Ferro-gedrite

minerals

enstatite

chamosite

cordierite

Formula: ☐Fe2+2(Fe2+3Al2) (Si6Al2)O22(OH)2
Inosilicate (chain silicate), amphibole
Specific gravity:
Hardness: 5½ to 6
Streak: White
Colour: Pale greenish-grey to brown
Common impurities: Ti,Mn,Ca,Na,K,F
Environments:

Metamorphic environments

Ferro-gedrite exists in low temperature, high pressure contact metamorphic geologic settings and remains stable up to 600°C-800°C due to its iron content (Wiki). Associated minerals include chamosite, chlorite, andalusite, cordierite, garnet, muscovite, biotite, spinel, quartz, anorthite variety labradorite, magnetite and graphite (HOM).

Alteration

gedrite-ferro-gedrite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
2(Mg,Fe2+)5Al4Si6O22(OH)2 + 4Si2 → 3(Mg,Fe2+)2Si2O6 + 2(Mg,Fe2+)2Al4Si5O18 + 2H2O
In the pyroxene-hornfels facies enstatite-ferrosilite may develop from gedrite-ferro-gedrite according to the above reaction (DHZ 2A p134).

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