Hi! Ian, To know, you need to get it tested. Some granites are better than some basalt, but generally basalt is higher.
On my farm, my granites are higher than most basalts, but my amphibalites (basalt like) are very high. For potting mix, you may need to sieve twice. Insect screen, as fitted to house windows in Australia is about 14 meshes to the inch and takes the large portion out and a flour sieve from the kitchen department of your Super Market will take the too fine portion. The fine portion will contain down to clay like particles and is useful in the compost heap, but too fine for potting mix. The coarse portion is useful to put on top of light, surface planted seed to hold it in place while germinating. Larger still portions are goof for "crock" on the bottom of the pot, if highly paramagnetic. See the story in the January Acres USA. If doing large amounts, the sieve may need upgrading to screens and industrial mesh screens are readily available from industrial engineering suppliers, if you don't mind paying a lot of money. I have several screen about two feet by four feet, set up on legs and sloping steeply, great to shovel through. Gil Allan Balliett wrote: > I'm going a little nutty right now, trying to learn a jargon so I can > speak with people who are quite a drive from me and who really don't > have the time to spoon feed the ignorant. > > I'm looking to buy a few yards of 'crushed gravel sand' to use in a > potting mix formulation recommended by Heinz Grotzke in "Biodynamic > Greenhouse Management." > > So far, I've been offered trap dust and 1/4inch (and lower) stuff > from a realatively close-by quarry. If I can communicate screen size, > I think I can buy what I need. > > AND, I would assume that it's cool to take basalt instead of granite, eh? > > Which is to say that I've found a source for basalt trap dust down > here. My recollection is that it tests very highly on the Callahan > scale (paramagnetics), but I'll have to have it tested again. > > Thanks > > _Allan
