Publication Type:

Journal Article

Authors:

Piilonen, Paula C.; Lalonde, Andre E.; McDonald, Andrew M.; Gault, Robert A.; Larsen, Alf Olav

Source:

The Canadian MineralogistThe Canadian Mineralogist, Mineralogical Association of Canada, Ottawa, ON, Canada, Volume 41, Part 1, p.1-26 (2003)

ISBN:

0008-4476

Keywords:

alkali granites, astrophyllite, Canada, chain silicates, chemical composition, Commonwealth of Independent States, crystal chemistry, crystal structure, crystal systems, eastern canada, enrichment, Europe, formula, geochemistry, granites, ICP mass spectra, igneous rocks, Khibiny Mountains, Lovozero Massif, mass spectra, Mont-Saint-Hilaire Quebec, Mossbauer spectra, Murmansk Russian Federation, nepheline syenite, nomenclature, oxidation, plutonic rocks, quebec, Rouville County Quebec, Russian Federation, samples, silicates, spectra, syenites, triclinic system

Abstract:

On the basis of EPMA, ICP-AES, FTIR, TG and Moessbauer spectroscopy for 135 samples of astrophyllite from 35 localities, a standardized general formula has been developed in the form A (sub 2) BC (sub 7) D (sub 2) T (sub 8) O (sub 26) (OH) (sub 4) X (sub 0-1) , where (super [10]-[13]) A = K, Rb, Cs, H (sub 2) O (super +) , H (sub 2) O, Na or []; (super [10]) B = Na or Ca; (super [6]) C = Mn, Fe (super 2+) , Fe (super 3+) , Na, Mg or Zn; (super [6]) D = Ti, Nb or Zr; (super [4]) T = Si or Al; X = phi = F, OH, O or []. F orders at the phi site and does not occur at the two general OH sites within the O sheet. On this basis, the formulae of the eight species of astrophyllite-group minerals have been redefined. Moessbauer spectroscopy indicates Fe (super 3+) /Fe (sub tot) values ranging from 0.01 to 0.21, corresponding with 0.05 to 0.56 pfu Fe (super 3+) , confirming that Fe (super 2+) is the dominant valence state for iron. Minerals from silica-oversaturated and undersaturated alkali intrusions are distinct in their chemical composition; in oversaturated rocks, astrophyllite sensu stricto occurs, a late stage post-magmatic phase enriched in Rb, Fe (super 2+) , Ti, Si and F, whereas undersaturated rocks show a great diversity in species. Kupletskite-subgroup samples are enriched in Na, Mn, Fe (super 3+) , Zn, Zr and Nb.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2004-022842<br/>astrophyllite group<br/>kupletskite