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Jakobssonite, CaAlF (sub 5) , a new mineral from fumaroles at the Eldfell and Hekla volcanoes, Iceland

T. Balic-Zunic, A. Garavelli, D. Mitolo, P. Acquafredda and E. Leonardsen
Jakobssonite, CaAlF (sub 5) , a new mineral from fumaroles at the Eldfell and Hekla volcanoes, Iceland
Mineralogical Magazine (June 2012) 76 (3): 751-760


The new mineral jakobssonite, ideally CaAlF (sub 5) , was first found in crusts collected in 1988 from a fumarole on the Eldfell volcano, Heimaey Island, Iceland. It was subsequently found in similar crusts collected in 1991 from a fumarole on the Hekla volcano, Iceland. It is associated with leonardsenite (IMA2011-059), ralstonite, heklaite, anhydrite, gypsum, jarosite, hematite, opal and several fluoride minerals that have not been fully characterized. Jakobssonite occurs as soft white fragile crusts of acicular crystals <50 mu m long. Its calculated density is 2.89 g cm (super -3) . Chemical analyses by energy-dispersive spectrometry on a scanning electron microscope produced a mean elemental composition as follows: Ca, 18.99; Al, 18.55; Mg, 1.33; Na, 0.33; F, 50.20; O, 10.39; total 99.79 wt.%. The empirical chemical formula, calculated on the basis of 7 atoms per formula unit with all of the oxygen as OH, is (Ca (sub 0.73) Mg (sub 0.09) Na (sub 0.02) ) (sub Sigma 0.84) Al (sub 1.06) F (sub 4.09) (OH) (sub 1.01) . Jakobssonite is monoclinic, space group C2/c, with a = 8.601(1), b = 6.2903(6), c = 7.2190(7) Aa, beta = 114.61(1) (super o) , V = 355.09(8) Aa (super 3) and Z = 4. The crystal structure contains chains of [AlF (sub 6) ] octahedra which run parallel to the c axis. These chains are interconnected by chains of [CaF (sub 7) ] pentagonal bipyramids. Jakobssonite is isostructural with several other CaM (super III) F (sub 5) compounds. The eight strongest lines in the powder diffraction diagram [d in Aa (I) (hkl)] are as follows: 4.91 (18) (110), 3.92 (76) (200), 3.15 (68) (020), 3.13 (100) (11i2i), 2.27 (22) (22i2i), 1.957 (21) (400), 1.814 (20) (13i2i), 1.805 (22) (204i). The chemical and crystal-structure analyses of jakobssonite are similar to synthetic CaAlF (sub 5) with minor substitutions of light elements (e.g. Na) or vacancies for Ca, and OH for F.

ISSN: 0026-461X
EISSN: 1471-8022
Serial Title: Mineralogical Magazine
Serial Volume: 76
Serial Issue: 3
Title: Jakobssonite, CaAlF (sub 5) , a new mineral from fumaroles at the Eldfell and Hekla volcanoes, Iceland
Affiliation: Natural History Museum of Denmark, Copenhagen, Denmark
Pages: 751-760
Published: 201206
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 22
Accession Number: 2012-092182
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
N64°01'00" - N64°01'00", W19°38'60" - W19°38'60"
N63°25'58" - N63°25'58", W20°14'59" - W20°14'59"
Secondary Affiliation: Universita di Bari, ITA, Italy
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201248
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