A rusticle is a formation of

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...

similar to an

icicle An icicle is a spike of ice formed when water falling from an object freezes. Formation and dynamics Icicles can form during bright, sunny, but subfreezing weather, when ice or snow melted by sunlight or some other heat source (such as a poor ...

stalactite A stalactite (, ; , ) is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension (chemistry ...

in appearance that occurs deep underwater when iron-loving bacteria attack and

oxidize Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...

and

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

. They may be familiar from underwater photographs of

shipwreck A shipwreck is the wreckage of a ship that is located either beached on land or sunken to the bottom of a body of water. It results from the event of ''shipwrecking'', which may be intentional or unintentional. There were approximately thre ...

s, such as the RMS ''Titanic'' and the German battleship ''Bismarck''. They have also been found in the #3 8-inch gun turret on the stern of the USS ''Indianapolis''. The word ''rusticle'' is a

portmanteau In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together.

of the words ''

'' and ''

'' and was coined by

Robert Ballard Robert Duane Ballard (born June 30, 1942) is an American retired Navy officer and a professor of oceanography at the University of Rhode Island who is noted for his work in underwater archaeology (maritime archaeology and archaeology of ...

, who first observed them on the wreck of the ''Titanic'' in 1986. Rusticles on the ''Titanic'' were first investigated in 1996 by Roy Cullimore, based at the

University of Regina The University of Regina is a public university located in Regina, Saskatchewan, Canada. Founded in 1911 as a private denominational high school of the Methodist Church of Canada, it began an association with the University of Saskatchewan as a j ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. A previously unknown species of

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

living inside the ''Titanic''s rusticles called ''

Halomonas titanicae ''Halomonas titanicae'' is a gram-negative, halophilic species of bacteria which was isolated in 2010 from rusticles recovered from the wreck of the RMS ''Titanic''. It has been estimated by Henrietta Mann, one of the researchers that first iso ...

'' was discovered in 2010 by Henrietta Mann. Rusticles can form on any submerged steel object and have been seen on other subsea structures such as mooring chains and subsea equipment. They form more rapidly in warmer climates and can form in water with little to no

dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can ...

Composition

The rusticle consists of up to 35% iron compounds including

iron oxide An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron ...

iron carbonate Iron(II) carbonate, or ferrous carbonate, is a chemical compound with formula , that occurs naturally as the mineral siderite. At ordinary ambient temperatures, it is a green-brown ionic solid consisting of iron(II) cations and carbonate anions ...

s, and

iron hydroxide An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron oxide ...

s. Rusticles are found in a tube shapes of iron oxides which are vertical to one another. Rusticles are found to grow at approximately 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.Silva-Bedoya, Lina (5 January 2021). "Deep-sea corrosion rusticles from iron-hulled shipwrecks". Wiley.

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 In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

. 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 Iron(III) oxide or ferric oxide is the inorganic compound with the formula . It occurs in nature as the mineral hematite, which serves as the primary source of iron for the steel industry. It is also known as red iron oxide, especially when use ...

, while the core is bright orange due to the presence of crystals of

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

. There are several morphologies of the rusticle, some of which are conical, cylindrical, and rusticle on the seafloor.

References

Corrosion {{Corrosion-stub