Pumice
Jane McGary (Fri, 15 Oct 2004 17:26:20 PDT)
Rodger Whitlock wrote,
Everybody interested in pumice should be aware that the stuff sold
for landscaping is not necessarily pumice. I have several bags each
of black and red "volcanic cinders"; these are not pumice, but
others might mistake them for pumice because of their volcanic
origin.
Volcanic cinders (for which there is undoubtedly a technical term)
are little blobs of lava that were thrown into the air and hardened
before landing. They are dark, have sharp edges, and are definitely
not "frothy".
the technical term for this material is "scoria." Loren Russell, an
excellent rock gardener, swears by what is locally called "red rock" (red
scoria, loosely red pumice) as a nutrient-rich material, and incorporates
the dust and fines from piles of it (which are sold as a mulch) in his
planting mixes.
Jane McGary
Northwestern Oregon, USA