Mineral description : Cummingtonite

Cummingtonite from Västra Silvberg.
Variety : silvbergite.

Mineral class Silicates : Inosilicates : Cummingtonite - Anthophyllite group.
Chemical formula (Mg,Fe)7(OH/Si4O11)2
Crystal system  
Habitus As radiating or stalky aggregates.
Cleavage Good along [110)
Hardness 5-6
Density 3.1-3.7 (higher with increasing iron content)
Color Light brown.
Streak  
Luster Vitreous to silky.
Description  
Occurance  
Associates  
Notes Separated from anthophyllite by clearly visible polysynthetic twinning in cummingtonite (along [100]).
Creates a continuous serie with Grunerite.
Manganous cummite is called silvbergite.
( NOTE : I have twoo books where one tells me that silvbergite is an anthophyllite (Mineral i Sverige) and the other that it is a cummingtonite (Mineral och Bergarter), what shall i trust.)
Locations A common mineral in Sweden.
  • Persgruvan, Riddarhyttan, Västmanland.
  • Mossgruvan, Ludvika.
  • Persberg mining district.
  • Nordmark mining district.
  • Västra Silvberg mining district. As golden brown aggregates of silvbergite.

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axelsson@acc.umu.se
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Last changed : 1998-07-30