Thumler's Model B polishing a large rock

My Mom bought this rock for 10 cents when I was 5 years old. (45 years ago) I've had it sitting around forever and figured I'd break out the Thumlers Model B and tumble it to see if the tumbler could hold up to a rock this large. It did. Pretty sure this rock is a chunk of Quartz https://rocktumbler.com/thumlers/mode...