Silicon is one of the most abundant elements in the earth’s crust. As well as being used in carbon and stainless steel making in the form of ferro-silicon, it is the basis for most semiconductors, is used as silica in the production of glass and ceramics, and finds application as silicon metal in aluminium refining.
In steel refining, ferro-silicon (FeSi) acts as a deoxidiser to reduce carbon loss, but is also used to improve tensile strength and heat resisting qualities, and to enhance the magnetic properties of steels used in electrical equipment (see also electrical steels). In foundry iron production FeSi improves casting performance.
The most widely used grades contain 75% silicon, although lower grades are traded. Small amounts of aluminium and calcium are also present, normally 1-2%. And for more detail click and see wikipedia entry.