Silicon is a nonmetallic element in the carbon family. It is the second most abundant element in the earth's crust, at 27.7 percent, surpassed only by oxygen, at 49.2 percent.
Silicon is too reactive to be found in its pure form in nature, but it is contained in nearly all rocks as well as in sand, clays, and soils, combined either with oxygen as silica or with oxygen together with other elements as silicates. In the form of silicon dioxide, it also occurs naturally in plants and animals, including in humans, although it is still not clear what role it plays and whether it is essential. Silicon, should not be confused with silicone, which is a man-made polymer that contains silicon, oxygen, carbon and hydrogen.