No other info than a pic of it next to a writing pen?
It could be a naturally formed rock, it could be the bottom side
of an ancient oil lamp, it could be some type of fossil..
Help us out here..what is it made of? What does the other side
look like? Can you use a better camera than your phone, so the
pic is in focus?
People here are good at figuring out what things are, but they still
need basic info.