Of uncertain origin Desert Tropicals lists this is as probably a hybrid of Haworthia coarctata. It's reported that the rosettes can get from 1-1/2 to 2 inches around and stack to 6 inches high. It also offsets at the base.
     I picked up a couple small potfulls of these at Home Depot because it's an interesting looking plant. I put a few of them in potted arrangements with other succulents and will probably try one in the ground.