We went sledding at my cousin's in-laws yesterday evening not far outside of Ann Arbor.

I noticed they had a nice collection of rocks, and mentioned it. My cousin's mother-in-law then pulled this out of a small bowl that was on a shelf.

She had it examined, and was told that it was about 8000 years old, and was used as a knife. Their son found it in their backyard several years ago. I should have put a coin next to it. It's about as long as my index finger.