We 
Hydroponics
The next growing media we're talking about is
PUMICE
...Pumice is a mined mineral just like perlite and is formed by a super-heated
and highly pressured volcano.
It can be white, pale gray or pale yellow, depending on the area's minerals. But usually, pumice is darker than perlite.
This is a lightweight stone, which is porous, slow to break down and holds the air 
well because of spaces between each particle. This makes the medium tend to float on water, but not to the extent of perlite.
Pumice has good water retention, 
but not as good as vermiculite, which is also a mined mineral...
Benefits 
Lightweight Excellent air holding capacity
Downsides 
Lightweight for some hydroponic system