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Identity Helpobsidian in New England? Again? Please help identify

9th Nov 2018 03:46 UTCCarl Andersen

Ok I’ve seen this question posted on here before. I think I might have found obsidian in Connecticut. It’s definitely not coal or any sort of slag. I work in a stone yard that breaks up various types of granite and field stones, and whatever else comes to us. We also put many of our stones through saws. Every once and a while I see different odd igneous rocks. This stone, which I will provide a picture definitely has the appearance of glass. On the underside of it is where it was cut with one of our saws the stone itself was originally round and it’s been broken revealing an obsidian like appearance. Just not jet black. When it’s wet. It looks very dark. Now I took this stone home for aesthetic reasons and decided to put urethane on the broken side of it, so now it has the permanent appearance of being wet. Please help in identifying. Possibly many more I identified stones to come.

9th Nov 2018 04:52 UTCDoug Daniels

The second photo sure suggests obsidian. If it is, pretty sure isn't from Connecticut.

9th Nov 2018 05:56 UTCCarl Andersen

As I said, the second photo is the part that’s got a coat of polyurethane, it’s not actually that jet black color. I understand that not all obsidian is jet black too. But anyways, all the stone we get shipped into our yard comes from the area. All local to new england

9th Nov 2018 06:42 UTCKevin Hean

The fracture looks more like micro crystalline to me not obsidian.

9th Nov 2018 07:45 UTCCarl Andersen

If you could maybe elaborate on the micro crystalline? I’m going to try to attach a closer photo. Within the second photo you can see a triangle where the polyurethane did not touch the stone. It has a more matte black look than it does gloss. Hope that helps

9th Nov 2018 08:50 UTCKevin Hean

The fractures including the small chips on the bottom photo, don't look like typical fractures of glass, look more like a fine micro crystalline quartz similar to jasper or agate. Not saying it is one of these two.

9th Nov 2018 12:00 UTCReiner Mielke Expert

I can see bubbles in it. Seems to me it is a glassy slag.

9th Nov 2018 12:13 UTCKeith Compton 🌟 Manager

I think its man-made

Fractures (if that's what they are) do not appear to be consistent for obsidian.

9th Nov 2018 13:04 UTCLarry Maltby Expert

Another possibility is that it may be a stash of obsidian from the western states transported by Native Americans. One piece looks like an artifact. The others could be material for future artifacts. Does the area have an archaeological history? What about the possibility of a stash left by another rockbound? One hundred years from now someone digging around my house will be surprised what he or she finds.

Were they found close together? On the bank of the Thunder Bay River in Alpena, Michigan a group of copper artifacts mixed with natural copper specimens was found. It was thought to be the contents of a skin bag that had rotted away.

9th Nov 2018 14:31 UTCCarl Andersen

All the pictures you see are of one stone

9th Nov 2018 14:36 UTCCarl Andersen

I’m not so sure you’re seeing it correctly. Those don’t seem to be bubbles of any kind. This piece is heavy and the toughness has got to be pretty high up there on the scale but I could be wrong

9th Nov 2018 14:45 UTCCarl Andersen

Thank you all for the help. I’m guessing slag. Looks like a lot of signs are pointing towards it being slag. I just didn’t want to believe it. The piece is so heavy and reminds me of actual glass in no way. I didn’t exactly think obsidian either. Please keep in mind that this piece is also naturally a matte black color. The glossy sheen is something I applied to the rock/slag itself

9th Nov 2018 14:58 UTCBob Harman

So CARL, from your photos of the one example you have several possibilities.

It could be something like dark slag glass or similar man made stuff as KEITH and REINER suggest.

It could be dark obsidian (volcanic glass) as you believe and DOUG seemed to agree with. If so, it certainly is not native to Connecticut and might be imported either by accident or part of an old stash as LARRY M suggested.

Or it could be dark microcrystalline quartz, like a chalcedony, chert, flint etc as also suggested.

I favor this last thought as your last photo closeup of the recently fractured surface shows a rougher texture than the usual freshly fractured surface of obsidian which, to me, is usually very smooth and very glassy. Also you sprayed it, darkening its color and making it more lustrous than natural. So, its natural color and texture would be matte, dark gray, as a chert or flint nodule might be.

However, we may not be able to be more definitive than that from your photos. CHEERS.....BOB

9th Nov 2018 16:49 UTCDonald B Peck Expert

Carl, I am inclined to agree with Bob. It is not smooth and lustrous enough to be glass and your last photo seemingly has an almost fibrous texture to it. Where in Connecticut did you find it?

9th Nov 2018 17:31 UTCCarl Andersen

Thank you Donald. It came from my job, a stone yard in northeastern Connecticut. But the stone we receive there comes from various places throughout Connecticut and Massachusetts

9th Nov 2018 17:33 UTCCarl Andersen

And thank you all for the help. I’m quite the amateur when it comes to a lot of stone and mineral knowledge. My spouse collects various small crystals, but that’s about as far as my knowledge goes. It does not mean that I’m not fascinated by the study of rocks. I hope to learn much from this forum

9th Nov 2018 17:36 UTCReiner Mielke Expert

Slag does not have to be "glassy". It can have the texture and luster of black chert, agate, cryptocrystalline quartz or glass. Have you checked it with a magnet to see if it is magnetic? Also you need to test the hardness and specific gravity before you can even begin to identify it.

9th Nov 2018 23:23 UTCA. M.

To me it's look like man-made - like a ceramic or concrete product, with half is covered with black paint/enamel - ?

10th Nov 2018 16:19 UTCMark Heintzelman 🌟 Expert

I would certainly agree it looks like slag. As Reiner notes, not all slag is purely glassy looking in the conventional sense. Here is a large sample I have of such a cherty appearing slag. Sadly it is a found object and not from a particular facility, so I don't know what process it is the result of, but a Neodymium magnet does stick to it.

10th Nov 2018 17:14 UTCReiner Mielke Expert

One other thing about slag. It can look like rock and does not always have bubbles in it. One of these days I am going to take a suite of photos of just slag and post them so people will know how it can look. The variation is amazing.

10th Nov 2018 18:04 UTCPaul Brandes 🌟 Manager

That would make a fabulous Mindat article with photos, Reiner.

12th Nov 2018 22:22 UTCEd Clopton 🌟 Expert

This inquiory sounds more or less settled, but I don't think anyone has mentioned this rule-of-thumb test yet: obsidian tends to have a relatively low density, so if the specimen in question is conspicuously dense, that argues against it being obsidian.

13th Nov 2018 14:45 UTCHarold Moritz 🌟 Expert

Being a Connecticut geologist and collector, I have to chime in that there is no rhyolitic rock formation in Connecticut or really anywhere in New England that would produce such a stone. Although there is plenty of basalt, which did have tachylite glass, it has mostly devitrified due to its 200 million year age, and the glass was in tiny globules. I qualify the statements because there is some tachylite from the Cinque Quarry in East Haven (https://www.mindat.org/loc-6789.html), but the samples are not very glassy or as large as the piece in question, and are from south-central Conn.

But there is plenty of glass slag from all sorts of industrial processes, old and modern, and these turn up all the time. The piece in question was not found in-situ, so where it is from originally, who knows.

4th Sep 2021 21:37 UTCPaul Brandes 🌟 Manager

The only known BIF in New England is in Vermont at Diamond Hill. This is also no known BIF on the Avalon Terrain; this is not BIF.

Thread is closed.

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