The most abundant metal, and the third most abundant element, aluminum makes up about 8% of the Earth's crust by weight. Aluminum is highly chemically reactive, making it a rare metal in its native form. Instead, aluminum is found combined in over 270 different minerals, the most common being bauxite.
In its pure form, aluminum naturally forms a thin outer layer of aluminum oxide when in contact with oxygen through a process called oxidation. This surface layer creates a barrier to further oxidation, as well as corrosion. Aluminum alloys however, provide little protection from corrosion. As a result, aluminum in its alloy form must be passivated by either alclading, chromate conversion coating, or anodizing to prevent corrosion.
Aluminum's unique characteristics make it an extremely versatile material for a wide spectrum of industries. A low density, and high yield strength (200MPa to 600MPa for aluminum alloys) aluminum is an extremely durable metal, while remaining lightweight, ductile, and malleable.