Santabarbaraite is an amorphous ferric hydroxy

phosphate mineral Phosphate minerals contain the tetrahedrally coordinated phosphate (PO43−) anion along sometimes with arsenate (AsO43−) and vanadate (VO43−) substitutions, and chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions that also fit ...

hydrate that was discovered in

Tuscany it, Toscano (man) it, Toscana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Citizenship , demographics1_footnotes = , demographics1_title1 = Italian , demogra ...

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

during 2000.Pratesi G., Cipriani C., Guili G., and Birch W. D. (2003) Santabarbaraite: a new amorphous phosphate mineral. ''European Journal of Mineralogy''.''15'', 185-192 It also can be found in

Victoria, Australia Victoria is a state in southeastern Australia. It is the second-smallest state with a land area of , the second most populated state (after New South Wales) with a population of over 6.5 million, and the most densely populated state in ...

and Lake Baikal,

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive region, geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a ...

.Fagel N., Alleman L. Y., Granina L., Hatert F., Thamo-Bozso E., Cloots R. and Andre L. (2005) Vivianite formation and distribution in Lake Baikal sediments. ''Global and Planetary Change''.''46'', 315-336 This phosphate mineral has a simplified formula Fe₃⁺³(PO₄)₂(OH)₃·5H₂O, which is the same formula of another non-amorphous phosphate mineral called allanpringite. Santabarbaraite occurs as

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...

ic masses after

vivianite Vivianite () is a hydrated iron phosphate mineral found in a number of geological environments. Small amounts of manganese Mn2+, magnesium Mg and calcium Ca may substitute for iron Fe2+ in the structure.Gaines et al (1997) Dana’s New Minera ...

(Fe₂⁺³(PO₄)₂·8H₂O). In the process,

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

vivianite

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

s to form the amorphous santabarbaraite. Pseudomorphism may be seen in Victoria, Australia, in Wannon Falls (originally a well-known locality for vivianite). It also may be seen at Lake Baikal, Siberia where the oxidized santabarbaraite may be seen as a rim surrounding vivianite due to exposure to air.

Physical properties

Due to pseudomorphism, Santabarbaraite samples show elongated and flattened prism habits. The bulk crystal color is brown to light brown, but appears yellow brown when viewed under an optical microscope. The streak color of the mineral is yellow-umber. Santabarbaraite has a vitreous-to-greasy luster and shows no

fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

under ultraviolet light. It is translucent and shows good parting along the cleavage of its original mineral vivianite at . Santabarbaraite's density is 2.24 g/cm³. The mineral is isotropic, with refractive index n=1.659.

Taxonomy

Santabarbaraite is named after Santa Barbara, a mining district in Italy where, in 2000, the mineral was discovered and first described. The district name honors the saint of

miners A miner is a person who extracts ore, coal, chalk, clay, or other minerals from the earth through mining. There are two senses in which the term is used. In its narrowest sense, a miner is someone who works at the rock face; cutting, blasting, ...

Saint Barbara Saint Barbara ( grc, Ἁγία Βαρβάρα; cop, Ϯⲁⲅⲓⲁ Ⲃⲁⲣⲃⲁⲣⲁ; ; ), known in the Eastern Orthodox Church as the Great Martyr Barbara, was an early Christian Lebanese and Greek saint and martyr. Accounts place her in t ...

, which by association, makes santabaraite one of few minerals bearing the name of a woman.

Geologic occurrence

Santabarbaraite occurs in several places. It occurs in the Valderno Superiore lignite-bearing basin in the Santa Barbara mining district, Tuscany, Italy. Santabarbaraite samples may be seen in Victoria, Australia, underlying

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

beneath Wannon Falls. It also is found in samples from Lake Baikal, Siberia.

Biological occurrence

Since its discovery in 2000, this mineral hydrate has been found in the teeth of a living organism, the Gumboot chiton.Persistent polyamorphism in the chiton tooth: From a new biomineral to inks for additive manufacturing
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References

{{Phosphate minerals Phosphate minerals