@pyrate @Aether @Marakus @sapphire I would expect the right beach or alluvial sands to be quite pure actually, from a mineralogical point of view. Not to get into a geology lecture but it has to do with what minerals persist well in surface conditions and which tend to be weathered into other things, and quartz -- SiO2 -- is extremely persistent.

Now if they're mining hydrothermal quartz veins or something maybe that's even better. But that's also fucking crazy unless it's waste rock from mining other things, which it could be, because hydrothermal quartz is associated with precious metal bearing sulphides.