You say, "They don't use silica sand to make semiconductors, they use quartzite." Even if this were true, quartzite is just silica sand that has been sintered together (naturally, underground). Moreover, Vince Beiser's Wired article (linked above) claims that in fact both high-purity silica sand and lump quartz (probably, as you say, quartzite) are used as sources of silicon.