Granite from the Plane of Earth is the softest, smoothest brand of granite found anywhere in game, for only Plane of Earth Brand Granite (tm) is powdered in a MIXING BOWL instead of a Mortar and Pestle. Buy yours today!
Took me a good 45 minutes of running around trying 1-6 granite, forges, brew barrels, JC kits, etc until I found a working recipe. OH - Also, each success makes FOUR powdered granite.
(Correction sent, bug report sent ...)