Brucite

{{Short description|Magnesium hydroxide mineral}} {{Distinguish|Brushite|Brucine}} {{Infobox mineral | name = Brucite | category = Oxide mineral | boxwidth = | boxbgcolor = | image = Brucite-231242.jpg | imagesize = | caption = | formula = Mg(OH)₂ | IMAsymbol=Brc<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = | strunz = 4.FE.05 | system = Trigonal | class = Hexagonal crystal family ({{overline|3}}m)<br>H-M symbol: ({{overline|3}} 2/m) | symmetry = ''P''{{overline|3}}m1 | unit cell = a = 3.142(1)&nbsp;Å, c = 4.766(2)&nbsp;Å; Z&nbsp;=&nbsp;1 | color = White, pale green, blue, gray; honey-yellow to brownish red | habit = Tabular crystals; platy or foliated masses and rosettes – fibrous to massive | twinning = | cleavage = Perfect on {0001} | fracture = Irregular | tenacity = Sectile | mohs = 2.5 to 3 | luster = Vitreous to pearly | refractive = n_ω = 1.56–1.59<br/> n_ε = 1.58–1.60 | opticalprop = Uniaxial (+) | birefringence = 0.02 | pleochroism = | streak = White | gravity = 2.39 to 2.40 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent | other = Pyroelectric | references =<ref name=Mindat>[http://www.mindat.org/min-820.html Brucite] on Mindat.org</ref><ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/brucite.pdf Handbook of Mineralogy]</ref><ref name=Webmin>[http://webmineral.com/data/Brucite.shtml Brucite on Webmineral]</ref> }}

'''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.<ref>{{Greenwood&Earnshaw2nd}}</ref>

==Discovery== Brucite was first described in 1824 by François Sulpice Beudant<ref>{{Cite web|date=2021-01-13|title=Blog {{!}} GeoRarities|url=https://georarities.com/blog/|access-date=2021-06-02|language=en}}</ref> 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.{{cn|date=September 2023}}

==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 ({{chem2|Al(OH)3}}) and mixtures of huntite ({{chem2|Mg3Ca(CO3)4}}) and hydromagnesite ({{chem2|Mg5(CO3)4(OH)2*4H2O}}).<ref>{{cite journal|last=Hollingbery|first=LA|author2=Hull TR|title=The Thermal Decomposition of Huntite and Hydromagnesite - A Review|journal=Thermochimica Acta|year=2010|volume=509|issue=1–2|pages=1–11|url=http://clok.uclan.ac.uk/1139/|doi=10.1016/j.tca.2010.06.012}}</ref><ref>{{cite journal|last=Hollingbery|first=LA|author2=Hull TR|title=The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review|journal=Polymer Degradation and Stability|year=2010|volume=95|issue=12|pages=2213–2225|url=http://clok.uclan.ac.uk/1432|doi=10.1016/j.polymdegradstab.2010.08.019}}</ref> It also constitutes a significant source of magnesium for industry. Although generally deemed safe, brucite can be contaminated with naturally occurring asbestos fibers.<ref>{{cite journal|last1=Malferrari|first1=Daniele|last2=Di Guisseppe|first2=Dario|last3=Scognamiglio|first3=Valentina|last4=Gualtieri|first4=Alessandro F.|title=Commercial brucite, a worldwide used raw material deemed safe, can be contaminated by asbestos|journal=Periodico di Mineralogia|year=2021|volume=90|issue=3|pages=317–324|url=https://rosa.uniroma1.it/rosa04/periodico_di_mineralogia/article/view/17384|doi=10.13133/2239-1002/17384}}</ref>

== Degradation of cement and concrete == When cement or concrete are exposed to {{Chem2|Mg(2+)}} and {{Chem2|SO4(2-)}} ions simultaneously present in seawater, the precipitation of the poorly soluble brucite contributes to enhance the formation of gypsum in the sulfate attack:

{{block indent|style=overflow: scroll|{{Chem2|MgSO4 + Ca(OH)2 + 2 H2O -> Mg(OH)2 + CaSO4 · 2H2O}}}}

