Silicon
Silicon is a very common element -- for example, it is the main element in sand and quartz. Carbon, silicon and germanium (which, like silicon, is also a semiconductor) have a unique property in their electron structure -- each has four electrons in its outer orbital. . The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In silicon, the crystalline form is a silvery, metallic-looking substance. While silicon crystals look metallic, they are not, in fact, metals. All of the outer electrons in a silicon crystal are involved in perfect covalent bonds, so they can't move around. A pure silicon crystal is nearly an insulator that is why we must add impurities to the material to get the right electronic properties.