On the application of the IMA-CNMNC dominant-valency rule to complex mineral compositions

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Marco E. Ciriotti
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On the application of the IMA-CNMNC dominant-valency rule to complex mineral compositions

Messaggio da Marco E. Ciriotti » ven 23 ago, 2019 11:06

Prossima pubblicazione.

Referenza:
▪ Bosi, F., Hatert, F., Hålenius, U., Pasero, M., Miyawaki, R., Mills, S.J. (2019): On the application of the IMA-CNMNC dominant-valency rule to complex mineral compositions. Mineralogical Magazine, 83, (in press).

Abstract:
Mineral species should be identified by an end-member formula and by using the dominant-valency rule as recommended by the IMA-CNMNC. However, the dominant-end-member approach has also been used in the literature. These two approaches generally converge, but for some intermediate compositions, significant differences between the dominant-valency rule and the dominant end-member approach can be observed. As demonstrated for garnet-supergroup minerals, for example, the end-member approach is ambiguous, since end-member proportions strongly depend on the calculation sequence. For this reason, the IMA-CNMNC strongly recommends the use of the dominant-valency rule for mineral nomenclature, because it alone may lead to unambiguous mineral identification. Although the simple application of the dominant-valency rule is successful for the identification of many mineral compositions, sometimes it leads to unbalanced end-member formulae, due to the occurrence of a coupled heterovalent substitution at two sites along with a heterovalent substitution at a single site. In these cases, it may be useful to use the site-total-charge approach to identify the dominant root-charge arrangement on which to apply the dominant-constituent rule. The dominant-valency rule and the site-total-charge approach may be considered two procedures complementary to each other for mineral identification. Their critical point is to find the most appropriate root-charge and atomic arrangements consistent with the overriding condition dictated by the end-member formula. These procedures were approved by the IMA−CNMNC in May 2019.

NdR: Superbo articolo (bravo Ferdinando!) e molto apprezzabile la velocità (davvero insolita) con cui si andrà alla pubblicazione.
Si tratta di un importantissimo lavoro che permetterà (previa approvazione da parte dell'IMA CNMNC) di correggere alcuni errori e soprattutto eviterà di farne molti altri.
Se qualcuno è interessato all'intero testo non ha che da chiedermelo: m.ciriotti@tin.it.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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