What do you see that makes you think it isn't just natual? Serious question.
Can you circle and explain. I think just natural. Believe me I'm happy to be wrong, because I learn quicker.
Thanks
FWIW : Looks to me like a quarry blank of tabular (bedded) chert. About the right size and thickness.
You can't put a name on it until you have determined whether or not other pieces of the same chert can be picked up where it was found. If so, probably natural. If not, how far away from the find spot is the quarry
/weathering outcropping ? That's the determining issue re. whether it's an artifact (showing human modification of any sort) or not.
I found a quarry blank of similar shape a little while back. Out of context you would think it was natural. But it was made of a foreign type of rhyolite and was found surrounded by reduction flakes.
Other times I'll find rocks of local materials with no tool working signs nearby. Those are very likely naturally weathered.