Off the top of my head, I've tried: Many cherts (Ft. Payne, Knox, Dover, Flint River, Coastal Plains, Pedernales, Georgetown, Edwards Plateau, Flint Ridge, burlington, Belize, Horse Creek, onondaga, Boyles, cobden, etc.) Kentucky and Indiana hornstones, English flint, rhyolite, obsidian, dacite, basalt, silicified metasiltstone, quartz, quartzite, silicious limestone, argillite, coral, opal, opalized phosphate, agate, petrified wood, Mookite, jasper, Fenton glass, slag glass, beer bottles, forty-oz. malt liquor bottles, plate glass, TV tube glass, principal's-office-door glass, toilet tanks, porcelain sinks, coffee cups, ashtrays, plates/saucers, insulators off electric poles, ice, and probably other wierd stuff I can't remember. Out of all that, my favorites are probably hornstone, Flint River chert, Fort Payne chert, and good rhyolite.
