Thanks. I think there is confusion here as South Africa might not even produce it. We would not have any notable deposit of obsidian to use and we already are one of, if not the, highest producer of vermiculite in the world.
I did find styrofoam in the bottom of orchid pots but oddly I was not so bothered by that as it does make sense given the air nature of their roots. On the other hand it bothers me that they use it in potting soil mixes, which by the way do not list ingredients as they do not have to.
Oh well, thanks. I know we import or make some perlite so I am going to buy it for use over seeds when I germinate. That soil will make it into the final mix for pots anyway when I pot up but I definitely won't be able to mix large quantities of perlite and peat for my large pots. (We also import the peat)
I will be trying vermiculite in the near future as a lightening agent although I have always been bothered by the fact that vermiculite breaks down into other clays and that it is a clay itself. Maybe because I have clay soil and I have a horror of clay. (Don't worry, this is for pots, I'm not adding it to clay soil).