From Quartz to Chip-Grade Silicon: Three Purity Jumps, Not One
Silicon goes through a carbothermic smelt, then a chemical vapour purification, each step removing impurities the previous one could not touch.
Quartz mining itself is conventional quarrying, covered on this material’s geology page. Turning that quartz into the silicon grades covered on this material’s materials science page takes two further, genuinely distinct chemical processes.
Step one: carbothermic reduction
Quartz (SiO2) is reduced with carbon in an electric arc furnace at extreme temperature:
Step two: the Siemens process, for electronic grade
Metallurgical silicon is nowhere near pure enough for a semiconductor. It is converted to trichlorosilane gas, distilled repeatedly to strip trace impurities, then deposited back onto a pure silicon rod in a process called the Siemens process, reaching purities of 99.9999% or higher, covered on the materials science page for why this level of purity actually matters electronically.
Why polysilicon for solar is a separate, intermediate grade
Solar-grade polysilicon sits between metallurgical and full electronic grade, purer than metallurgical silicon but not requiring the extreme purity a microchip does, a real, distinct product tier that has become the largest single silicon end use by volume, covered on the application-wise page.
Sources: carbothermic reduction and Siemens process chemistry draw on standard extractive metallurgy and semiconductor materials references (USGS); production figures reference the production data elsewhere on this site.