Greenalite

phyllosilicate

sedimentary

Formula: (Fe2+, Fe3+2-3Si2O5(OH)4 phyllosilicate (sheet silicate) serpentine group
Specific gravity: 2.85 to 3.15
Hardness: 2½
Streak: Greenish grey
Colour: Green, light yellow-green
Environments:

Sedimentary environments

Greenalite is a primary phase in some banded iron formations

Alteration

Mg-rich greenalite to olivine, Mg-rich grunerite and H2O
18(Fe2+, Mg))3Si2O5(OH)4 → 20(Fe,Mg)2SiO4 + 2(Fe2+,Mg)7Si8O22(OH)2 + 34H2O
(DHZ 1A p266)

Mg-rich greenalite to olivine, SiO2 and H2O
2(Fe2+, Mg))3Si2O5(OH)4 → 3(Fe,Mg)2SiO4 + SiO2 + 4H2O
(DHZ 1A p265)

Common impurities: Al,Mn,Mg

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