Gilsonite (Uintahite)

Not coal. Not obsidian. A black, glasslike, shiny, soft asphaltite found only in Utah and W Colorado and used to make waterproof coatings, linoleum, etc. Because it is impervious to acids, it is used to line pipes and tanks used to store acid. Henry Ford used it to make shellack for his Model T's...which is why you could get it in any color, as long as it was black. 

From Bonanza, Utah. 

~2 inch pieces randomly picked $20.