Get to Know a Mineral: Cummingtonite

As I am studying geology, I felt it would be nice to introduce some of the rocks and minerals that I look at in my studies. So let me introduce you to the world of geology!

To begin, a mineral must meet 5 criteria in order for it to be as such.
1. Occurs naturally
2. Solid
3. Formed by inorganic processes
4. A characteristic chemical composition
5. A crystal structure

A rock, on the other hand, is simply an aggregate of minerals. Rocks can be made up of many minerals or in some cases, just one.

The first mineral I would like you to get acquainted with is Cummingtonite. Go ahead, laugh..................................................now that you`re finished laughing, lets get to it.

Cummingtonite is a metamorphic amphibole with the chemical formula (Mg,Fe)₇Si₈O₂₂(OH)_2.
It was first described in 1824 near the town of Cummington, Massachusetts (hence the name). It is also found in Scotland, South Africa and Sweden.

Cummingtonite is commonly seen in metamorphosed magnesium rich rocks, but is also known to occur in some felsic igneous rocks like dacites. It can also be found in the iron formations of the Lake Superior region.

For all the geologists out there, here is a list of Cummingtonite`s properties:
Crystal System: Monoclinic
Crystal Habit: Fibrous, lamellar and radiated
Cleavage: Perfect {110}
Streak: White
Optic Sign: Biaxial (+)
Extinction: Inclined
2V: 65°- 98°

Also Get to Know:

Cummingtonite
Garnet