Flint-hard, brittle, non-porous it proved to be a desirable potting medium but in small piles, in the north of Australia where rain is lacking for six months; especially good for Encyclia cordigera (atropurpurea) Brassavola nodosa, Dend. aggregatum, D. superbiens, D. discolor, D. lineale, etc., possibly because the nightly copious dew formed a water-film on the glass-like surface. AU80-229