Pronounced is a chemical element with atomic
number 5 and the chemical symbol B. Boron is a trivalent metalloid element which
occurs abundantly in the evaporite ores borax and ulexite. Boron is never found
as a free element on Earth.
Several allotropes of boron exist; amorphous boron is a brown powder, though crystalline boron is black, extremely hard (9.3 on Mohs' scale), and a weak conductor at room temperature (22-28 °C, 72-82 °F). 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 high soil concentrations of boron may also be toxic to plants. As an ultratrace element, boron is necessary for the optimal health of rats and presumably other mammals, though its physiological role in animals is poorly understood.