The Zombies Ate My Brains

Rescuing what might remain of the grey matter.

Mica

2012 Do these overalls make me look fat?

Mini-me and Mica

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”.

New Hampshire, circa 1908.
“Loading at a New England granite quarry.”

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

Samples such as those you'd find in a Kitchen, or heaven forbid, a monument showroom

Samples such as those you’d find in a Kitchen, or heaven forbid, a monument showroom

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/

Mr. Purdy and a sheet of mica from one of the largest crystals in the world

6 sides of the crystal

 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.

Muscovite from Boiling Springs, North Carolina - the green colour is caused by chromium

Muscovite from Boiling Springs, North Carolina.
The green colour is caused by chromium

 

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.

Muscovite and Feldspar from the Carey Quarry, Ontario

Muscovite and Feldspar from Ontario

mica fuse

mica fuse

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Categories: Mineral Collecting

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6 replies

  1. My all-time favorite mineral. As kids, we used to sit atop a huge boulder outside my father’s workplace in White Plains, NY, and peel off child-palm-sized pieces of mica. Wonderful. Many years later, I was intrigued to bump up against the word “isinglass” and read of its use for windows in Amish buggy curtains and later motored vehicles. I wondered then how, thin and bendy as it could be, mica could be flexible enough to be used in roll-up or fold-up vehicle curtains without breaking–for I remembered it as quite flaky and fragile. It was only as an adult that I mailed away for a set of 6 small samples of isinglass to see what it was like–and my questions remained. For the samples I received, about 3 x 4″ in size, were quite stiff, and surely would not have served well in those applications. Then, I learned of the two types of isinglass: One made from mica sheets, and the other from fish bladders. By then, my samples were long gone, and I still don’t know which they were, although, to me, they looked like the former(Maggie: What about the small sheet inside of your microwave?)

    Anyhow, my mica fascination has stayed with me. Driving cross-country in 2012, at Colorado’s Royal Gorge, while others were still staring at the gorge in the fading light of sunset, I was looking down at my feet on the clifftop, picking up the many pieces of mica glinting around them in the last orange glow.

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  2. Hi Babe! Thanks for your great post! Mica is quite brittle in my experience. IF indeed it was used as a roll-up blind, I wonder if it was pretreated in some fashion? Or perhaps fashioned in slats, like a bamboo blind?

    There is mica in my microwave?

    As I say, I’m a total newb at this minerals biz! Always more questions, and that’s a good thing!

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