Visit the
Molecular Expressions Website

Photo Gallery
Silicon Zoo
Chip Shots
Screen Savers
Web Resources
Java Microscopy
Win Wallpaper
Mac Wallpaper
Custom Photos
Image Use
Contact Us

Darkfield Digital Image Gallery

Bauxite Ore

As a convenient and common source of alumina, bauxite ore was first commercially mined in Jamaica in 1854. Almost 35 years later, Karl Joseph Bayer described the process (now known as the Bayer Process) that dramatically reduced the cost of aluminum metal production and moved it from the realm of precious metals into that of everyday commodity.

View a low magnification image of a bauxite ore thin section.

The Bayer process, still economically the most feasible method for extracting aluminum from bauxite ore, involves mining, dissolving the alumina at an elevated temperature, adding flocculants, precipitating pure gibbsite, and heating the gibbsite to 1,100 degrees Celsius to yield alumina by calcination. Commonly, bauxite is composed of the aluminum-containing minerals gibbsite (or hydragillite), boehmite, and diaspore; iron-containing minerals hematite, goethite, magnetite, siderite, and ilmenite; titanium-containing minerals anatase, rutile, and brookite; and the silicon-containing minerals halloysite, kaolinite, and quartz. Depending on the proportional mineral content of the bauxite ore, the dissolution and extraction of alumina in the Bayer process is appropriately adjusted. Most of the world's alumina is converted to refined aluminum via the Hall-Héroult process of electrolytic reduction in a molten bath of cryolite.

Bauxites contain hydrated forms of aluminum oxide, which vary in the amount of water of hydration, and are usually claylike and earthy. The material ranges in color from white to deep brown or red, depending on the quantity and diversity of its various components. Characteristic of bauxites is the formation of small, round concretions known as pisolites. The alumina composition of bauxite varies widely between 50 and 70 percent. In France, bauxite was first described from a location named Baux and in the United States, is mined in Alabama, Arkansas, Georgia, and Puerto Rico. Rich bauxite soils contribute to excellent coffee-growing conditions in countries such as Jamaica, Puerto Rico, and Brazil. In spark plug and furnace lining production, bauxite is used as a refractory material. Other uses for bauxite include the creation of alums and alundum.

Bauxite forms most commonly in deeply weathered rocks as a hydrated aluminum oxide ore. In some locations, the parent material is basalt or other volcanic rocks. Australia is the source of approximately 38 percent of the world's supply of bauxite, while Jamaica (11 percent), Papua New Guinea (13 percent), and Brazil (9 percent) follow in production volume. The intended commercial application (abrasive, cement, ceramics, chemical, metallurgical, refractory) serves as a means of classification for the types of bauxite available to refiners. Resulting from the heightened environmental awareness of the 1970s, the worldwide emphasis on recycling, including nonferrous metals such as aluminum, has reduced the value of some bauxite ores by depressing the price of aluminum metal.

Contributing Authors

Cynthia D. Kelly, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.



Questions or comments? Send us an email.
© 1995-2022 by Michael W. Davidson and The Florida State University. All Rights Reserved. No images, graphics, software, scripts, or applets may be reproduced or used in any manner without permission from the copyright holders. Use of this website means you agree to all of the Legal Terms and Conditions set forth by the owners.
This website is maintained by our
Graphics & Web Programming Team
in collaboration with Optical Microscopy at the
National High Magnetic Field Laboratory.
Last Modification Friday, Nov 13, 2015 at 02:19 PM
Access Count Since September 17, 2002: 9509
Visit the website of our partner in introductory microscopy education: