AboutC. 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 24 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
Question I was gardening in my yard and just below the surface I found what appear to be lava rocks. Now, I live in a suburb on the southeast side of Cleveland, Ohio, around ten miles from Lake Erie. The area in which I live has been developed for around ninety years. The lot on which my house stands was one of the last to be built upon around 45 years ago. I found what looks to be, after Internet research and looking over photos on those sites, lava rock. One of the rocks is jet black and looks like glass. It is very, very hard. While it looks like glass, it does not shatter like glass. I know this because one end of it is very thin, wafer thin. I dropped it and nothing happened. It didn't break. The other rocks are a grayish blue color and have what looks like places where bubbles popped. Inside of a few of these spots is shiny and black and contain what appear to be the same substance the solid black shine rock is made of.
So, I was wondering if it is pretty common to find these in this area and so close to the surface. I had dug down around four inches. The one shine black one was just sitting on top on the ground. I have found thin layers of coal not that far down, around two or three inches. So, I had considered that the solid black one is fossilized coal. What do you think? Is it common?
Answer Hi Ramona,
Your description, jet black, glassy, and hard, could be a couple of things. I would first suspect obsidian, another name for volcanic glass. But it isn't common in your part of the country. Native Americans did trade for it in Michigan to use for arrow heads and such. They traded the copper we have here. Michigan copper was found in archeological digs as far away as New Mexico. But it would be very rare. Can you see through any part of it? Especially the very thinnest parts. You should be able to see through it, even if it's distorted, if it was osidian. Think about stained glass.
If you can't I think you have a bit of coal of the type; anthracite. It can look pretty much like obsidian and exactly as you describe; shiney, black, and hard. Since there has been coal mining all around your area (Pennsylvania, Virginia, Kentucky) it is likely that veins run all over. It is also likely that some was transported here and there and perhaps some spilled at what is now the present location of your house. All things considered I'll say you have a bit of anthracite.
