Boron
The only nonmetallic element in group 13, boron has a strong tendency to covalent bonding. It's lonely complex structural chemistry arises from the (2s)2(2p)1 configuration, which produce it one less valence electron than the number of orbitals in the valence shell. Simple compounds such as BCl3 have an incomplete octet and are strong Lewis acids, but boron usually accommodates its electron deficiency by forming clusters with multicenter bonding.
Boron is not a common element on the Earth overall (about 9 p.p.m. in the crust) but happens in concentrated deposits of borate minerals such as borax Na2[B4O5(OH)4].8H2O, associated with former volcanic activity or hot springs. It is used mostly as borates in enamels, glasses, detergents and cosmetics, and in lesser amounts in metallurgy.