Sorry, just a naturally formed stone. If it had been used to dig with the end would have been highly polished from use wear.
Take a look at this example. This is a Stone Hoe that was used to dig fields for planting. You can see the polish from use on the bit end. The stone this is made from is very heavy and dense, so you know it took a long time to get that amount of use wear on that edge. Your piece looks to be sandstone or another softer stone so if it had been used it would have shown lots of use polish and it doesn't. I'm positive it is just a cool natural stone.
PS. Please, please, please!! No one say a Moccasin Last, okay. Thanks. lol