If you look under Chemical Composition on this page, you can
find the types of rock that will be high in silicon. These are
what to look for when looking for quarry dust to add to your
compost, mulch, or manures.
http://en.wikipedia.org/wiki/Igneous_rock
(Most gumbos use a quart or two of water or stock, depending
on how much you are making. I noticed that recipe posted
above omitted it.)