A chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid and semiconductor. It is a member of Group 14 in the periodic table: carbon is above it; and germanium, tin, and lead are below it. It is relatively unreactive. Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was able to prepare it in pure form. Its most common compound, silicon dioxide, or silica, occurs in nature as quartz, as well as in various living organisms. As a semiconductor, it is widely used in transistors, solar cells, and integrated circuits.