> Perlite and vermiculite are non-biodegradable minerals(?) which
> are mixed with potting media to provide better aeration. A
> visual inspection leads me to believe that vermiculite is
> derived from mica, but this is conjecture. Perlite, I've
> heard, is some sort of volcanic ash. I use perlite mixed
Vermiculite is a form of hygroscopic mica that occurs in large, long
metacrystals. Typically it has a lot of water in its matrix, and when a
large mass of it is heated, it explodes and yields long thin winding
wormlike (hence the term) stuff, that can be cleaved easily into what we
know as vermiculite. No, it's not biodegradable, any more than perlite is
(which is volcanic tufa expanded by heating--think of it as highly
processed granite), but it holds lots of water and I have to remember
that it may be OK to use it in carnivore soil but not cactus soil.
Sean Barry