Phyllite

Rocks/Metamorphic

DSC_0896

Here in central Massachusetts, a rock I commonly come into contact with is phyllite. Normally, when I find phyllite, it generally tends to be one of the least interesting rocks around, so I figure what better way to make it more interesting than to research it, and write about it, right? So here it goes:

Common throughout much of New England,[i] it is also especially common out my way because it is one of the rocks that make up the Worcester Formation which is found just to the north of me.[ii] Although it is not part of the bedrock where I live, it is commonly found here because it was deposited here by the last glacial advance several thousand years ago.[iii]

 

Properties of Phyllite

Phyllite is classed as a regional metamorphic rock,[iv] which means it was formed by immense heat and pressure deep in the earth’s crust as a result of mountain building.[v] The heat and pressure recrystallized the original rock which was often originally slate, which in turn was often shale or mudstone.[vi] The most common minerals found in phyllite are quartz, chlorite and most importantly: muscovite mica.[vii] The mica is what gives it its silky luster.[viii] Also, the heat and pressure that formed the rock also warped it to give the rock a wavy appearance.[ix] Another important characteristic of the rock is that the mica and chlorite crystals in the rock are almost always microscopic.[x] I have often encountered large quartz lenses in the phyllite that I find in central Massachusetts.

Another interesting thing about phyllite is that is has very little economic use.[xi] Basically, if you find it there isn’t a whole hell of a lot you can do with it. So it adds little to the local economy, but on the other hand, I don’t have to worry about pollution from mining either. So I guess that is a good thing.

The phyllite in the picture above was taken from Wachusett Reservoir in West Boylston, MA.  In fact, that particular place is a very nice, quiet spot to just relax and reflect, and not too far from the popular abandoned Old Stone Church in which many locals often visit.

Well, guess I made it a little more interesting anyway. I hope you agree.

[i] Edited by Prinz, Martin, George and Peters, Joseph of the American Museum of Natural History “Simon and Schuster’s Guide to Rock s & Minerals” Entry 353. Fireside Books Published by Simon and Schuster, 1978. New York

[ii] Skehan, James “Roadside Geology of Massachusetts” Pg. 181. Mountain Press, 2001. Missoula, Montana.

[iii] Skehan, James “Roadside Geology of Massachusetts” Pg. 21. Mountain Press, 2001. Missoula, Montana.

[iv] [iv] Edited by Prinz, Martin, George and Peters, Joseph of the American Museum of Natural History “Simon and Schuster’s Guide to Rock s & Minerals” Entry 353. Fireside Books Published by Simon and Schuster, 1978. New York

[v] Chesterman, Charles W. along with Lowe, Kurt (scientific consultant) “National Audubon Society Field Guide to Rocks and Minerals” pg. 732. Chanticleer Press 1979. New York

[vi] Chesterman, Charles W. along with Lowe, Kurt (scientific consultant) “National Audubon Society Field Guide to Rocks and Minerals” pg. 732-3. Chanticleer Press 1979. New York

[vii] Chesterman, Charles W. along with Lowe, Kurt (scientific consultant) “National Audubon Society Field Guide to Rocks and Minerals” pg. 732. Chanticleer Press 1979. New York

[viii] Chesterman, Charles W. along with Lowe, Kurt (scientific consultant) “National Audubon Society Field Guide to Rocks and Minerals” pg. 732. Chanticleer Press 1979. New York

[ix] Chesterman, Charles W. along with Lowe, Kurt (scientific consultant) “National Audubon Society Field Guide to Rocks and Minerals” pg. 732. Chanticleer Press 1979. New York

[x] Edited by Prinz, Martin, George and Peters, Joseph of the American Museum of Natural History “Simon and Schuster’s Guide to Rock s & Minerals” Entry 353. Fireside Books Published by Simon and Schuster, 1978. New York

[xi] Chesterman, Charles W. along with Lowe, Kurt (scientific consultant) “National Audubon Society Field Guide to Rocks and Minerals” pg. 732. Chanticleer Press 1979. New York

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