Bonaccordite is a rare mineral discovered in 1974. Its chemical formula is Ni₂FeBO₅ and it is a mineral of the

ludwigite Ludwigite is a magnesium-iron borate mineral: Mg2FeBO5. Ludwigite typically occurs in magnesian iron skarn and other high temperature contact metamorphic deposits. It occurs in association with magnetite, forsterite, clinohumite and the borates ...

group. It usually crystallizes in long, cylindrical prisms that form within another source. It is named after the area of Bon Accord, where it was first found. There have also been findings of bonaccordite within nuclear plants at multiple companies. It builds up a deposit within the machines and is a very hard mineral to clean out because it is resistant to ordinary techniques.

History

Bonaccordite was first described in 1974 for an occurrence in the Bon Accord area, Barberton,

Transvaal Transvaal is a historical geographic term associated with land north of (''i.e.'', beyond) the Vaal River in South Africa. A number of states and administrative divisions have carried the name ''Transvaal''. * South African Republic (1856–1902; ...

, South Africa.Webmineral data
/ref> It occurs in a tabular nickeliferous

serpentinite Serpentinite is a metamorphic rock composed predominantly of serpentine group minerals formed by serpentinization of mafic or ultramafic rocks. The ancient origin of the name is uncertain; it may be from the similarity of its texture or color ...

, on the margin of an

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are usua ...

intrusive. The actual site of the bonaccordite finding is a possible

meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...

site three kilometers west of the Scotia talc mine.Handbook of Mineralogy
/ref>

Composition

The chemical formula for bonaccordite is Ni₂FeBO₅. The two analysts confirmed the presence of boron by using wet-chemical analysis.

Geologic occurrence

Bonaccordite can occur as either a cluster of thin, long prisms or rosette-like radiating groups. The prisms can form veins through other minerals and the radiating groups can occur in minerals like liebenbergite or

trevorite Trevorite is a rare nickel iron oxide mineral belonging to the spinel group. It has the chemical formula NiFe3+2O4. It is a black mineral with the typical spinel properties of crystallising in the cubic system, black streaked, infusible and insol ...

.De Waal S.A., Viljoen E.A., Calk L.C. (1974) Nickel Minerals form Barberton, South Africa: VII Bonaccordite. The Nickel Analogue of Ludwigite. Transactions of the Geological Society of South Africa. 77, p 375 Bonaccordite usually occurs along with trevorite, liebenbergite, népouite,

nimite The chlorites are the group of phyllosilicate minerals common in low-grade metamorphic rocks and in altered igneous rocks. Greenschist, formed by metamorphism of basalt or other low-silica volcanic rock, typically contains significant amounts o ...

, gaspeitev, and

millerite Millerite or ''nickel blende'' is a nickel sulfide mineral, Ni S. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates. It can be distinguished from pentlandite by crystal habit, its duller ...

in the area of Bon Accord.Fleischer M., Cabri L. (1976) New Mineral Names. American Mineralogist. 61, P 502-504. All of these minerals crystallize as slender prisms.

Physical properties

Bonaccordite is an opaque mineral with a reddish-brown color. In reflected light, the color is grey with a brownish tinge with strong, reddish-brown internal reflections. In many cases, bonaccordite crystallizes into long, slender cylinders. It has been discovered to be the nickel analogue of

. The

Mohs hardness The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fair ...

for bonaccordite is 7 and its density is 5.17 g/cm³. The optical class is

biaxial In crystal optics, the index ellipsoid (also known as the optical indicatrix or sometimes as the dielectric ellipsoid) is a geometric construction which concisely represents the refractive indices and associated polarizations ...

. Bonaccordite has an

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

crystal system with a

point group In geometry, a point group is a group (mathematics), mathematical group of symmetry operations (isometry, isometries in a Euclidean space) that have a Fixed point (mathematics), fixed point in common. The Origin (mathematics), coordinate origin o ...

of 2/m 2/m 2/m. The crystals are structured as elongated prisms within another material. There has been no observed cleavages or twinning. Space group has been determined as 'Pbam''and cell dimensions were calculated to a = 9.213(6) b = 12.229(7) c = 3.001(2) Z = 4. Bonaccordite is

insoluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

and has only shown reactivity to

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

. It is very hard to clean it off of fuel rods in nuclear power reactors where it is sometimes formed.Deshon J. (2003) Advisory Committee on Reactor Safeguards Reactor Fuels Subcommittee - Open Session. United States of America Nuclear Regulatory Committee.Sawicki J.A. (2008) Evidence of Ni₂FeBO₅ and m-ZrO₂ precipitates in fuel rod deposits in AOA-affected high boiling duty PWR core. Journal of Nuclear Materials. 374, p 248-269. It has been shown to form hydrothermally in near-supercritical water at temperatures above 350 °C and in presence of alkaline conditions.Sawicki J.A. (2011) Hydrothermal synthesis of Ni₂FeBO₅ in near-supercritical PWR coolant and possible effects of neutron-induced 10^B fission in fuel crud. Journal of Nuclear Materials. 415, p 179-188. Zs Rak, CJ O'Brien, Dongwon Shin, Anders David Andersson, CR Stanek, DW Brenner (2016) Theoretical assessment of bonaccordite formation in pressurized water reactors. Journal of Nuclear Materials, 474, p. 62-64. Its formation in PWR reactors can be accelerated by lithium produced in ¹⁰B(n,α)⁷Li reaction with boron in coolant. Bonaccordite can be an indicator of Axial-Offset-Anomaly of neutron flux and power density in PWR power plants.

References

{{Reflist Nickel minerals Iron(III) minerals Borate minerals Orthorhombic minerals Minerals in space group 55 Minerals described in 1974