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Question
Rock or mineral
Rock or mineral  

Large black rock
Large black rock  
We found these while hiking in Harriman State park in NY.

Do you know what kind of rocks or minerals these are?  The larger one is mostly black, some specs of reddish brown and a section of grey.  It also appears to shine when rotating in sun light.

The smaller one appears to be copper.

Many thanks, mike

Answer
Hi Mike,
Looks like you have a couple schist specimens.  That's a metamorphic rock; one that has been subjected to moderate amounts of temperature and pressure.  There was not enough temperature to melt the rock but enough to change the minerals in it.  This kind of rock is usually associated with mountain building episodes.  Here's a picture that looks much like yours.  The reddish specs are probably garnets.  The shiny spots are mica.

http://csmres.jmu.edu/geollab/fichter/MetaRx/Rocks/schist1.html

From your picture, the smaller rock does not look like copper.  It probably is the same type of rock.  It's difficult to tell but I think that's the case.

Hope this helps.
Bob

Geology

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C. Robert Reszka, Jr.

Expertise

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.

Experience

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.

Organizations
Michigan Basin Geological Society

Publications
Decade of North American Geology.
Bedrock Geology of Michigan

Education/Credentials
BS Wayne State University

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