You can heat up some rocks with carbon to get silicon and CO2, then use the Czochralski method invented in 1915 to produce a single giant crystal by essentially dipping a stick into molten silicon and slowly pulling it out. Then you can slice up that big crystal into wafers.

There’s a cool photo on Wikipedia of somebody just growing a crystal: https://commons.m.wikimedia.org/wiki/File:Silicon_grown_by_C...

There’s a bit of waste, but AFAIK it’s not too bad compared to other things.