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i was breaking some rocks one day and a medium tan rock broke apart similar to shale and had a metallic formation inside. when i drew it out it it had a thin black layer on it but underneath looks similar to the crystal structure of steel with tightly packed small metallic crystals. it is rather heavy for its size and is not magnetic nor does it rust as a ferrous metal would. but for the life of me i cannot figure out what it is.the rock is the size of a black walnut with shell and weighs around 2 1/2 pounds.

Answer
Hi John,
Your specimen sounds very interesting.  You mention a "thin black" surface layer, that it's heavier than you think it should be, and that it has crystal structure that looks like steel.  All this shouts "meteorite" to me.  The thin black layer could be a fusion crust that forms when the meteor enters the atmosphere and the heat melts some of the crust.  Most meteors feel heavier than they appear because they often have a high concentration of Fe-Ni.  And when you section one and treat it with a certain acid you can see Widmanstatten patterns emerge that are the metallic crystals (http://www.arizonaskiesmeteorites.com/Widmanstatten/).

But you also mention it is non-magnetic.  

That could eliminate a meteorite from the discussion, except there is a type called a eucrite achondrite.  They belong to the "Stony" class of meteorite but these appear to be formed deeper in the crust of the parent body.  They look much like a terrestrial rock called granite where the mineral crystals that make up the rock are relatively large and conspicuous.  Perhaps they might appear metallic to you.  Another thing; the Widmansatten features aren't readily seen until the specimen is treated with nitric acid or ferric chloride.  So if structures are visible without etching the specimen it would appear what you see are not Widmansatten.

Here's a site that has some types of eucrite achondrites:

http://meteorites.pdx.edu/meteoriteid.htm

However, without a picture it's impossible to be sure.  You might want to take you rock to the geology or astronomy department of a local university.  They should be able to ID the rock for you.

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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