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Geology/gray rock with holes

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Question
nephele1
nephele1  

nephele2
nephele2  
Here is a picture of the rock.  Sorry about not attaching it first.  Thank you.

Answer
Hi again Jenny,
That's a good pic.  I think you have piece of basalt.  That's a rock that hardens directly from molten rock.  Lava is molten rock that flows out on the surface, magma remains buried.  Lava hardens into rock quickly and so the grains that make it up are VERY small.  As I mentiomed in our first message the Sierra Nevadas are mostly granite but this shows that there certainly must be some basalt.  And that is pretty common.  
The holes that you see were filled with minerals.  Not sure what they might have been, but over the years they have popped out leaving the holes behind.  Another thing that they could be is gas pockets, vesicles.  What happens is that gas from the melted rock collects in pockets in the rock while it is still molten.  Later, after the rock hardens, the gas leaks away leaving holes.  This is what I think you have.
Here's a site that shows a rock that is much like yours, but I think yours is a bit more smoothed by erosion

http://geology.about.com/od/more_igrocks/ig/extrusives/basalt_hawaii2.htm

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.

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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.

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Michigan Basin Geological Society

Publications
Decade of North American Geology.
Bedrock Geology of Michigan

Education/Credentials
BS Wayne State University

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