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!

Bill