Editing Marble (section)

== Chemistry ==

=== Degradation by acids ===
[[Acid]]s react with the calcium carbonate in marble, producing [[carbonic acid]] (which decomposes quickly to CO<sub>2</sub> and H<sub>2</sub>O) and other soluble salts :<ref name="UFIIN">{{Cite web |title=Environmental degradation of marble |url=http://www.whatischemistry.unina.it/en/martmarmo.html |access-date=5 November 2021 |website=What is Chemistry? |publisher=University Federico II of Naples, Italy |archive-date=5 November 2021 |archive-url=https://web.archive.org/web/20211105094636/http://www.whatischemistry.unina.it/en/martmarmo.html |url-status=live }}</ref>
:CaCO<sub>3</sub>(s) + 2H<sup>+</sup>(aq) → Ca<sup>2+</sup>(aq) + CO<sub>2</sub>(g) + H<sub>2</sub>O (l)

Outdoor marble statues, [[headstone|gravestones]], or other marble structures are damaged by [[acid rain]] whether by [[carbonation]], [[sulfation]] or the formation of "black-crust" (accumulation of calcium sulphate, nitrates and carbon particles).<ref name="UFIIN" /> Vinegar and other acidic solutions should be avoided in the cleaning of marble products.

=== Crystallization ===
Crystallization refers to a method of imparting a glossy, more durable finish on to a marble floor (CaCO<sub>3</sub>). It involves polishing the surface with an acidic solution and a steel wool pad on a flooring machine. The chemical reaction below shows a typical process using magnesium fluorosilicate (MgSiF<sub>6</sub>) and [[hydrochloric acid]] (HCl) taking place.

:CaCO<sub>3</sub>(s) +  MgSiF<sub>6</sub>(l) + 2HCl (l) → MgCl<sub>2</sub>(s) + CaSiF<sub>6</sub>(s) + CO<sub>2</sub>(g) + H<sub>2</sub>O(l)

The resulting calcium hexafluorosilicate (CaSiF<sub>6</sub>) is bonded to the surface of the marble. This is harder, more glossy and stain resistant compared to the original surface.

The other often used method of finishing marble is to polish with oxalic acid (H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>), an organic acid. The resulting reaction is as follows:

:CaCO<sub>3</sub>(s) + H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>(l) → CaC<sub>2</sub>O<sub>4</sub>(s) + CO<sub>2</sub>(g) + H<sub>2</sub>O(l)

In this case the calcium oxalate (CaC<sub>2</sub>O<sub>4</sub>) formed in the reaction is washed away with the slurry, leaving a surface that has not been chemically changed.<ref>{{cite web |title=Crystallization vs. Oxalic Acid Polishing |url=https://multimedia.3m.com/mws/media/790119O/crystallization-vs-oxalic-acid-polishing.pdf |publisher=3M |access-date=2021-09-01 |archive-date=2021-09-01 |archive-url=https://web.archive.org/web/20210901231013/https://multimedia.3m.com/mws/media/790119O/crystallization-vs-oxalic-acid-polishing.pdf |url-status=live }}</ref>

=== Microbial degradation ===
The haloalkaliphilic methylotrophic bacterium ''[[Methylophaga murata]]'' was isolated from deteriorating marble in the [[Kremlin]].<ref>{{cite journal |author1=Doronina NV |author2=Li TsD |author3=Ivanova EG |author4=Trotsenko IuA. |date=2005 |title=Methylophaga murata sp. nov.: a haloalkaliphilic aerobic methylotroph from deteriorating marble |journal=Mikrobiologiia |volume=74 |issue=4 |pages=511–9 |pmid=16211855}}</ref> Bacterial and fungal degradation was detected in four samples of marble from [[Milan Cathedral]]; black ''[[Cladosporium]]'' attacked dried [[acrylic resin]]<ref>{{cite journal |author1=Cappitelli F |author2=Principi P |author3=Pedrazzani R |author4=Toniolo L |author5=Sorlini C |year=2007 |title=Bacterial and fungal deterioration of the Milan Cathedral marble treated with protective synthetic resins |journal=Science of the Total Environment |volume=385 |issue=1–3 |pages=172–81 |bibcode=2007ScTEn.385..172C |doi=10.1016/j.scitotenv.2007.06.022 |pmid=17658586}}</ref> using melanin.<ref>{{cite journal |author1=Cappitelli F |author2=Nosanchuk JD |author3=Casadevall A |author4=Toniolo L |author5=Brusetti L |author6=Florio S |author7=Principi P |author8=Borin S |author9=Sorlini C |date=Jan 2007 |title=Synthetic consolidants attacked by melanin-producing fungi: case study of the biodeterioration of Milan (Italy) cathedral marble treated with acrylics |journal=Applied and Environmental Microbiology |volume=73 |issue=1 |pages=271–7 |bibcode=2007ApEnM..73..271C |doi=10.1128/AEM.02220-06 |pmc=1797126 |pmid=17071788}}</ref>