Formula: ☐Fe2+2(Fe2+3Al2)
(Si6Al2)O22(OH)2
Inosilicate (chain silicate),
magnesium-iron-manganese amphibole subgroup,
amphibole supergroup, forms a series with
gedrite
Crystal System: Orthorhombic
Hardness: 5½ to 6
Streak: White
Colour: Pale greenish-grey to brown
Common impurities: Ti,Mn,Ca,Na,K,F
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,
iron-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).
Back to Minerals