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 ...

stalactite A stalactite (, ; from the Greek 'stalaktos' ('dripping') via ''stalassein'' ('to drip') 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 an ...

in appearance that occurs deep underwater when wrought iron oxidizes. 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. Shipwrecking may be intentional or unintentional. Angela Croome reported in January 1999 that there were approximately ...

s, such as the RMS ''Titanic'' and the German battleship ''Bismarck''. They have also been found in the #3 turret, 8-inch gun turret on the stern remains in place of the USS ''Indianapolis''. Rusticles are created by microbial organisms that consume iron. The word ''rusticle'' is a

portmanteau A portmanteau word, or portmanteau (, ) is a blend of wordsrust 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) ...

'' 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 most noted for his work in underwater archaeology: maritime archaeology and archaeology ...

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

University of Regina The University of Regina is a public research 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 Saskatche ...

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, covering over , making it the world ...

. A previously unknown species of bacteria living inside the ''Titanic''s rusticles called '' Halomonas titanicae'' 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 ca ...

Composition

The rusticle consists of up to 35% iron compounds including iron oxides, iron carbonates and iron hydroxides. 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 sulphate 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 to allow water to flow through, and they seem to be built 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, including only woody plants with secondary growth, plants that ar ...

. They are very delicate and can easily disintegrate into fine powder on even the slightest touch.

Colors

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 Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally ...

, 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 rusticles on the seafloor.

References

Corrosion {{corrosion-stub