Brucite

Key takeaways

Brucite 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 Brucite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Brucite from memory before moving on to harder problems.

Reference excerpt

Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc and chrysotile. It adopts a layered CdI2-like structure with hydrogen-bonds between the layers.

Discovery Brucite was first described in 1824 by François Sulpice Beudant and named for the discoverer, American mineralogist, Archibald Bruce (1777–1818). A fibrous variety of brucite is called nemalite. It occurs in fibers or laths, usually elongated along [1010], but sometimes [1120] crystalline directions.

Occurrence A notable location in the US is Wood's Chrome Mine, Cedar Hill Quarry, Lancaster County, Pennsylvania. Yellow, white and blue brucite with a botryoidal habit was discovered in Qila Saifullah District of Province Baluchistan, Pakistan. In a later discovery, brucite also occurred in the Bela Ophiolite of Wadh, Khuzdar District, Province Baluchistan, Pakistan. Brucite has also occurred from South Africa, Italy, Russia, Canada, and other localities as well, but the most notable discoveries are the US, Russian and Pakistani examples.

Industrial applications Synthetic brucite is mainly consumed as a precursor to magnesia (MgO), a useful refractory and thermal insulator. It finds some use as a flame retardant because it thermally decomposes to release water in a similar way to aluminium hydroxide (Al(OH)3) and mixtures of huntite (Mg3Ca(CO3)4) and hydromagnesite (Mg5(CO3)4(OH)2·4H2O). It also constitutes a significant source of magnesium for industry. Although generally deemed safe, brucite can be contaminated with naturally occurring asbestos fibers.

Degradation of cement and concrete When cement or concrete are exposed to Mg2+ and SO2−4 ions simultaneously present in seawater, the precipitation of the poorly soluble brucite contributes to enhance the formation of gypsum in the sulfate attack:

The precipitation of insoluble Mg(OH)2 helps to considerably drive the chemical equilibrium of the reaction to the right. It exacerbates the sulfate attack resulting in the formation of gypsum and ettringite (an expansive phase) responsible for the mechanical stress in the hardened cement paste. However, brucite, a phase with a small molar volume (24.63 cm3/mol), may contribute to clogging the porous network in the hardened cement paste, hindering the diffusion of these harmful reactive species in the cement matrix. This can delay the decalcification of the C-S-H phase (the "glue" phase in the hardened cement paste responsible for the cohesion in concrete) and its transformation into an M-S-H phase. The exact mechanism of brucite degradation of hardened cement paste remains a matter of debate. If brucite had a high molar volume, it could be de facto considered a swelling phase (like ettringite, or highly hydrated minerals), but this does not appear to be the case. It is unclear if it causes expansion or not, and how. If it replaces another phase locally (topo chemical replacement), in cases where its molar volume is smaller than that of the phase it replaces, no expansion is expected; rather, a decrease in porosity is anticipated. However, if it crystallizes in a large number of tiny crystals growing between existing ones, even with a small molar volume, it could exert a considerable crystallization pressure in the cement matrix, resulting in tensile stress, expansion and cracking. Anyway, prolonged contact between seawater, or naturally rich Mg-brines, and concrete may induce durability issues for regularly immersed concrete structures, and their components, especially if they also contain steel reinforcements (pitting corrosion caused by chloride ions). The use of dolomite as aggregate in concrete made with a cement with a too high alkali content can also cause brucite precipitation, driving the dedolomitization reaction, as observed in the alkali-aggregate reaction.

Consequently, the use of dolomite is prohibited as aggregate for concrete.

Gallery

See also List of minerals List of minerals named after people Portlandite, Ca(OH)2 Cookeite, LiAl4(Si3Al)O10(OH)8

References

Further reading Lee, Hyomin; Robert D. Cody; Anita M. Cody; Paul G. Spry (2000). "Effects of various deicing chemicals on pavement concrete deterioration" (PDF). Mid-Continent Transportation Symposium 2000 Proceedings. Archived from the original (PDF) on March 20, 2009. Retrieved 2009-09-10. Lee, Hyomin; Robert D. Cody; Anita M. Cody; Paul G. Spry (2002). "Observations on brucite formation and the role of brucite in Iowa highway concrete deterioration". Environmental and Engineering Geoscience. 8 (2): 137–145. Bibcode:2002EEGeo...8..137L. doi:10.2113/gseegeosci.8.2.137. Retrieved 2009-09-10. Wies aw, W; Kurdowski (September 2004). "The protective layer and decalcification of C-S-H in the mechanism of chloride corrosion of cement paste". Cement and Concrete Research. 34 (9): 1555–1559. doi:10.1016/j.cemconres.2004.03.023. Biricik, Hasan; Fevziye Aköz; Fikret Türker; Ilhan Berktay (2000). "Resistance to magnesium sulfate and sodium sulfate attack of mortars containing wheat straw ash". Cement and Concrete Research. 30 (8): 1189–1197. doi:10.1016/S0008-8846(00)00314-8.

Illustrations

Worked examples

Example 1 — a first encounter with Brucite

Start with the simplest possible case. Write down what Brucite 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 Brucite 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 Brucite 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 Brucite

In research: Brucite 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 Brucite 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: Brucite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cement, Concrete, Hydroxide minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Brucite 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.

How to study Brucite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Brucite 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 Brucite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Brucite in simple terms?

Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites.

Why does Brucite 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 Brucite?

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 Brucite.