Gibbsite, also known as hydrargillite, is one of the three principal aluminum hydroxide minerals, with the chemical formula Al(OH)₃. It is the most abundant and economically significant of the aluminum hydroxide polymorphs — alongside boehmite and diaspore — and forms a dominant constituent of high-quality bauxite deposits worldwide. Gibbsite crystallizes in the monoclinic system and commonly occurs as platy, tabular, or pseudo-hexagonal crystals that are white to grayish in color, with a pearly to vitreous luster. In the context of bauxite mining, gibbsite content is a critical parameter in determining the processing characteristics and economic value of a bauxite ore body, as gibbsite dissolves more readily in caustic soda solution at lower temperatures (approximately 140°C) compared to boehmite (approximately 200–240°C) and especially diaspore (approximately 260°C), making it the most favorable aluminum mineral for processing through the Bayer process used to produce alumina. Gibbsite forms through the intense chemical weathering (laterization) of aluminosilicate rocks — particularly feldspars, micas, and clay minerals — in tropical and subtropical environments with high rainfall and good drainage, where silica is progressively leached from the weathering profile while aluminum accumulates in the residual laterite as gibbsite. Major gibbsite-dominant bauxite deposits are found in Guinea, Australia, Jamaica, Brazil, and Ghana. Mineralogical analysis using X-ray diffraction (XRD) is the standard method for determining gibbsite content in bauxite samples, alongside quantification of boehmite, diaspore, kaolinite, goethite, hematite, and quartz, all of which influence alumina recovery and refinery efficiency.
