May be hard to believe but Michigan has things stranger than the Monster clan... really.
One of them is the Petosky Stones, named for the city of Petosky where they're most abundant. Actually they can be found over most of the state because they were pushed around by the glaciers during various ice ages. They come is a variety of colors and surface textures but they have the hexagonal structure in common. Huh?
They all have that hexagonal structure because they all started out as rugose coral, about 350 million years ago. The coral's live gooey bits inside the stiffer, although not hard, structure, were replaces with minerals, fossilizing the coral into genuine rock. The infilling with minerals is why the variety of colors, depending on what minerals filled in. Sort of how petrified wood forms.
If you'd like a Petosky stone of your own, and can't convince Monster to run out and find one, and then polish it of course, just tell Google you want to buy one. I saw stones online, polished and raw, for as cheap as $17, and $25 for a piece 3-1/8" x 2-5/8"x 5/8" thick.
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