Silicon. Lump of silicon, a chemical element with the symbol Si. It is a semi-metallic element, and belongs to group 14 of the periodic table. It has an atomic number of 14 and an atomic weight of 28.086. It melts at 1410 degrees Celsius. Silicon is used in the semiconductor materials found in solid-state electronic components like microchips and transistors. It is the second most abundant element in the Earth's crust, most commonly found combined with oxygen as the silicon dioxide (SiO2) found in rocks and sand. In this form, it is used in the manufacture of glass.