Bonaccordite

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

Bonaccordite
Bonaccordite (brown) with trevorite (green)
General
CategoryBorates
Formula
(repeating unit)		Ni2FeBO5
IMA symbolBna[1]
Strunz classification6.AB.30
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPbam
Identification
References[2][3]

History

Bonaccordite was first described in 1974 for an occurrence in the Bon Accord area, Barberton, Transvaal, South Africa.[3] It occurs in a tabular nickeliferous serpentinite, on the margin of an ultramafic intrusive.[3] The actual site of the bonaccordite finding is a possible meteorite site three kilometers west of the Scotia talc mine.[4]

Composition

The chemical formula for bonaccordite is Ni2FeBO5.[4]

Table 1. Chemical data of bonaccordite[4]
Fe2O 31.9%
NiO 52.7%
MgO 0.5%
MnO 0.04%
CaO 1.5%
SiO2 0.4%
B2O3 13.1%
Total 100.44%

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.[4][5] Bonaccordite usually occurs along with trevorite, liebenbergite, népouite, nimite, gaspeitev, and millerite in the area of Bon Accord.[6] All of these minerals crystallize as slender prisms.

Physical properties

Bonaccordite is an opaque mineral with a reddish-brown color.[4] In reflected light, the color is grey with a brownish tinge with strong, reddish-brown internal reflections.[4] In many cases, bonaccordite crystallizes into long, slender cylinders.[7] It has been discovered to be the nickel analogue of ludwigite.[4]

The Mohs hardness for bonaccordite is 7 and its density is 5.17 g/cm3.[7] The optical class is biaxial.[4] Bonaccordite has an orthorhombic crystal system with a point group of 2/m 2/m 2/m. The crystals are structured as elongated prisms within another material.[4] 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.[4]

Bonaccordite is insoluble and has only shown reactivity to hydrochloric acid. It is very hard to clean it off of fuel rods in nuclear power reactors where it is sometimes formed.[7][8] It has been shown to form hydrothermally in near-supercritical water at temperatures above 350 °C and in presence of alkaline conditions.[9][10] Its formation in PWR reactors can be accelerated by lithium produced in 10B(n,α)7Li reaction with boron in coolant.[9] Bonaccordite can be an indicator of Axial-Offset-Anomaly of neutron flux and power density in PWR power plants.[9][10]

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Mindat.org entry
  3. Webmineral data
  4. Handbook of Mineralogy
  5. 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
  6. Fleischer M., Cabri L. (1976) New Mineral Names. American Mineralogist. 61, P 502-504.
  7. Deshon J. (2003) Advisory Committee on Reactor Safeguards Reactor Fuels Subcommittee - Open Session. United States of America Nuclear Regulatory Committee.
  8. 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.
  9. Sawicki J.A. (2011) Hydrothermal synthesis of Ni2FeBO5 in near-supercritical PWR coolant and possible effects of neutron-induced 10B fission in fuel crud. Journal of Nuclear Materials. 415, p 179-188.
  10. 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.
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