What kind of rock is this?

[grouse11]

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.

[Pat B]

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.

[Piratkey]

look like glass  

[grouse11]

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.

[Jon Stewart]

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.

[sleepyhollow]

Slag glass is what I was thinking

[Izzy]

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.

[Sharpend60]

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.

[bamboo]

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

[Phrogdrvr]

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

[SKITCH]

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

[Jerry Jeffer]

Looks like kryptonite!