Shigaite is a mineral with formula NaAl₃(Mn²⁺)₆(SO₄)₂(OH)₁₈·12H₂O that typically occurs as small, hexagonal crystals or thin coatings. It is named for

Shiga Prefecture is a prefecture of Japan located in the Kansai region of Honshu. Shiga Prefecture has a population of 1,412,916 (1 October 2015) and has a geographic area of . Shiga Prefecture borders Fukui Prefecture to the north, Gifu Prefecture to the north ...

, Japan, where it was discovered in 1985. The formula was significantly revised in 1996, identifying

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

as a previously unknown constituent.

Description

Shigaite occurs as hexagonal tabular crystals up to in size or as thin films and coatings. The mineral can be yellow, burnt orange, brown or black in color. Shigaite occurs in

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

deposits of

manganese ore Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

and is the Mn²⁺ analogue of

motukoreaite Motukoreaite is a mineral with formula Mg6Al3(OH)18 a(H2O)6SO4)2·6H2O (possibly more than one species). The mineral is named for Motukorea, the island in New Zealand where it was discovered. Motukoreaite was first noted in 1941 and officially d ...

.Cooper, p. 91.

Structure

Shigaite consists of

oxycation In chemistry, an oxycation is a polyatomic ion with a positive charge that contains oxygen. Examples * Dioxygenyl ion, * Nitrosonium ion, * Nitronium ion, * Vanadyl ion, VO2+, a very stable oxycation * Uranyl ion, , all natural U6+ occurs in ...

sheets of lMn²⁺₂(OH)₆sup>1+ intercalated with

oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determine ...

sheets of a(H₂O)₆₆(SO₄)₂sup>3−. Linkage between the sheets and within the oxyanion sheet results largely through

hydrogen bonding In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing ...

History

Shigaite was discovered in 1985 in the Ioi Mine, Shiga Prefecture, Japan. The original study, published in the journal ''Neues Jahrbuch für Mineralogie, Monatshefte'', identified the formula as Al₄Mn₇(SO₄)₂(OH)₂₂·8H₂O. The formula was significantly revised in 1996 using a sample from the N'Chwaning Mine, South Africa.Cooper, p. 91. Sodium, discovered to be a component of shigaite, was not identified in the original study. However, an unidentified

volatile Volatility or volatile may refer to: Chemistry * Volatility (chemistry), a measuring tendency of a substance or liquid to vaporize easily * Relative volatility, a measure of vapor pressures of the components in a liquid mixture * Volatiles, a gr ...

had been noted that presumably was a sodium-containing complex.Cooper, p. 96.

Distribution

, shigaite is known from the following sites: *Iron Monarch open cut, South Australia, Australia *Poudrette quarry, Quebec, Canada *Ioi mine, Shiga Prefecture, Japan *Wessels Mine, Northern Cape Province, South Africa *N'Chwaning Mine, Northern Cape Province, South Africa *Homer Mine, Michigan, United States *Bengal Mine, Michigan, United States The

type material In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

is housed in the

National Museum of Natural History The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. In 2021, with ...

in Washington, D.C. as sample 122089.

Association

Shigaite has been found associated with the following minerals: Ioi mine, Japan *

rhodochrosite Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its (rare) pure form, it is typically a rose-red color, but impure specimens can be shades of pink to pale brown. It streaks white, and its Mohs hardness varies bet ...

sonolite Sonolite is a mineral with formula Mn9(SiO4)4(OH,F)2. The mineral was discovered in 1960 in the Sono mine in Kyoto Prefecture, Japan. In 1963, it was identified as a new mineral and named after the Sono mine. Description Sonolite is transparent ...

manganosite Manganosite is a rare mineral composed of manganese(II) oxide MnO. It was first described in 1817 for an occurrence in the Harz Mountains, Saxony-Anhalt, Germany. It has also been reported from Langban and Nordmark, Sweden and at Franklin Furnace ...

* pyrochroite *

jacobsite Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is (Mn,Mg)Fe2O4 or with oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4.

hausmannite Hausmannite is a complex oxide of manganese containing both di- and tri-valent manganese. The formula can be represented as Mn2+Mn3+2O4. It belongs to the spinel group and forms tetragonal crystals. Hausmannite is a brown to black metallic min ...

galaxite Galaxite, also known as 'mangan-spinel' is an isometric mineral belonging to the spinel group of oxides with the ideal chemical formula . Galaxite is the manganese (Mn) rich endmember of the aluminium (Al) series of the spinel group The spinels a ...

Wessels Mine,

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...

leucophoenicite Leucophoenicite is a mineral with formula Mn7(SiO4)3(OH)2. Generally brown to red or pink in color, the mineral gets its name from the Greek language, Greek words meaning "pale purple-red". Leucophoenicite was discovered in New Jersey, US and iden ...

* gageite * caryopilite Iron Monarch,

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

* arsenoclasite *

gatehouseite Gatehouseite is a manganese hydroxy phosphate mineral with formula Mn5(PO4)2(OH)4. First discovered in 1987, it was identified as a new mineral species in 1992 and named for Bryan M. K. C. Gatehouse (born 1932). , it is known from only one mine ...

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of ...

* manganoan ferroan calcite *

barite Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate ( Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and dr ...

Description

Structure

History

Distribution

Association

Notes

References

Bibliography

Further reading