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rock
rock  

Rock
Rock  
hello,

my fiance' and my self like to collect rocks and metal in the state of michigan; jackson specifically. we found a mysterious rock that is pure black in color and smooth but but very hard (pictures provided). this rock how ever looks very heavy; but it is in fact VERY light. My fiance's granny thinks it's petrified coal. but i'm not sure what it is. so if possible; could you tell me what sort of rock this is? pleas and thank you.

-Feenie

Answer
Hi Feenie,
Very cool rock.  The image I see is very blurry so I can't tell much from them, but your description is pretty clear.  You almost certainly have a piece of anthracite.  That's a variety of coal (so "granny" is partially correct).  This is a very pure coal with high caloric and carbon content.  It's harder than bituminous, is smooth and lustrous.  

There was a lot of coal mining going on about 100 years ago or less in the Jackson area (in fact there was an active coal mine within the walls of the State Prison of Southern Michigan in Jackson).  So it is not unusual to find some around.  The coal mines in Michigan were mostly bituminous and the coal didn't travel well or wasn't very good for heating, but there were anthracite localities.

Here's a site that has some info about coal, mostly anthracite:  

https://en.wikipedia.org/wiki/Anthracite

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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