Gonyerite

minerals

caryopilite

alleghanyite

berzeliite

Formula: Mn2+5Fe3+(Si3Fe3+O10)(OH)8
Phyllosilicate (sheet silicate), chlorite group
Specific gravity: 3.01
Hardness: 2½
Streak: Chocolate brown
Colour: Deep brown with reddish internal reflections
Solubility: Rapidly decomposed by cold concentrated hydrochloric acid and slowly by cold 3N hydrochloric acid with the separation of flaky-gelatinous silica; insoluble in cold concentrated sulphuric acid (Mindat)
Environments

Hydrothermal environments

Gonyerite occurs in veinlets in manganese-rich skarn associated with alleghanyite, baryte, bementite, berzeliite, garnet and jacobsite (Dana).

Localities

At the type locality, Långban, Filipstad, Värmland County, Sweden, gonyerite is found as radial aggregates of laths in hydrothermal veinlets cutting manganese skarn. Associated minerals include caryopilite, baryte, berzeliite, bementite and garnet (AM 40.1090-1094, Mindat, HOM).

At the Wesselsmine gonyerite has been found as thin bands in silica-rich areas, and as small crystals on hematite (Dana, R&M 85.4.323).

Common impurities: Al,Zn,Pb,Ca,F,Cl

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