Huge rock from Montana Help ID please

[Sommer]

My grandmother who is 87 inherited this rock from her mother. It was found high in the Montana mountains. It was an engagement gift to her from a gentleman that climbed high in the mountains and brought it back to her. We were curious what it might be.  It weighs over 50 pounds. Any ideas? Thanks!  

[adam]

It is man made- not natural

[d_day]

That looks to me to be a large and stunning piece of man made glass.

[Sommer]

Thanks so much.  My grandmother’s mother was gifted it from a gentleman that claims he got it from high in the Montana mountains.  This was over a hundred years ago. So I have no idea where it came from.  Thanks for your replies. 

[clay]

It is indeed man made glass. It could be from a glass foundry but more commonly these large pieces are from commercial metal smelting operations. The silica sand used in the smelt are skimmed off the hot melt and discarded as large glass blobs. As the glass cools it tends to shatter. The white balls you see in the glass are spherulites formed from the slow cooling of the large mass of glass.

It could have been found near a smelting operation in Montana or a lead smelting operation in Missouri. It all looks very much alike after they have cooled.

[Sommer]

Clay, Thank you so very much. It’s been a mystery in our family for years. I greatly appreciate the help. Your explanation was awesome.