Gibbsite

Gibbsite is an important ore of aluminium in that it is one of three main phases that make up the rock bauxite.

Gibbsite has three named structural polymorphs or polytypes: bayerite (designated often as α-Al(OH)3,[2]: 2  but sometimes as β-Al(OH)3)[citation needed], doyleite, and nordstrandite.

The sheets are only held together by weak residual bonds and this results in a very soft easily cleaved mineral.

However the lower charge in brucite's magnesium (+2) as opposed to gibbsite's aluminium (+3) does not require that one third of the octahedrons be vacant of a central ion in order to maintain a neutral sheet.

[5] The lattice parameters for gibbsite depending upon the particular method used to measure or calculate them and are therefore displayed as ranges below.

Ball-and-stick model of the part of the crystal structure of gibbsite