Formula: Mn2+21Si8O27(OH)20
Inosilicate (chain silicate)
Specific gravity: 3.58
Hardness: 3
Streak: White
Colour: Colourless to pink
Solubility: Decomposed by hydrochloric acid

Metamorphic environments
Hydrothermal environments

Gageite is a rare manganese silicate.

Near Kuruman, South Africa, gageite is associated with leucophoenicite, hausmannite, rhodochrosite and manganoan calcite (HOM).

At the type locality, the Franklin Mine, Sussex county, New Jersey, USA, gageite is a late-stage, low to medium temperature mineral, implanted on other species in fissures and solution cavities, in a metamorphosed zinc-iron-manganese deposit (HOM, Webmin, Mindat, AM 53.309), associated with zincite, willemite, sclarite, pyrochroite, leucophoenicite, calcite and chlorophoenicite (HOM, Mindat).

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