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Geology/what kind of rock is this?


my rock
my rock  
I found it awhile back and thought it was cool. Can you tell me what it is?

Hi Kimmi,
This is a good picture.  It looks like a mineral cluster to me.  The mineral appears tabular (you can see the edges of each crystal).  It's mostly dark colored but the lower section looks glassy.  

Unfortunately there are a lot of tabular, glassy minerals.  I'm not sure I can be definitive but I think I can get pretty close.  

Is it soft?  Can you scratch it with your fingernail?  If so, it probably is gypsum.  Here's a picture of a more clean gypsum cluster.  I couldn't find one that looks exactly like your specimen but this gives you an idea of the structure.

If you can't scratch it with a fingernail, does it feel heavier than you think it should for its size?  If so, it might be barite.  Here's a couple pics that will give you an idea.

There is another mineral called celestite that could look like this but I doubt that's what it is.  Without actually holding your specimen it's pretty hard to identify it but I think you have gypsum.  If you want a more definite answer you should contact the geology department of your local university.  If you know of a Rock Club someone in there should know what you have.  I have found that local collectors are a very reliable source of information.

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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