General Information:
Chemical Formula:
Mn++3[Mn++3Fe+++][(Si,Fe+++)4O10](OH,O)8
Composition:
(Molecular Weight = 703.49 gm)
Magnesium 10.36 % Mg
Manganese 23.43 % Mn
Iron 9.53 % Fe
Silicon 15.17 % Si
Hydrogen 0.57 % H
Oxygen 40.94 % O
Empirical Formula:
Mg3Mn2+3Fe3+Si3.8Fe3+0.2O14(OH)4
Environment:
Veinlets im Mn-rich skarns.
Locality:
Langban, Varmland, Sweden.
Name Origin:
Named for Forest A. Gonyer (1899-1971), chemist-analyst and mineralogist, Harvard University.
Physical Properties:
Cleavage:
[001] Perfect
Color:
dark brown, brownish black, or bright green.
Density:
3.01
Diaphaniety:
Transparent to Translucent
Habits:
Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite), Platy - Sheet forms (e.g. micas).,
Hardness:
2.5 - Finger Nail
Luster:
Pearly
Streak:
chocolate brown
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