Stone Candle Holder

Stone Candle Holder

My parents just got back from a trip to Arizona, and the Grand Canyon. They brought me back this stone candle holder. I find the different layers incredibly interesting, but I’m wondering what all the dark lines between the different sections/top could be-they are slight ridges that stick out of the side of the holder. Also, I wonder how cylinder was formed- would a rock corer form a sample that could be shaped into this holder? Or could a corer disintegrate the rock into little pieces?