Many compounds that contain boron are highly flammable, but the free element is not found in the natural world in a pure form. Most often, the element is found as the compound borax. Most boron compounds that feature hydrogen are very flammable.
Boron is found in a variety of forms in the natural world. Humans use boric acid, one of the most common naturally occurring forms of boron, as a pesticide. Other forms of boron include crystalline compounds. Boron is an important element involved in the splitting of prokaryotic cells. Additionally, plants require substantial amounts of boron for proper growth and health.
Boron naturally occurs in human water and food sources, but it is not considered a dietary requirement. The human body usually contains less than one part per million of the substance. Ingesting more than 20 grams of boron may be life threatening. Some scientists suspect that boron deficiencies may play a role in arthritis among young adults. Other scientists are researching the effects of medicinal boron in the treatment of the disease.
One compound containing boron, called boron trifluoride etherate, is not only flammable but may explode on contact with air. When placed in water, the compound causes an exothermic reaction and releases other flammable compounds.