Bauxite

Authors: Stefano Caponi, Maria Torres, Kelsie Greenhill

Mineral Name: Bauxite

Chemical Composition: There is no specific mineral composition but it is a mix of aluminum hydroxides and insoluble minerals. The chemical composition of aluminum hydroxide is AI(OH)3.

Color: Bauxite has many color variation, including pink, rustic red, grey, white, cream, and yellow (1).

Streak: Orange

Hardness: a 1 to a 3 but depends on the impurities and the porosity.

Cleavage/Fracture: This mineral does not have cleavage, only fracture (1). This means that, when the mineral breaks, it does so without a pattern and unevenly. Fracture is unlike cleavage, which causes the mineral to break smoothly and in a pattern. This mineral is unevenly rough all around.

Crystal Form: Bauxite has botryoidal crystal forms and in clay like masses. It also has nodules and it contains tiny crystal linings.

Luster: Dull, and earthy

Special Features: Bauxite has a very unique special feature called oolites that is shown in the mineral as many tiny circles wrapped with rings around them (1). The rings form in different colors that causes the background of the mineral to stand out dramatically. Depending on where the mineral is formed, the oolites could be difficult to see.

Varieties: Some minerals associated with bauxite are gibbsite, boehmite and diaspore.

Mineral Group: Hydroxides and oxides because of the different physical properties

Environment: Deposits of bauxite are mainly formed from rocks that contain aluminum. In some locations bauxite may or may not be originally from the site where it is found. It could have possibly been brought in by certain conditions or weather. Gibbsite bauxite are found in the tropics, this hints that the history of this type of bauxite formed in a subtropical type of climate. Boehmite bauxite was found in the environment in southern parts of Europe and in Turkey, and possibly formed in the tropics. (4).

Associated Rock types: Bauxite generally forms from laterite soils that are a result of heavily weathered igneous rocks such as granite, basalt, and syenite. Also, bauxite can form from sedimentary rocks such as limestone, dolostone, and shale. (2)

Occurrence in North America: Found in the southeastern region. (3)

Economic Uses: Bauxite is stripped down in order to obtain the aluminum from within. Refining the mineral creates a white powder. That white powder is aluminum oxide, which has many economic uses because the aluminum can be extracted from this powder. The process in which aluminum is extracted is called electrolysis. Electrolysis is a way to separate the aluminum oxide into ions by the use of sending an electric current through a solution or liquid containing aluminum oxide. In order to get the aluminum oxide to let electricity pass within it it has to either be melted down into a liquid or, through the most inexpensive way, by letting it dissolve in molten cryolite. Obtaining the aluminum helps create products like pop cans, and other materials that can be sold throughout the world (5).

Industrial Uses: Bauxite is used as an oil fuel proppant and it is used during the process of hydraulic fracturing. The rock is fractured through pumping fluid at high pressures into the ground. Once fractured, proppant particles, like bauxite, go into the drill hole keep the fracture open. When the pump stops, the fractures closes trapping the proppant. The particles that weren’t crushed in the reservoir will open, allowing oil and natural gas to flow into the well. Bauxite is also often used to create a sandblasting abrasive of very hard material called calcined alumina, which is a synthetic corundum. Bauxite is crushed into a powder and made into spherical beads through very high temperatures. These beads are then separated by size for different sandblasting equipments and applications.

First Notable Identification: Pierre Berthier found bauxite in les Baux provence, France in 1821. This geologist was the first to note the presence of aluminum in bauxite. (4)

How We Identified It: We identified this mineral by the different color circled rings, oolites, formed throughout it. We also identified it by the fracture, and hardness. The mineral is very earthy, and lightweight.

Don’t Confuse It With: Bauxite is similar to the rock conglomerate; however, the rock conglomerate is hard as it is composed of many other rocks glued together that were able to withstand the constant force of water shaping its constituents. Bauxite is much softer.



Bibliography

  1. “Minerals.net.” Bauxite: The Aluminum Mineral Bauxite Information and Pictures, Minerals.net, www.minerals.net/mineral/bauxite.aspx.

  2. “Bauxite Mining in the United States.” Wikipedia, Wikimedia Foundation, 11 Mar. 2018, en.wikipedia.org/wiki/Bauxite_mining_in_the_United_States.

  3. “Bauxite.” Wikipedia, Wikimedia Foundation, 11 Mar. 2018, en.wikipedia.org/wiki/Bauxite.

  4. “Bauxite Formation.” The Bauxite Index, CBIX, thebauxiteindex.com/en/cbix/industry-101/ bauxite-101/bauxite-formation.

“GCSE Bitesize: Extraction of Aluminium.” BBC, BBC, www.bbc.co.uk/schools/gcsebitesize/ science/add_ocr_pre_2011/chemicals/extractionmetalsrev3.shtml.