The sheets are only held together by weak residual bonds and this results in a very soft easily cleaved mineral. The different symmetry of gibbsite and brucite is due to the different way that the layers are stacked. The basic structure of corundum is identical to gibbsite except the hydroxides are replaced by oxygen. Since oxygen has a charge of -2 the layers are not neutral and require that they must be bonded to other aluminums above and below the initial layer producing the framework structure that is the structure of corundum. Gibbsite is interesting for another reason because it is often found as a part of the structure of other minerals.
Color is white or colorless with shades of gray, blue and green.
Transparency Crystals are translucent and rarely transparent. Crystal Habit is usually massive but rare crystals are found in flattened tabular crystals. In many bauxite specimens gibbsite is found in a pisolitic habit. Also found as botryoidal encrustations, concretionary, stalactitic and foliated masses. Cleavage is perfect in one direction, basal.