Gedrite

inosilicate

metamorphic

Formula: ☐Mg2(Mg3Al2)(Si6Al2)O22 (OH)2
Inosilicate (chain silicate), amphibole
Specific gravity:
Hardness: 5½: to 6
Streak: White
Colour: Pale greenish-grey to brown
Environments:

Metamorphic environments

Gedrite occurs in contact and medium to high grade metamorphic rocks where it may be associated with garnet, cordierite, anthophyllite, cummingtonite, sapphirine, sillimanite, kyanite, quartz, staurolite or biotite.

Alteration

gedrite-ferro-gedrite and quartz to enstatite-ferrosilite, Fe-rich cordierite and H2O
(Mg,Fe2+)5Al4Si6O22(OH)2 + 2Si2 → 3(Mg,Fe2+)SiO3 + (Mg,Fe2+)2Al4Si5O18 + H2O
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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