Silicon, semiconductor grade

Silicon is widely used in all kind of electronics, as well as in photovoltaic solar panes. The main material for silicon is one of the most abundant - sand. Sand needs to be quarried and cleaned - that produces lots of air pollution, mainly dust and particulate matters.
Next, the silica from sand (or quartz) is reduced to silicon, using carbon in various forms (coal, charcoal, coke, wood) and a lot of electricity, and finally, the raw silicon is refined to high purity levels, suitable for production of semiconductors and solar panels. That process requires energy, and various chemicals.

Main source: here.