Formula: Mn2+5Fe3+(Si3Fe3+O10)(OH)8
Phyllosilicate (sheet silicate), chlorite group,
manganese-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 3.01 measured, 3.03 calculated
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)
Common impurities: Al,Zn,Pb,Ca,F,Cl
Environments
Metamorphic 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).
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