Aluminium trihydroxide occurs naturally as a component of bauxite. As an amphoteric hydroxide, it dissolves in both acids and bases. Aluminium salts Al³⁺ are formed in acids and aluminates Al(OH)₄- in bases.
Three modifications of the aluminium orthohydroxide Al(OH)3 are known:
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Al(OH)₃-mineral gibbsite (hydrargillite).
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Al(OH)₃-mineral bayerite
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Mineral nordstrandite
Furthermore, there is the aluminium metahydroxide (aluminium oxide hydroxide) AlO(OH), which is poorer in water and of which the following variations exist:
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α-AlO(OH) mineral Diaspor
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γ-AlO(OH) mineral boehmite
On the one hand, the hydroxides provide the basis for calcination to the oxide, on the other hand they are also used in many ways in ceramics, as thermally conductive fillers, as flame retardants and even in special polishing agents.
