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Heklaite, KNaSiF6, a new fumarolic mineral from Hekla volcano, Iceland

Published online by Cambridge University Press:  05 July 2018

A. Garavelli ,
T. Balić-Žunić ,
D. Mitolo ,
P. Acquafredda ,
E. Leonardsen  and
S. P. Jakobsson
A. Garavelli*
Affiliation:
Dipartimento Geomineralogico, Università di Bari, via E. Orabona 4, I–70125 Bari, Italy
T. Balić-Žunić
Affiliation:
Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 København K, Denmark
D. Mitolo
Affiliation:
Dipartimento Geomineralogico, Università di Bari, via E. Orabona 4, I–70125 Bari, Italy
P. Acquafredda
Affiliation:
Dipartimento Geomineralogico, Università di Bari, via E. Orabona 4, I–70125 Bari, Italy
E. Leonardsen
Affiliation:
St. Karlsmindevej 46, DK-3390 Hundested, Denmark
S. P. Jakobsson
Affiliation:
Icelandic Institute of Natural History, Hlemmur 3, P.O. Box 5320, IS-125 Reykjavik, Iceland
*
*E-mail: a.garavelli@geomin.uniba.it
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Abstract

Heklaite, with the ideal formula KNaSiF6, was found among fumarolic encrustations collected in 1992 on the Hekla volcano, Iceland. Heklaite forms a fine-grained mass of micron- to sub-micron-sized crystals intimately associated with malladrite, hieratite and ralstonite. The mineral is colourless, transparent, non-fluorescent, has a vitreous lustre and a white streak. The calculated density is 2.69 g cm–3. An SEM-EDS quantitative chemical analysis shows the following range of concentrations (wt.%): Na 11.61–12.74 (average 11.98), K 17.02–18.97 (average 18.29), Si 13.48 –14.17 (average 13.91), F 54.88–56.19 (average 55.66). The empirical chemical formula, calculated on the basis of 9 a.p.f.u., is Na1.07K0.96Si1.01F5.97. X-ray powder diffraction indicates that heklaite is orthorhombic, space group Pnma, with the following unit-cell parameters: a = 9.3387(7) Å, b = 5.5032(4) Å, c = 9.7957(8) Å , V = 503.43(7) Å3, Z = 4. The eight strongest reflections in the powder diffraction pattern [d in Å (I/I0) (hkl)] are: 4.33 (53) (102); 4.26 (56) (111); 3.40 (49) (112); 3.37 (47) (202); 3.34 (100) (211); 2.251 (27) (303); 2.050 (52) (123); 2.016 (29) (321). On the basis of chemical analyses and X-ray data, heklaite corresponds to the synthetic compound KNaSiF6. The name is for the type locality, the Hekla volcano, Iceland.

Keywords

heklaitenew mineralsublimatesfumarolesfluorosilicatecrystal structureHeklaIceland
Type
Research Article
Information
Mineralogical Magazine , Volume 74 , Issue 1 , February 2010 , pp. 147 - 157
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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