View source for Rusticle

{{Short description|Rust formation often on shipwrecks}}
[[File:Detached rusticles hires.jpg|right|thumb|Detached rusticles below port side anchor of the [[Titanic|RMS ''Titanic'']]]]
A '''rusticle''' is a formation of [[rust]] similar to an [[icicle]] or [[stalactite]] in appearance that occurs deep underwater when iron-eating bacteria attack and [[redox|oxidize]] [[wrought iron]] and [[steel]]. They may be familiar from underwater photographs of [[shipwreck]]s, such as the [[wreck of the Titanic|RMS ''Titanic'']] and the [[German battleship Bismarck#Wreckage|German battleship ''Bismarck'']]. They have also been found in the #3 8-inch gun turret on the stern of the [[USS Indianapolis (CA-35)|USS ''Indianapolis'']].<ref>{{cite web |title=USS Indianapolis: The Final Chapter |url=https://www.pbs.org/show/uss-indianapolis/ |access-date=February 16, 2024}}</ref> 
The word ''rusticle'' is a [[blend word|portmanteau]] of the words ''[[rust]]'' and ''[[icicle]]'' and was coined by [[Robert Ballard]], who first observed them on the wreck of the [[RMS Titanic|''Titanic'']] in 1986.<ref name=Bacteria>{{cite news |title=New species of bacteria found in Titanic 'rusticles' |newspaper=BBC News |date=6 December 2010 |accessdate=1 March 2012 |url=https://www.bbc.co.uk/news/science-environment-11926932}}</ref> Rusticles on the ''Titanic'' were first investigated in 1996 by Roy Cullimore, based at the [[University of Regina]] in [[Canada]]. A previously unknown species of [[bacteria]] living inside the ''Titanic''{{'}}s rusticles called ''[[Halomonas titanicae]]'' was discovered in 2010 by Henrietta Mann.<ref name="Henrietta Mann">{{cite web |title=Titanic being dissolved by newly ID'd bacteria |publisher=CBC News |date=December 6, 2010 |url=https://www.cbc.ca/news/science/titanic-being-dissolved-by-newly-id-d-bacteria-1.882011 |access-date=April 21, 2022}}</ref>

Rusticles can form on any submerged steel object and have been seen on other subsea structures such as mooring chains<ref name=chain/> and subsea equipment. They form more rapidly in warmer climates and can form in water with little to no [[oxygen saturation|dissolved oxygen]].<ref name="chain">{{cite web |title=Microbiologically influenced corrosion of Gulf of Mexico mooring chain at 6,000 feet depths |url=http://www.intermoor.com/information-center-23/technical-articles-26/omae-2012-84067-microbiologically-influenced-corrosion-of-gulf-of-mexico-mooring-chain-at-6-000-feet-depths-317 |access-date=2013-02-14 |url-status=dead |archive-url=https://web.archive.org/web/20161006100634/http://www.intermoor.com/information-center-23/technical-articles-26/omae-2012-84067-microbiologically-influenced-corrosion-of-gulf-of-mexico-mooring-chain-at-6-000-feet-depths-317 |archive-date=2016-10-06}}</ref>

==Composition==
The rusticle consists of up to 35% iron compounds including [[iron oxide]]s, [[iron carbonate]]s, and [[iron hydroxide]]s. Rusticles are found in a tube shapes of iron oxides which are vertical to one another. Rusticles are found to grow at approximately {{cvt|1|cm}} a year and are most often found in areas of sunken hulls underwater.

The remainder of the structure is a complex community of symbiotic or mutualistic microbes including bacteria ''Halomonas titanicae'' and fungi that use the rusting metal as a source of food, causing microbial corrosion and collectively producing the mineral compounds that form the rusticle as waste products.

Rusticles have been found to most often be composed of iron, calcium, chloride, magnesium, silica, sodium, and sulfate while there are other chemical compositions of rusticles but in much smaller quantities.<ref>Silva-Bedoya, Lina (5 January 2021). "Deep-sea corrosion rusticles from iron-hulled shipwrecks". Wiley.</ref>

==Structure==
Structurally, rusticles contain channels which allow water to flow through, and they seem to build up in a ring structure similar to the growth rings of a [[tree]]. They are very delicate and can easily disintegrate into fine powder on even the slightest touch.

==Colours==
The outer surface of a rusticle is smooth red in appearance from the [[iron(III) oxide]], while the core is bright orange due to the presence of crystals of [[goethite]]. There are several morphologies of the rusticle, some of which are conical, cylindrical, and rusticle on the seafloor.

==References==
{{Reflist}}

[[Category:Corrosion]]


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