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 landlocked prefecture of Japan in the Kansai region of Honshu. Shiga Prefecture has a population of 1,398,972 as of 1 February 2025 and has a geographic area of . Shiga Prefecture borders Fukui Prefecture to the north, Gifu Prefecture to th ...

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

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

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; it has symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition metal with a multifac ...

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 de ...

.Cooper, p. 91.

Structure

Shigaite consists of

oxycation In chemistry, an oxycation is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). They usually end with the suffix "-ium" or "-yl". However, the International Union of Pure and Applied Chemist ...

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 (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

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 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 wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

is housed in the

National Museum of Natural History The National Museum of Natural History (NMNH) 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. With 4.4 ...

in Washington, D.C. as sample 122089.

Association

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

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

rhodochrosite Rhodochrosite is a manganese carbonate mineral with chemical composition Manganese(II) carbonate, MnCO3. In its pure form (rare), it is typically a rose-red colour, but it can also be shades of pink to pale brown. It Streak (mineralogy), streak ...

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 t ...

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 Furn ...

* 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 Redox, oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4.

hausmannite Hausmannite is a complex oxide, or a mixed oxide, of manganese containing both Divalent, di- and Trivalent, tri-valent manganese. Its chemical formula can be represented as , or more simply noted as , or , as commonly done for magnetite (), the co ...

galaxite Galaxite, also known as 'mangan-spinel' is an Cubic crystal system, isometric mineral belonging to the spinel group of oxide minerals, oxides with the ideal chemical formula . It is sometimes used as a gemstone.Tables of Gemstone Identification By ...

Wessels Mine,

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

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 words meaning "pale purple-red". Leucophoenicite was discovered in New Jersey, US and identified as a new ...

* gageite *

caryopilite Caryopilite (synonymous with ectropite and ektropite) is a brown-colored mineral with formula (Mn2+,Mg)3Si2O5(OH)4. The mineral was discovered in 1889 from a mine in Sweden. It was named for the Greek words for walnut and felt in reference to its ...

Iron Monarch,

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

arsenoclasite Arsenoclasite (originally arsenoklasite) is a red or dark orange brown mineral with formula Mn5(AsO4)2(OH)4. The name comes from the Greek language, Greek words ''αρσενικόν'' (for arsenic) and ''κλάσις'' (for cleavage (crystal), cle ...

* gatehouseite *

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 Hydrate, 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, drywall and blackboard or sidewalk ...

Description

Structure

History

Distribution

Association

Notes

References

Bibliography

Further reading