Having heard good things about pumice on this list,
I went to our OSH and purchased a small bag of Black Gold brand pumice.
It was about 10 times heavier than I expected pumice to be, but they
assured me that was just because it was wet.
At home, I noticed it had a lot of dust, which I did not think I wanted in
my growing medium
(not having read the note from Jane yet about the dust containing useful
minerals).
When I washed the pumice, I noticed it sank. I expected pumice to float.
The pumice in Baja California floats and resembles styrofoam.
I wrote to Black Gold and they replied

"The Black Gold Pumice that you bought comes from a source in central
Oregon,
the same source we have used for a long time. Chances are that you will
get the
same type of pumice in California, Oregon and Washington, if you buy Black
Gold.
This is a denser pumice, but should not affect the porosity you are
seeking.
The dust comes from the pumice rubbing against itself in the packaging as
it is moved around."

I also noticed when I washed it that I could sieve out the sizes to get
pebbles for topping and
grit to sand size for growing medium and could wash away the silt-sized
sediment.

- Gastil
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