I got this over 2 billion year old slab of polished stone at a silent auction last year. I was going to put it in a table surrounded by red Lyons sandstone, but thought the stone would show better without the distraction.
As noted in the caption. This is from a glacial erratic found in Kalamazoo County, Michigan.
Its mounted on a 1/4" thick slab of black plastic. You can use it as a hot plate, trivet, cheese plate or just put it out and show it off.
I just made it and its still available!