Boron (IPA: /ˈbɔːrɒn/) is a chemical element with atomic number 5 and the chemical symbol B. A trivalent metalloid element, boron occurs abundantly in the ore borax. Boron is never found free in nature.
Several allotropes of boron exist; amorphous boron is a brown powder, though crystalline boron is black, hard (9.3 on Mohs' scale), and a weak conductor at room temperature.
Elemental boron is used as a dopant in the semiconductor industry, while boron compounds play important roles as light structural materials, nontoxic insecticides and preservatives, and reagents for chemical synthesis.
Boron is an essential plant nutrient, although soil concentrations of > 200 ppm can cause marginal necrosis in leaves, and as an ultratrace mineral is necessary for the optimal health of animals, though its physiological role in animals is poorly understood.