Elemental boron is a light element with several forms that differ in the way the atoms are packed, none occurring in nature. The element is most familiar in compounds used to make fiberglass, heat-resistant borosilicate glass, and cleaning products. But its most important role on Earth is as an essential micronutrient for plants. Besides glassware and cleaning products, boron and its compounds have been used in semiconductors, fire retardants, cancer treatment, high-energy fuel, cosmetics, adhesives, pesticides, wood preservatives, and the leather tanning industry. Readers learn about borates and boranes, among other boron compounds, and about covalent bonding.