I was just at a local Wal-Mart, where I found Old Castle sand- unfortunately "Multi-Purpose Playsand". But right next to it was this stuff called Garden Basics Playsand. Very white and fine, esp. compared to the Old Castle. Says "Screened and sterilized" on the bag, I believe it comes from Arkansas.
I bought a couple bags of each, and put the sand in a glass along with some cider vinegar (don't have white vinegar so that may invalidate this test). The Oldcastle sand went in and no sounds, just sat there. The Garden Basics sand, however, snap-crackle-and pop, it is in fact still sizzling a bit. The sand is still there-maybe some of it disolved, not sure...but is the test for a "good non-silica" sand if it crackles in vinegar, or does it actually need to dissolve?