Ding Ding Ding.... I was actually looking for a specific name, but we are going to give it to Pat. It is Navajo Sandstone, or some call it Jurassic Navajo Sandstone. They are actually unsure if it is from the late Triassic or early Jurassic period. It is the same sandstone that makes up Arches National Park, Canyonlands National Park, Capitol Reef National Park, Zion National Park, Grand Staircase-Escalante National Monument, Dinosaur National Monument, Colorado National Monument, the sandstone around Lake Powell, and lots of others. There are quite a few specimens around with dinosaur tracks in them, so I do believe they have been around a while. It also comes in white, pink, grey, brown and multicolor.This particular piece has been used as a grinding stone for grinding horn down and as an abrader for knapping. I have some bigger pieces that can be left stationary and rubbing your bow on for grinding/sanding. They also work well as sharpeners for axes and hatchets. Justin