Looks like an adornment--a slate gorget and likely a specific type. Commonly found in the mid-west and extending into the eastern US if memory serves me correctly.
I am wondering about number one picture in the four above. The way the mark on the right side lines up with one on the left. Looks like a bit was started outside of hole the moved left into hole with to much angle causing it to hang up leaving marks directly across from each other. But I don’t know for sure.
It's either a boat stone, examples from Ohio, or a gorget examples from Kentucky. I'm leaning towards a gorget, Cherokee/Shawnee The gorget pic I'm looking at has 2 holes, the stone itself is 1 1/2 x 3 3/4
It appears to me to be a variation of an Indented Gorget
Here is an example from a search
The holes in the example posted dsmikle looks questionable in the hole area to me. I have found many broken and a few complete slate relics over the years. Most of the holes with stone drill exhibit conical holes. This example appears to have some sort of lip ridge area, which is often made from metal drill presses. The difference in the color of the holes also make me question the example.