ALUMINUM

also spelled Aluminium (Al), chemical element, a lightweight, silvery-white metal of main Group IIIa (boron group) of the periodic table. Aluminum is the most abundant metallic element in the Earth's crust and the most widely used nonferrous metal. Because of its chemical activity, aluminum never occurs in the metallic form in nature, but its compounds are present to a greater or lesser extent in almost all rocks, vegetation, and animals. Aluminum is concentrated in the outer 10 miles (16 km) of the Earth's crust, of which it constitutes about 8 percent by weight; it is exceeded in amount only by oxygen and silicon.