Boron

Boron is a chemical element with atomic number 5 and the chemical symbol B. Boron is a trivalent nonmetallic element which occurs abundantly in the evaporite ores borax and ulexite. Boron is never found as a free element 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 > 1.0 ppm can cause marginal and tip necrosis in leaves as well as poor overall growth performance. Levels as low as 0.8 ppm can cause these same symptoms to appear in plants particularly sensitive to boron in the soil. Nearly all plants, even those somewhat tolerant of boron in the soil, will show at least some symptoms of boron toxicity when boron in the soil is greater than 1.8 ppm. When boron in the soil exceeds 2.0 ppm, few plants will perform well. Plants sensitive to boron in the soil may not survive. When boron levels in plant tissue exceed 200 ppm symptoms of boron toxicity are likely to appear. As an ultratrace element, boron is necessary for the optimal health of animals, though its physiological role in animals is poorly understood.