Aluminium is everywhere in Earth's crust, yet almost never found as metal
Aluminium ranks third among elements in Earth's crust, behind only oxygen and silicon, but nature almost never leaves it lying around as a bare metal. It clings to oxygen so fiercely that it took until 1825 to announce its discovery, and until 1886 for two engineers to find an affordable way to free it.
Hans Christian Ørsted, the Danish physicist, announced the element in 1825, and the French chemist Henri Sainte-Claire Deville began the first industrial production in 1856. The real turning point came in 1886, when Paul Héroult in France and Charles Martin Hall in the United States independently hit on the same electrolytic method, now called the Hall–Héroult process. Mass production followed, and by 1954 aluminium had overtaken copper as the most produced metal other than iron. Today it is refined from bauxite, a sedimentary rock.
Its appeal comes down to lightness. With a density of 2.70 grams per cubic centimetre, roughly a third that of steel, it is easy to spot by weight alone. The pure metal is soft, with a yield strength of just 7 to 11 megapascals, but alloys reach 200 to 600, which is why aircraft builders rely on it. It is also a fine conductor: an aluminium wire carrying the same current as a copper one weighs about half as much.
That same hunger for oxygen protects it. A thin oxide skin forms the moment the metal meets air, sealing the surface, and anodising thickens this layer deliberately. Polished aluminium reflects visible light about as well as silver, and does even better into the ultraviolet and far infrared, making it a favourite for mirrors. Chilled to 1.2 kelvin, it becomes a superconductor.
Almost all natural aluminium is the single stable isotope 27Al. A radioactive cousin, 26Al, has a half-life of 717,000 years; paired with beryllium-10 it helps date erosion and burial of sediments, and its decay may have melted some early asteroids. Oddly, no living thing is known to use aluminium salts, even though they are abundant and plants and animals tolerate them well.
Source: Aluminium
