is a silvery
white and ductile member of the boron group of chemical
elements. It has the symbol Al; its atomic number is 13. It
is not soluble in water under normal circumstances.
Aluminium is the most abundant metal in the Earth's crust,
and the third most abundant element therein, after oxygen
and silicon. It makes up about 8% by weight of the Earth’s
solid surface. Aluminium is too reactive chemically to occur
in nature as the free metal. Instead, it is found combined
in over 270 different minerals. The chief source of aluminium is bauxite ore.
Aluminium is remarkable for its ability to resist corrosion
(due to the phenomenon of passivation) and its low density.
Structural components made from aluminium and its alloys are
vital to the aerospace industry and very important in other
areas of transportation and building. Its reactive nature
makes it useful as a catalyst or additive in chemical
mixtures, including being used in ammonium nitrate
explosives to enhance blast power.
Aluminium is a soft, durable, lightweight, malleable metal
with appearance ranging from silvery to dull gray, depending
on the surface roughness. Aluminium is nontoxic,
nonmagnetic, and nonsparking. It is also insoluble in
alcohol, though it can be soluble in water in certain forms.
The yield strength of pure aluminium is 7–11 MPa, while
aluminium alloys have yield strengths ranging from 200 MPa
to 600 MPa. Aluminium has about one-third the density and
stiffness of steel. It is ductile, and easily machined,
cast, and extruded.
Corrosion resistance can be excellent due to a thin surface
layer of aluminium oxide that forms when the metal is
exposed to air, effectively preventing further oxidation.
The strongest aluminium alloys are less corrosion resistant
due to galvanic reactions with alloyed copper. This
corrosion resistance is also often greatly reduced when many
aqueous salts are present however, particularly in the
presence of dissimilar metals.
Aluminium atoms are arranged in a face-centered cubic (FCC)
structure. Aluminium has a high stacking-fault energy of
approximately 200 mJ/m².
Aluminium is one of the few metals that retain full silvery
reflectance in finely powdered form, making it an important
component of silver paints. Aluminium mirror finish has the
highest reflectance of any metal in the 200–400 nm (UV) and
the 3000–10000 nm (far IR) regions, while in the 400–700 nm
visible range it is slightly outdone by tin and silver and
in the 700–3000 (near IR) by silver, gold, and
Aluminium is a good thermal and electrical conductor, by
weight better than copper. Aluminium is capable of being a
superconductor, with a superconducting critical temperature
of 1.2 kelvins and a critical magnetic field of about 100
In the Earth's crust, aluminium is the most abundant (8.13%)
metallic element, and the third most abundant of all
elements (after oxygen and silicon). However, because of its
strong affinity to oxygen, it is almost never found in the
elemental state; instead it is found in oxides or silicates.
Feldspars, the most common group of minerals in the earth's
crust, are aluminosilicates. Native aluminium metal can be
found as a minor phase in low oxygen fugacity environments,
such as the interiors of certain volcanoes.
Although aluminium is an extremely common and widespread
element, the common aluminium minerals are not economic
sources of the metal. Almost all metallic aluminium is
produced from the ore bauxite. Bauxite occurs as a
weathering product of low iron and silica bedrock in
tropical climatic conditions.