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Geology/Obsidian found in Michigan? Unknown rocks found


Unknown Michigan Rocks Found
Unknown Michigan Rocks  

Pic Two; Unknown Michigan Rocks Found
Pic Two; Unknown Michi  
Hello Robert.  My name is Tammy and I too found a localized, small area of Obsidian rock in Northern Michigan this summer of 2014 with all the same colors as Scott described. They are glassy, fine grained (look semi-precious),dark black,light grey and emerald green in color. I found mine, which totals to the sum of about 200 rocks collected, along side a railroad track.  I surmised at this point that the Obsidian or what ever these rocks may be, must have came from a "rock quarry" as the Obsidian appeared (unknowingly)dumped right along with the other stones from the rock quarry company. This means that what ever rock quarry company that unknowingly dumped these semi-precious stones, must
have a very deep basin that they dig rocks from, thus, most likely then an older quarry company? Though, I agree with Scott, in that I also feel that these rocks will come up "unknown".  Why?  Well, strangely enough, not only did I find the rocks in a condensed area but the rocks were scattered in a trail formation, many were imbedded into the ground and not only this but along side this trail of rocks were "freshly" broken off tree branches, not to mention all the skid marks dug into the dirt along this trail.  I do have pictures of this whole scene, the trail of broken branches and skid marks. Taking all this evidence into consideration, I also came to the conclusion that what I may possess may be remnants of a meteor? How do I send you pictures and physical samples of these rocks? Thank you, Tammy

Hi Tammy,
As you saw from Scott's email, the possibility of obsidian in Michigan is a recurring question.  I still haven't found any evidence of in situ obsidian from any sources, so I am hesitant to say it is from a deposit in Michigan.  Indeed, I believe it's more likely that the samples are glass slag.  

Glass slag is, basically, rough glass from an iron blast furnace, or glass making operation.  Much of it originated from England in the late 19th century and It is thought that manufacturers created slag glass by taking slag, the waste content of metal ores, from iron-smelting works and adding it to molten glass. The process created a variety of artistic effects so the product was often used in lamps, other glass work and jewelry when it was of good quality.  It can come in a variety of colors, including brown, green, blue, cream, and even purple.  When it was of less quality it was used for road and train track ballast, brick and mortar, and cement.  

It's possible the slag was placed in a load of track ballast because it was available, perhaps from one of the smelting operations in the U.P., or a glass making operation.  Just don't know.  However, as unlikely as this might be it is more probable, at least for now, than an unknown deposit of obsidian.

However, the bottom line is that both options are very possible.  Just because we haven't found an obsidian deposit yet doesn't mean it isn't there.  But I think it's more likely glass slag.

As for whether they are remnants of a meteorite impact, I don't think so.  Most are chondritic (look like stone) or metallic, or a combination.  Meteorites are not glassy like these.  See;

Your best bet is to take your samples to the Geology Department at Michigan Tech or to the A.E. Seaman museum.  They should be able to help with identifying your specimens.

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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