Santabarbaraite is an

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymousl ...

ferric hydroxy

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

hydrate that was discovered in

Tuscany Tuscany ( ; ) is a Regions of Italy, region in central Italy with an area of about and a population of 3,660,834 inhabitants as of 2025. The capital city is Florence. Tuscany is known for its landscapes, history, artistic legacy, and its in ...

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

during 2000. It also can be found in

Victoria, Australia Victoria, commonly abbreviated as Vic, is a state in southeastern Australia. It is the second-smallest state (after Tasmania), with a land area of ; the second-most-populated state (after New South Wales), with a population of over 7 million; ...

and

Lake Baikal Lake Baikal is a rift lake and the deepest lake in the world. It is situated in southern Siberia, Russia between the Federal subjects of Russia, federal subjects of Irkutsk Oblast, Irkutsk Oblasts of Russia, Oblast to the northwest and the Repu ...

Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...

. This phosphate mineral has a simplified formula , 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(II) phosphate mineral found in a number of geological environments. Small amounts of manganese Mn2+, magnesium Mg2+, and calcium Ca2+ may substitute for iron Fe2+ in its structure.Gaines et al (1997) Dana's New ...

(). In the process,

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

vivianite

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 ...

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 one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

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 (mining), face; cutt ...

Saint Barbara Saint Barbara (; ; ; ), known in the Eastern Orthodox Church as the Great Martyr Barbara, was an Early Christianity, early Christian Greek saint and martyr. There is no reference to her in the authentic early Christian writings nor in the origin ...

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

Geologic occurrence

Santabarbaraite occurs in several places. It occurs in the Valderno Superiore

lignite Lignite (derived from Latin ''lignum'' meaning 'wood'), often referred to as brown coal, is a soft, brown, combustible sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35% and is considered the lowest ...

-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 (geology), epoch in the geologic time scale that extends from 5.33 to 2.58basalt Basalt (; ) is an aphanite, 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 planetary surface, surface of a terrestrial ...

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 The gumboot chiton (''Cryptochiton stelleri''), also known as the giant western fiery chiton or giant Pacific chiton, is the largest of the chitons, growing to and capable of reaching a weight of more than . It is found along the shores of the n ...

References

{{Phosphate minerals Phosphate minerals