Banded Slate?

[Mud Hawk]

If something gets naturally smoothed via erosion, please explain how the cleaved areas are still sharp and not rounded... sorry that just doesnt make sense. I do appreciate the input so dont get me wrong .

[KPT]

Rocks at the bottom of the Ice Age Glaciers were ground against bed stone which would create a similar object. As they slowly tumbled multiple sides would be abraded.

[Mud Hawk]

KPT, now that is a possibility I considered as there are glacial deposits that came down from Canada. The only thing that still has me wondering is that there is a second ground plane directly opposite of eachother and perfectly parallel. I think I am ready to let this one die at product glacial movement .

Hahaha I DID still want to know if it was banded slate though....

[KPT]

In my rock pile I have a stone which has 90 degree ground surfaces similar to yours.
30 years ago I saw a water driller hit a gas pocket at 150 feet down. The well blew water, mud, fir needles, maple seeds, fir bark, leaves and sticks all day long before dying down. One small stick about 1"x2" was ground on both ends. It was like sombody had held the stick against the pavement from a moving vehicle. The appearance was identicle to both of our stones.
This was the result of a glacial outwash flood at the southern tip of Puget Sound.