I started with a simple 4-port usb hub my sister got on clearance someplace. I think she paid a dollar for it. As with all things, the first step is to take it apart - in this case, simply remove the plastic housing. Stripped down in this way, It's much easier to fit the thing with a marble housing.
Next, I picked a piece of scrap marble we salvaged from a local tile store. It doesn't take much stone to enclose a small usb hub.
Next I used a tabletop tile saw to cut the stone and carve out space for the hub"s circuitry. I used my sister's MK-101 wet tile saw primarily because it's really loud, and it's purple.
Once the pieces were cut, I assembled them around the hub, gluing them together with Devcon 5-minute epoxy.
Finally, I lined the bottom of the hub with white felt, to protect my sister's dining room table.
The hub works perfectly. It doesn't slide around, looks great, and when you plug it in, you can see the green glow of the LED power light through the marble..... very cool.