We were cleaning up some scrap metal on a farm today and I came across a bunch of these boulders. They have a greenish tint and are pretty translucent. The surface is much like glass.



I was thinking it may be obsidian but am not. I have never attempted any knapping but thought maybe I would give it a try if the material will work because I have an almost infinite supply.

Here are some pieces that I broke off.



Here is the translucency.



Thanks for all the help.

Looks almost like obsidian but it couls also be dasite. It looks like it should knapp well. I wonder if it could be slag glass. I don't think there is any obsidian in PA unless it was brought in and I don't know where dasite comes from.

look like glass  

Thanks for the replies. with a little more research, I found that PA has no natural obsidian. The boulders were about twice as big as a basketball. I am just gonna teach myself to knap with it and hope I come out with something that looks like point.

By the looks of the chunks you have laying there what ever rock/glass it is, it looks freeze fractured. Dacite and obsidian comes from the western portion of the United States.

I am sure it will knap so give it a try. Go to youtube for flintknapping and they will show you how to make your tools and flintknap.

Slag glass is what I was thinking

I found glass of many different colors in similar form in Pike county PA (Matamoras) on the Delaware River. There was a glass factory there back in the day.

Slag.

I live near an old rail way it is all over.
I have also found very similar stuff near an old pig iron factory.

slag----as a kid we lived by an old iron funace--there were piles of it in colors ranging from sky blue to green and almost black--all depends on the impurities in the local ore
that piece might be knappable??--some is full of bubbles

We live by a 200 yr old iron furnace here in PA.  We can still find that old slag glass in the creek down stream.  I guess, when you think about it, it's probably not that much different from obsidian.

Tom

Would you expect to find this kind of stuff around an old steel mill or glass plant???

Looks like kryptonite!