I was actually surprised to find the density of Limestone & 6061 Al are that close. The problem (or at least one) is that stone isn’t nearly as strong as Al. It’s not possible to make a durable throw of stone the same thickness as one of Al. That’s not to say a decent yoyo can’t be made from the material, though (especially using 3D printing like Andy).
You wouldn’t believe it! My wife gave me my Valentine’s Day present early and it’s a stone frickin yoyo. She bought it from a crystal girl. It’s kinda nuts. It’s 30 mm width 48 mm diameter but weighs 113 grams. As far as yo-yos go it’s definitely prehistoric in nature, super thick axle, can’t do any tricks with it but it will indeed go up and down if I crank string tension and it’s very beautiful. 2/10 yoyo 12/10 thoughtful gift.