Discreditation of ‘marshallsussmanite’ and reinstatement of the name schizolite

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Marco E. Ciriotti
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Discreditation of ‘marshallsussmanite’ and reinstatement of the name schizolite

Messaggio da Marco E. Ciriotti » mar 23 apr, 2019 20:49

Prossima pubblicazione.

Referenza:
▪ Grice, J.D., Lussier, A.J., Friis, H., Rowe, R., Poirier, G.G., Fihl, Z. (2019): Discreditation of the pyroxenoid mineral name ‘marshallsussmanite’ with a reinstatement of the name schizolite MnCaMnSi3O8(OH). Mineralogical Magazine, 83, (in press).

Abstract:
Schizolite, originating from the type locality, Tutop Agtakôrfia, in the Ilímaussaq alkaline complex, Julianehåb district, South Greenland, was initially described by Winther (1901) with additional data being supplied by Bøggild (1903). Recently, a proposal for the new mineral ‘marshallsussmanite’ was submitted to, and approved by, the International Mineralogical Association - Commission on New Minerals, Nomenclature, and Classification (IMA 2013-067) by Origlieri et al. (2013). Results from the detailed examination of two schizolite cotype samples presented here, using single-crystal XRD, powder XRD, and optics, confirms it be equivalent to ‘marshallsussmanite’. Historical precedence sets a priority for discrediting the name ‘marshallsussmanite’ in favour of the original, more-than-a century-old name, schizolite. The two schizolite samples investigated vary slightly in physical and chemical properties but are consistent overall. The prismatic crystals are pale red or pink to brownish. Schizolite is brittle with a splintery aspect. It is biaxial positive, with average optical parameters: α = 1.626 ± 0.003, β = 1.630 ± 0.002, γ = 1.661 ± 0.002, 2Vmeas = 71(4)º and 2Vcalc = 40º; there is no pleochroism. Electron microprobe analysis shows both samples have nearly identical compositions (differences < 0.4 wt. % oxide), with the mean values of: SiO2, 52.6(4); Al2O3, 0.005(1); FeO, 2.54(2); MnO, 13.86(9); CaO, 17.9(4); Na2O 8.9(1); H2O, 2.59(2) wt. % oxide; this corresponds to a mean formula of: Na1.00(2)Ca1.11(7)Mn0.68(1) Fe0.12(0)Si3.041(1)O8(OH). Final least-squares structure refinements for both samples converged at R1-values ≤2 .0%; H atoms were located in all refinements.
Marco E. Ciriotti

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