Bauxite
Image: Darla Sondrol (CC0)
Mineral NameBauxite
Chemical FormulaMixture of aluminum hydroxides and oxides, primarily gibbsite (Al(OH)3), boehmite (AlO(OH)), and diaspore (AlO(OH))
Mohs Hardness1
Crystal Systemamorphous
Lusterearthy
Streak Colorwhite to reddish-brown
Cleavagenone
Fractureuneven
Specific Gravity2
Colorsreddish-brown, brown, white, gray, yellow
Transparencyopaque
Mineral GroupRock (sedimentary), composed of aluminum hydroxides/oxides
Usesaluminum production, abrasives, refractories
Associated Mineralsgibbsite, diaspore, boehmite, kaolinite, hematite, goethite
Raritycommon
Description
This sample of bauxite is about 12 cm across, displaying a reddish-brown color and a distinct pisolitic (pea-sized spherical aggregates) texture. It is an earthy, dull-looking rock, characteristic of its mixed mineral composition.
Geological Context
Bauxite forms as a residual deposit from intense chemical weathering of aluminum-rich rocks (e.g., granites, basalts, shales) in tropical and subtropical climates, where silica is leached away, concentrating aluminum hydroxides.
