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.

To silicate index.

Mineral group index.

Main index.

If you have some questions, suggestions or comments you are welcome to write me a line or two.