Puuva is a soft blue-black stone, very porous. It is often found near volcanoes. Some scholars maintain that puuva is created from the interaction of lava and the Mysterious Blue, though alchemists and koldun haven't quite discovered what it is good for (if anything).
Since it is only found on those Cloud-Islands that have volcanoes, it is a valuable trade item.
However, since puuva is so soft and porous, it is rarely used for anything practical. The most common puuva uses are as expensive knickknacks or ingredients in patent medicines.