Bobfergusonite is a mineral with formula Na₂Mn₅FeAl(PO₄)₆. The mineral varies in color from green-brown to red-brown. It was discovered in 1986 in Manitoba, Canada, and named for Robert Bury Ferguson (born 1920). , the mineral has only been found in Canada and Argentina.

Description

Bobfergusonite occurs as equant anhedral single crystals up to in size or as nodular aggregates of few crystals.Ercit, p. 600. The mineral varies in color from green-brown to red-brown. Thin fragments of bobfergusonite are transparent. Bobfergusonite has been found in association with

alluaudite Alluaudite is a relatively common alkaline manganese iron phosphate mineral with the chemical formula . It occurs as metasomatic replacement in granitic pegmatites and within phosphatic nodules in shales. It was first described in 1848 for an oc ...

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

, beusite, fillowite, and

triplite Triplite is a rare phosphate mineral with formula: . It occurs in phosphate-rich granitic pegmatites typically as irregular brown opaque masses. Triplite was first described in 1813 for an occurrence in Chanteloube, Limousin, France.pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

Structure

Bobfergusonite has a layered crystal structure topologically identical to that of alluaudite and wyllieite but with differences in the ordering of metal

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s. The two types of layer alternate along ''Y''. One layer consists of chains of metal cation octahedra cross-linked by phosphate tetrahedra. Within the chains metal cations are ordered M³⁺–M²⁺ in a similar fashion to wyllieite. However, the structure of bobfergusonite is distinct by the presence of Al and Fe³⁺ ordering between chains. The other layer, identical to its wyllieite counterpart, consists of chains running parallel to ''X'': one consisting of alternating, face-sharing sodium and manganese polyhedra and the other edge-sharing sodium polyhedra. These chains are not cross-linked but bind the other layers together.Ercit, p. 605.

History

Alan J. Anderson discovered large brown crystals in a granitic

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

at Cross Lake in Manitoba. Study by electron microprobe and

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

identified it as a new mineral related to the wyllieite and alluaudite groups. The mineral was named for professor Robert Bury Ferguson to celebrate his 65th birthday and retirement from the University of Manitoba.Ercit, p. 599. The mineral and the name bobfergusonite were approved by the IMA Commission on New Minerals and Mineral Names.

Distribution

, bobfergusonite is known from the Nancy

in Argentina and the Gottcha Claim in Manitoba, Canada. 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 the ...

is held at the University of Manitoba and the

Royal Ontario Museum The Royal Ontario Museum (ROM) is a museum of art, world culture and natural history in Toronto, Ontario, Canada. It is one of the largest museums in North America and the largest in Canada. It attracts more than one million visitors every year ...

in Toronto.

References

Bibliography

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External links

Images of bobfergusonite
from mindat.org Monoclinic minerals Minerals in space group 14 Sodium minerals Manganese(II) minerals Iron(III) minerals Aluminium minerals Phosphate minerals