El silicio (del latín: sílex) es un elemento químico metaloide, número atómico 14 y situado en el grupo 14 de la tabla periódica de los elementos de símbolo Si. Es el segundo elemento más abundante en la corteza terrestre (27,7 % en peso) después del oxígeno. Se presenta en forma amorfa y cristalizada; el primero es un polvo parduzco, más activo que la variante cristalina, que se presenta en octaedros de color azul grisáceo y brillo metálico.

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Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a blue-gray metallic luster, it is a tetravalent metalloid. It is a member of group 14 in the periodic table, along with carbon above it and germanium, tin, lead, and flerovium below. It is rather unreactive, though less so than germanium, and has great chemical affinity for oxygen; as such, it was first prepared and characterized in pure form only in 1823 by Jöns Jakob Berzelius. Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earth's crust. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals. Such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with silica sand and gravel to make concrete for walkways, foundations, and roads. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass and many other specialty glasses. Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has a large impact on the modern world economy. Most free silicon is used in the steel refining, aluminium-casting, and fine chemical industries (often to make fumed silica). Even more visibly, the relatively small portion of very highly purified silicon used in semiconductor electronics (< 10%) is essential to integrated circuits — most computers, cell phones, and modern technology depend on it. Silicon is the basis of the widely used synthetic polymers called silicones. Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, secrete skeletal structures made of silica. Silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses.

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