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Geology/rock identification


Shiny Rock
Shiny Rock  

I found this rock in my backyard in Michigan. It looks like it has some clear quartz crystal in it. It appears like stacked flakes and is quite shiny and silver-colored. Do you know what kind of rock this might be? It's size is about 1 inch by 1 inch. Thank you in advance.

Hi Cornelia,
You have a piece of muscovite there.  That's a type of mica, a mineral with a very complex formula.  It is not particularly rare but you usually don't find it in your backyard, unless it's a gravel pit or quarry.  

The mineral forms soft, flat plates that kind of grow together in book-like structures.  In fact collectors speak of finding "mica books".  You can separate the sheets until they are only a few molecules thick.  They can be made so thin that you can see through them and they were used as a substitute for glass.  They used to be called "isinglass" and could be used in furnace doors so you could see the flames, since muscovite is heat resistant and a good insulator.  

It gets it name from Muscovy-glass because people in Russia used it as a replacement for glass in their windows.

Here's a couple pictures.  The second looks a bit more like your specimen while the first is a more representative example of a mica:   good pic of muscovite

Hope this helps


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C. Robert Reszka, Jr.


I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.


I have been working for the State of Michigan for 36 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.

Michigan Basin Geological Society

Decade of North American Geology.
Bedrock Geology of Michigan

BS Wayne State University

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