I have 40 pounds of Drystall as well as white pumice bought from a nursery.
When I put it into a bowl of water it sinks. If you look at Drystall and
pumice under microscope, they are identical.
Your data point on Crater Lake is interesting, and I don't know why your
pumice behaves differently than mine. If I read the pumice raft idea
correctly, this just means that sometimes a large piece of pumice traps a
large air pocket internally.
Perlite, however, is a significant floater.
Sorry for top posting but I could not get my reader to quote your post
"Chris" < firstname.lastname@example.org> wrote in message
Click to see the full signature.