earth science

Gibbsite

Gibbsite is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Gibbsite rather than just read about it. In short: Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3).

Key takeaways

Gibbsite belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Gibbsite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gibbsite from memory before moving on to harder problems.

Reference excerpt

Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3). It is also sometimes called hydrargillite (or hydrargyllite). 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, 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.

Structure 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.

Mineralogical properties

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

References

Further reading Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7

Illustrations

Worked examples

Example 1 — a first encounter with Gibbsite

Start with the simplest possible case. Write down what Gibbsite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Gibbsite before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Gibbsite ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Gibbsite

In research: Gibbsite appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Gibbsite in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Gibbsite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminium minerals, Hydroxide minerals, Luminescent minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Gibbsite outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Gibbsite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gibbsite means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Gibbsite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gibbsite in simple terms?

Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3).

Why does Gibbsite matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Gibbsite?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Gibbsite.