Gatehouseite is a

manganese 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 ...

hydroxy

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

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 in

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 ...

Description

Gatehouseite occurs as radiating or divergent groups of bladelike crystals up to 100 μm by 20 μm by 5 μm in size and as overgrowths on arsenoclasite that are up to 5 mm long. The transparent mineral can be brownish-orange or yellow in color. Gatehouseite is the

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

analogue of arsenoclasite. The mineral occurs in cavities in sedimentary iron and manganese deposits in association with arsenoclasite,

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

, hematite,

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 minera ...

triploidite Triploidite is an uncommon manganese iron phosphate mineral with formula: . It crystallizes in the monoclinic crystal system and typically occurs as elongated and striated slender prisms which may be columnar to fibrous. Its crystals may be pink ...

, barite, and manganoan ferroan calcite. Based on a 1977 experiment that produced triploidite, it is likely that gatehouseite formed by a reaction between hausmannite and basic phosphorus-rich fluids at low temperature and variable pH conditions.

History

In May 1987, Glyn Francis, an employee at the Iron Monarch mine in South Australia, submitted for identification some mineral specimens from the mine to A. Pring. Very small, unidentified pale brownish orange crystals were seen in one specimen; study showed they had a formula of the type ''M''₅(''X''O₄)₂(OH)₄ and contained

, and a minor quantity of

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...

. The powder X-ray diffraction pattern could not be recorded as insufficient material was available. Another specimen in the same group consisted of arsenoclasite crystals overgrown by what appeared to be its as yet undescribed phosphorus analogue. Francis later discovered more of the brownish orange crystals in sufficient quantity to obtain an X-ray

diffraction pattern Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a ...

. This proved that the crystals and the overgrowths were the same, new mineral species. Gathehouseite was named for Bryan Michael Kenneth Cummings Gatehouse for his contributions to the study of oxides and oxysalts. The Commission on New Minerals and Mineral Names recognized the mineral and approved its name in 1992 (IMA 1992-016). Due to the small size and intergrowth of the crystals, single-crystal X-ray crystallography is difficult to perform on gatehouseite. In 2011, this technique was successfully used to determine the crystal structure of the mineral.

Distribution

The type material is housed at the

South Australian Museum The South Australian Museum is a natural history museum and research institution in Adelaide, South Australia, founded in 1856 and owned by the Government of South Australia. It occupies a complex of buildings on North Terrace in the cultu ...

in Adelaide and the

Museum of Victoria Museums Victoria is an organisation which operates three major state-owned museums in Melbourne, Victoria: the Melbourne Museum, the Immigration Museum and Scienceworks Museum. It also manages the Royal Exhibition Building and a storage faci ...

in Melbourne. , the Iron Monarch open cut remains the only site from which gatehouseite is known.

Crystal structure

Gatehouseite has the

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...

P2₁2₁2₁. The crystal structure consists of Mn(O, OH)₆

octahedra In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...

and PO₄

tetrahedra In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...

. The five manganese sites are occupied by manganese and small amounts of magnesium. The two phosphorus sites are occupied by phosphorus and small amounts of silicon and arsenic.

References

Bibliography

* *{{cite journal, last1=Pring, first1=A., last2=Birch, first2=W.D., year=1993, title=Gatehouseite, a New Manganese Hydroxy Phosphate from Iron Monarch, South Australia, journal=Mineralogical Magazine, volume=57, issue= 387, pages=309–313, publisher=The Mineralogical Society, doi=10.1180/minmag.1993.057.387.13, bibcode=1993MinM...57..309P, s2cid=140568230 , url=http://www.minersoc.org/pages/Archive-MM/Volume_57/57-387-309.pdf, access-date=May 22, 2012

External links

Images of gatehouseite
from mindat.org Phosphate minerals Orthorhombic minerals Minerals in space group 19