Funny enough, in a Central/South Western region of Bolivia while on a hiking excursion, I came across what looked to be a very old (looked late Inca/ early colonial period, definitely post-ceramic) habitation site....it had a huge piece of stone that looked glass smooth from it being rubbed on and flat as a table. The entire area, now at 3000+ ft of elevation used to be shoreline to the Pacific ocean prior to the last ice age. When the Andes rose upwards, they forced up with them literally hundreds of thousands of square miles of sedimentary rock (complete with intact dinosaurs tracks, fossilized plants and whole prehistoric giant turtle remains). Turns out this sedimentary rock begins to break down with water and the local natives have been using certain layers or strata to sharpen stone, bone and metal implements since forever (although I assume steel was introduced by the Spanish as I don't think one can build a blade from pure gold or raw iron).
So my guess would be that there are indeed treasure troves of natural stones of all types (sedimentary, quartz/novaculite, slate, etc etc) all over the globe waiting to be discovered.
Maybe I could pay them a visit the next time we drive back home to visit family.
