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Pink and black rocks1
Pink and black rocks1  

Pink and black rocks2
Pink and black rocks2  
Hi. Thanks for your time. Could you help me identify these pink and black rocks? They have a white streak, and they're fairly magnetic. I found them in my yard in south Mississippi.

Answer
Hi Tammy,
It looks like you have some samples of a metamorphic rock called a "gneiss". That's a rock that has undergone a lot of temperature and pressure; enough to change it physically and mineralogically.

Here's a site that shows a lot of different gneiss, both hand specimens and in the outcrop;

http://www.alamy.com/stock-photo/metamorphic-rock-gneiss.html

Here's another one;

http://www.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Gneiss.html

You mention you found them "fairly" magnetic.  A high concentration of iron can be magnetic.  Also, the mineral "magnetite" exhibits magnetism, and it can be present in metamorphic rocks.  I have not heard of magnetite being found in Mississippi but that doesn't mean it can't be.

I believe you have iron rich gneiss, but your best bet would be to take them to the geology department of a local university.  It's much easier to ID a rock when you can hold it, and it's been my experience that Geology Departments are happy to help the public.

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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