After I posted my avatar several people wondered about the “thing” I was holding. It’s a large partial crystal of mica, probably the phlogopite variety.
As of last count, there are about 50 varieties of mica. It comes in assorted colours, white, pink, rose, lavender, yellow, gold, brown and black.
Those of you who have traveled along the highways in northern Ontario, through the Canadian Shield have seen the enormous outcrops of granite. In the US, New Hampshire is known as the “Granite State”.
Mica is one of those very common minerals. Add some quartz and feldspar and maybe a dash of hornblende, mix a little or a lot and you’ve got coarse or fine-grained granite. If you’ve got a granite counter-top or flooring, you’ve likely got mica in there somewhere. The mica component of rock is what makes them glint and glitter. It’s that exact property that is exploited by the cosmetics industry to create a sheen or sparkle.
Photo Credit : www.shorpy.com
In nature, mica can be found in crystal form, but in our area here in Ontario, it most often too ground up by geological moving and shaking. The last ice age pulverized anything on the surface and wiped it away. However, a few crystals did escape the purge. Some fairly large, as you can see by the photo of Mr. Purdy holding a sheet of mica.
Photo Credit http://geoscan.nrcan.gc.ca/
Mica crystals are six-sided. If you squint your eyes and use your imagination, you can make out the hexagonal shape of the crystal fragment I’m holding.
The crystals form in thin, flexible layers that are stacked to form what is called a “book”. The green specimen below is an example of muscovite that is coloured green due to the presence of chromium. It’s from Boiling Springs, North Carolina.
Relative to other minerals, the micas are light and soft. The layers and sheets of mica are flexible, heat-resistant and do not conduct electricity. These are the properties that are exploited in industry. The larger sheets like those that Mr. Purdy is holding are used as window panes in furnaces and stoves. We have an ancient corroded fuse similar to the one shown below. The window of the fuse is made of mica. Ground up mica is used in drywall joint compound and paints and in other applications it is used as a filler.
Categories: Mineral Collecting