Extremely Al-depleted chlorites from dolomite carbonatites of the Kovdor ultramafic-alkaline complex, Kola Peninsula, Russia

Chukanov, N.V.; Krzhizhanovskaya, M.G.; Pekov, I.V.; Varlamov, D.A.; Van K, V.; Ermolaeva, V.N.; Vozchikova, S.A.

Авторы: Chukanov N.V., Krzhizhanovskaya M.G., Pekov I.V., Varlamov D.A., Van K V., Ermolaeva V.N., Vozchikova S.A.
Журнал: Clays and Clay Minerals
Том: 68
Номер: 1
Год издания: 2020
Издательство: The Clay Minerals Society
Местоположение издательства: United States
Первая страница: 81
Последняя страница: 88
DOI: 10.1007/s42860-019-00055-8
Аннотация: The problem to be solved is whetherAl is a necessary component of Fe-Mg chlorites. Very unusual Al-depleted and Fe-enriched trioctahedral chloriteswith the empirical formulae Na0.05Ca0.05(Fe2+3.01Mg2.01Ti0.14Fe3+0.04)Σ6.00[(Si3.53Fe3+0.41Al0.06)Σ4.00O10](OH)8·nH2O (Sample 1) and Na0.05Ca0.01(Fe2+3.26Mg1.97Fe3+0.75Mn0.01Ti0.01)Σ6.00[(Si3.16Fe3+0.75Al0.09)Σ4.00O10](OH)8 (Sample 2) have been discovered in Al-depleted dolomite carbonatites of the Kovdor complex of ultramafic, alkaline rocks and carbonatites, Kola Peninsula, Russia. The presence of substantial amounts of Ti in Sample 1 is another unusual feature of this mineral. In both samples, chlorites are intimately intergrown with cronstedtite-1T which is an indication of a low stability of chlorite structure in the absence of aluminum in the tetrahedral sheet. The crystal structure of chlorite in Sample 1 was solved by the Rietveld method. The mineral is triclinic (IIb-4-module), space group C-1, a = 5.4153(4), b = 9.3805(7), c = 14.5743(12) Å,α= 90.137(5)°,β= 96.928(5)°, γ = 90.043(6)°, V = 734.95(10)Å3, andZ=2.A problem to be solved is how stable are Al-free chlorites belonging to the clinochlore–chamosite solid-solution series and whether their existence in natural mineral assemblages is possible. The results obtained indicate that even though Al-depleted chlorites belonging to the clinochlore–chamosite solid-solution series exist in Nature as metastable phases, these minerals are extremely rare and much less stable than Al-poor serpentines.
Добавил в систему: Пеков Игорь Викторович

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Extremely Al-depleted chlorites from dolomite carbonatites of the Kovdor ultramafic-alkaline complex, Kola Peninsula, Russiaстатья Исследовательская статья

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