Daily price prediction thread, page-6546

https://semi engineering.com/from-sand-to-wafers/#:~:text=Ultrapure%20silicon%20is%20also%20used,made%20of%20high%20purity%20silicon.

Found it,  "The starting material really is sand. Not just any sand, but silica sand, specially quarried for this purpose and having concentrations of quartz (silicon dioxide) as high as 95%.
Purification starts by heating the sand with a reducing agent, carbon, to produce carbon monoxide and silicon. The product of this process, known as metallurgical grade silicon (MG-Si), may be as much as 99% pure. Additional processing is completed until ultrapure electronic grade silicon (EG-Si) is obtained."