Ground up pumice with a portland cement binder. Good insulation
qualities because of the porosity of the pumice. Very nice material for
building in at least some places.
Am I correct in thinking that it isn't especially good for building in
areas with winters below freezing and a fair amount of humidity because
of the possibility or probability of cracking or exfoliation (caused by
expansion of ice upon freezing)? There seems to be a fair amount of
information around on the subject of pumice-crete, but nothing that
addresses this particular question. It's pretty obvious that the stuff
ISN'T often used in the eastern US, but I wonder if it's really a matter
of not being an appropriate building material.