A sling shot should just about do it, maybe throw in a couple of punches and he’ll be down. He only needs cooked fish meat and then give it about 10-15 minutes and then you’ll have your own rock elemental
Wiki says: To tame it, you need brute force like a rock straight into its head.
Billy (tribe of billy) - lvl 2: Will my Journeyman slingshot work? I just spawned here and i was told it eats rocks! I have some in my pocket! I WILL TAME IT