature favours the forward reaction (AM80.565).

johansennite and H2O to rhodonite and xonotlite
6CaMnSi2O6 + H2O → 6Mn2+SiO3 + Ca6Si6O17(OH)2
At Pueblo, Mexico, johansennite occurs in calcite veins in rhyolite and is altered to rhodonite and xonotlite according to the above equation (DHZ 2A p421).

manganosite and quartz to rhodonite
MnO + SiO2 ⇌ Mn2+SiO3
(AM80.561)

manganosite and rhodonite to tephroite
MnO + Mn2+SiO3 ⇌ Mn2+2SiO4
(AM80.560-575)

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. A higher temperature favours the forward reaction (MOM p487, AM80.568).

rhodonite and braunite to tephroite and O2
10Mn2+SiO3 + 2Mn2+Mn3+6O8(SiO4) ⇌ 12Mn2+2(SiO4) + 3O2
(AM80.571)

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

tephroite and quartz to rhodonite
Mn2+2(SiO4) + SiO2 → 2Mn2+SiO3
(AM80.571)

Common impurities: Al,Ca,Fe,Zn

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