i found this near a recent rock slide , it was interesting and different from everything around it and had been covered in dirt so it had just seen daylight recently after a very long dirt nap!
Short sand beach, Oregon
it passed the is it a bone test - porous / sticky
it’s hard and would be very difficult to break
it sounds like it’s got room for air inside
When I was cleaning it, there was a very waxy substance in some of the thin cracks. It has this horizontal line but it’s not like a crack or a scratch so maybe part of a turtle scute?
this round one is similar and was nearby if it means anything