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Geology/All white obsidian with blue in it?


QUESTION: I live in northwest Ohio while fishing the river in my back yard. I found two chunks of what looks like white obsidian with blue streaks in it. But online I cant find anything like it i have large chunks of black obsidian found in the fields but never white it looks the same there about baseball sized i have photos i can e-mail there glass looking I'm lost on what it is and if its worth anything

ANSWER: Hi William,
Go ahead and send another question with the images.  I think you may have is chert; the light colored equivalent of flint.  It looks much like obsidian and fractures the same way.  Do a quick search on the Net for chert and you'll find some good examples.

Hope this helps.

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I dont know?
I dont know?  

What is it
What is it  
QUESTION: Here is two photos can you tell me if it is chert i looked it up its close

Thanks for writing me back Bob

Hi again William,

I'm pretty sure you have a piece of glass slag.  That's a waste product from the smelting of iron ores.  All the silicates that are present in the raw ore are removed during the beneficiation process and usually collect on the refractory walls or can be removed mechanically from the furnace.  They can be pretty much any color and are glassy in appearance, although some slag can be metallic.  

Your's is a fine looking piece.  Some people find them very collectable and they were used for, among other things, jewelry in the 19th century.  

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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