The precipitation of insoluble {{Chem2|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 ({{Nowrap|24.63 cm³/mol}}),<ref name="Molar_Volume">{{cite web | title=Data consultation – Minerals – Molar volume | website=BRGM, Thermoddem | url=https://thermoddem.brgm.fr/data/minerals?title=brucite&field_mformulechimique_value= | access-date=2025-07-22}}</ref> 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.<ref name="Lee2002">{{Cite journal| last=Lee| first=Hyomin|author2=Robert D. Cody|author3=Anita M. Cody|author4=Paul G. Spry| year=2002| title=Observations on brucite formation and the role of brucite in Iowa highway concrete deterioration| journal=Environmental and Engineering Geoscience| volume=8| issue=2| pages=137–145| access-date=2009-09-10| doi=10.2113/gseegeosci.8.2.137| bibcode=2002EEGeo...8..137L| url=http://eeg.geoscienceworld.org/cgi/content/abstract/8/2/137| url-access=subscription}}</ref> 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.<ref>{{cite journal |last1=Lee |first1=Hyomin |last2=Cody |first2=Robert D. |last3=Cody |first3=Anita M. |last4=Spry |first4=Paul G. |title=Observations on brucite formation and the role of brucite in Iowa highway concrete deterioration |journal=Environmental and Engineering Geoscience |date=1 May 2002 |volume=8 |issue=2 |pages=137–145 |doi=10.2113/gseegeosci.8.2.137 |bibcode=2002EEGeo...8..137L |url=https://doi.org/10.2113/gseegeosci.8.2.137 |issn=1078-7275|url-access=subscription }}</ref>

{{block indent|style=overflow: scroll|{{Chem2|Ca,Mg(CO3)2 + 2 NaOH → Mg(OH)2 + CaCO3 + Na2CO3}}}}

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

== Gallery == <gallery> Brucite - Killa Saifullah, Pakistan.jpg|Yellow brucite from Balochistan, Pakistan Nemalite.jpg|Nemalite Brucite-169935.jpg|Brucite crystals from the Sverdlovsk Region, Urals, Russia (size: 10.5 x 7.8 x 7.4 cm) Mg(OH)2Xray.jpg|Structure of Mg(OH)₂ </gallery>

==See also== * List of minerals * List of minerals named after people * Portlandite, {{chem2|Ca(OH)2}} * Cookeite, {{chem2|LiAl4(Si3Al)O10(OH)8}}

==References== {{reflist}}

==Further reading== * {{Cite conference|last=Lee |first=Hyomin |author2=Robert D. Cody |author3=Anita M. Cody |author4=Paul G. Spry |year=2000 |title=Effects of various deicing chemicals on pavement concrete deterioration |book-title=Mid-Continent Transportation Symposium 2000 Proceedings |access-date=2009-09-10 |url=http://eco-solutions.net/Effects_of_Various_Deicing_Chemicals.pdf |url-status=dead |archive-url=https://web.archive.org/web/20090320061826/http://eco-solutions.net/Effects_of_Various_Deicing_Chemicals.pdf |archive-date=March 20, 2009 }} * {{Cite journal | last = Lee | first = Hyomin |author2=Robert D. Cody|author3=Anita M. Cody|author4=Paul G. Spry | year = 2002 | title = Observations on brucite formation and the role of brucite in Iowa highway concrete deterioration | journal = Environmental and Engineering Geoscience | volume = 8 | issue = 2 | pages = 137–145 | access-date = 2009-09-10 | doi = 10.2113/gseegeosci.8.2.137 | bibcode = 2002EEGeo...8..137L | url = http://eeg.geoscienceworld.org/cgi/content/abstract/8/2/137 | url-access = subscription }} * {{Cite journal | title = The protective layer and decalcification of C-S-H in the mechanism of chloride corrosion of cement paste | last1 = Wies aw |author2=Kurdowski | journal = Cement and Concrete Research | volume = 34 | issue = 9 | pages = 1555–1559| date = September 2004 | doi = 10.1016/j.cemconres.2004.03.023 | first1 = W }} * {{Cite journal | last = Biricik | first = Hasan |author2=Fevziye Aköz|author3=Fikret Türker|author4=Ilhan Berktay | year = 2000 | title = Resistance to magnesium sulfate and sodium sulfate attack of mortars containing wheat straw ash | journal = Cement and Concrete Research| volume = 30 | issue = 8 | pages = 1189–1197 | doi = 10.1016/S0008-8846(00)00314-8 }}

Category:Magnesium minerals Category:Hydroxide minerals Category:Cement Category:Concrete Category:Trigonal minerals Category:Minerals in space group 164 Category:Luminescent minerals Category:Minerals described in 1824