How do I identify Gibbsite?

Gibbsite can be identified by its hardness of 2.5 - 3 on the Mohs scale, White color, Pearly, Vitreous, Dull, Sub-vitreous luster, Monoclinic crystal system. Look for these key characteristics when examining specimens.

What color is Gibbsite?

Gibbsite typically appears in White, light gray, light green, reddish white, reddish yellow impure. Color can vary depending on impurities and formation conditions.

How hard is Gibbsite?

Gibbsite has a hardness of 2.5 - 3 on the Mohs scale. This makes it a soft mineral that can be scratched easily.

Gibbsite

A variety of Minerals

Rare

What is Gibbsite?

Since gibbsite is predominately made of aluminum, it is widely used in metal alloy production. It is found within another mineral, Bauxite, and acts as a binding agent for other minerals. It is named after George Gibbs, a world-renowned mineral collector from the US that lived during the 18th century.

Etymology & Origins

Gibbsite is named after George Gibbs (1776–1833), an American mineral collector.

Uses & Applications

Gibbsite is an important source of aluminum, which is an essential metal used in many objects such as foil, window frames, utensils, and cans. Because the crystals it forms are unremarkable and usually tiny, it is not considered for jewelry nor interesting to collectors.

Gibbsite Market Value Calculator

Estimate the market value of Gibbsite using size, quality, and finish. This preview calculator is for quick context and is not a formal appraisal.

Gibbsite Localities Map

See where Gibbsite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.

Map preview

North ZoneCentral RidgeSouth Basin

Key Characteristics

Rock Types of Gibbsite

Gibbsite has three named structural polymorphs or polytypes: bayerite (designated often as α-Al(OH)3, but sometimes as β-Al(OH)3), doyleite, and nordstrandite. Gibbsite can be monoclinic or triclinic, while bayerite is monoclinic. Doyleite and nordstrandite are triclinic forms.

Composition of Gibbsite

The structure of gibbsite is interesting and analogous to the basic structure of the micas. The basic structure forms stacked sheets of linked octahedra. Each octahedron is composed of an aluminium ion bonded to six hydroxide groups, and each hydroxide group is shared by two aluminium octahedra. One third of the potential octahedral spaces are missing a central aluminium. The result is a neutral sheet: with aluminium as a +3 ion and hydroxide a –1 ion, the net cationic charge of one aluminium per six hydroxides is (+3)/6 = +1/2, and likewise the net anionic charge of one hydroxide per two aluminium atoms is (-1)/2 = -1/2. The lack of a charge on the gibbsite sheets means that there is no charge to retain ions between the sheets and act as a "glue" to keep the sheets together. The sheets are only held together by weak residual bonds and this results in a very soft easily cleaved mineral. Gibbsite's structure is closely related to the structure of brucite, Mg(OH)2. 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. The different symmetry of gibbsite and brucite is due to the different way that the layers are stacked. It is the gibbsite layer that in a way forms the "floor plan" for the mineral corundum, Al2O3. 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 aluminiums 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. The neutral aluminium hydroxide sheets are found sandwiched between silicate sheets in important clay groups: the illite, kaolinite, and montmorillonite/smectite groups. The individual aluminium hydroxide layers are identical to the individual layers of gibbsite and are referred to as the gibbsite layers. The lattice parameters for gibbsite depending upon the particular method used to measure or calculate them and are therefore displayed as ranges below. An Al-Al interlayer spacing of 0.484 or 0.494 nm has been reported.