Aluminum is the third most abundant element in the earth’s crust after oxygen and silicon and well ahead of iron. It’s in hundreds of common minerals – but it’s almost impossible to get aluminum metal out of most minerals economically. The rock bauxite is the only significant ore of aluminum.
We leave much the work in processing aluminum to nature. There’s a reason most of the world’s reserves of bauxite are in wet, tropical to subtropical nations like Jamaica, Brazil, Guinea, Guyana, India, Indonesia, Viet Nam, southern China, and northern Australia. The climate there leads to intense chemical weathering of rocks, concentrating the aluminum in soils called laterites that solidify into the rock bauxite. Mineralogically, bauxite is mostly aluminum oxides and hydroxides like gibbsite Al(OH)3, boehmite AlO(OH), and diaspore AlO(OH), but they are good starting points toward the production of aluminum metal.
The next steps are complex and expensive enough that until the middle 1880s aluminum metal was more valuable than silver – at times significantly more valuable. An electrolytic process invented in 1886 eventually brought the price down, but today, aluminum processing demands huge amounts of electricity. That’s one of the reasons that Alcoa, the Aluminum Company of America, established a processing plant in Iceland in 2007: Iceland’s electricity is based on cheap hydropower. And that’s also one of the reasons that some bauxite is shipped all the way from Australia to Iceland.
The crazy-quilt graphic at the top is admittedly complex, as it needs to be to suggest how bauxite mined in Australia or Brazil goes to China or Iceland or Canada where it is smelted into aluminum metal for export to the US or Russia or made into finished products in China that are exported to the US and Europe. I realize (and apologize for) the likely difficulty of viewing this graphic on a phone without frustration. It really needs to be 30 or more centimeters wide.
Traces of iron oxides often color bauxite brown, but the common texture you see (as in my specimens here) is rounded bodies called pisolites. Pisolites are essentially small concretions that develop in the soil as various compounds solidify during the weathering process. The name of the soil (and to some extent, the rock that derives from it), laterite, is from a Latin word for brick, reflecting the iron-based brick-red color of much of this material including some bauxite.
One mineral, cryolite (from words meaning “ice stone”), was used for a time as an ore of aluminum, but more as a flux that made processing of bauxite easier. Cryolite is sodium-aluminum fluoride, Na2NaAlF6, and was found in only one place in significant, commercial quantities: Ivigtut (Ivittuut), Greenland. It’s usually white or colorless, and while crystals do form, many specimens (like mine here) are just chunks of rock. Cryolite has the unusual property of seeming to disappear in water, because its refractive index of light is virtually the same as that of water.
Historically some bauxite was produced in Arkansas, where it formed from intense weathering of nepheline syenite (a highly aluminous rock). Today the US produces small quantities of bauxite from Arkansas, Alabama, and Georgia; the USGS withholds the amount to avoid revealing proprietary company information. But while the USGS says US import dependency on bauxite is “greater than 75%,” realistically the US depends on imports for more like 99% of the bauxite it consumes.
Aluminum does exist as a native element, but it is extraordinarily rare compared to other elements like gold, silver, copper, and iron. Aluminum metal was first isolated in 1824 by Danish physicist and chemist Hans Christian Ørsted, but before it was isolated, it was named by British chemist Humphrey Davy, as aluminum in 1808, then as aluminium in 1812. Today the British spelling is the internationally accepted version, but “aluminum” is an accepted variation.
Some of the information in this post is from my 2011 book, What Things Are Made Of, especially pages 93-96. I updated the data to 2022 for the bauxite-aluminum graphic.
None of that American rubbish Richard. It is ALUMIN-I-UM! 🤣