What is with the stone-throwing, anyway? Besides the fact that anyone who threw a stone to inflict harm or damage in my neck-of-the-woods would be arrested, if I walked outside right now, I wouldn't be able to find one to throw. What these people need is a decent DPW to pick up and crush the darned things.
All depends on where you live. Where I live now there's considerable chunks of limestone around. At my grandparents farm there was a huge pile of glacially smoothed stones which would pop up from time to time. Some of those were flint, some were mineral rocks of some kind, probably quartz or near relatives of it. Thee latter could be quiet pretty on the inside. OTOH, my wife's grandparents farm was pretty much stone free, because after those glaciers went by, there was tens of feet of windblown soil deposited over the top of what the glaciers left behind.
And in that part of the world, they may still use stones for paving material, at least the under layer, which would still leave lots of them lying about.