Jakobssonite, CaAlF₅, a new mineral from fumaroles at the Eldfell and Hekla volcanoes, Iceland

Abstract

The new mineral jakobssonite, ideally CaAlF5, 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 μm long. Its calculated density is 2.89 g cm–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 (Ca0.73Mg0.09Na0.02)Σ0.84Al1.06F4.09(OH)1.01. Jakobssonite is monoclinic, space group C2/c, with a = 8.601(1), b = 6.2903(6), c = 7.2190(7) Å, β = 114.61(1)o, V = 355.09(8) Å3and Z = 4. The crystal structure contains chains of [AlF6] octahedra which run parallel to the c axis. These chains are interconnected by chains of [CaF7] pentagonal bipyramids. Jakobssonite is isostructural with several other CaMIIIF5 compounds. The eight strongest lines in the powder diffraction diagram [d in Å (I) (hkl)] are as follows: 4.91 (18) (110), 3.92 (76) (200), 3.15 (68) (020), 3.13 (100) (11̄2̄), 2.27 (22) (22̄2̄), 1.957 (21) (400), 1.814 (20) (13̄2̄), 1.805 (22) (204̄). The chemical and crystal-structure analyses of jakobssonite are similar to synthetic CaAlF5 with minor substitutions of light elements (e.g. Na) or vacancies for Ca, and OH for F.

Balićžunićite, Bi2O(SO4)2, a new fumarole mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy

“…crystal-structure determination from singlecrystal and powder techniques and the theoretical crystal-chemistry of minerals) including applications in material science, nano-science, minerogenesis and petrogenesis, research into environmental hazards and biomineralogy. His particular interest in volcanic sublimates led him to contribute to the discovery of a number of new mineral species from fumarole deposits: kudriavite (Chaplygin et al, 2005), mutnovskyite (Zelenski et al, 2006), eldfellite (Balić-Ž unić et al, 2009), heklaite (Garavelli et al, 2010), jakobssonite (Balić-Ž unić et al, 2012), leonardsenite and oskarssonite (Jacobsen et al, 2013).…”

Sol-Gel-Synthesis of Nanoscopic Complex Metal Fluorides

“…Powder diffraction measurements and 19 F MAS NMR spectroscopy were performed to confirm the crystal structure of CaAlF 5 [30,31,32] and Ca 2 AlF 7 [32,33,34,35]. Both crystal structures correspond to those found in the naturally occurring phases in Jakobssonite [36] (CaAlF 5 ) and Carlhintzeite [37] (Ca 2 AlF 7 ∙H 2 O), respectively. However, to the best of our knowledge, no synthetic phase of CaAl 2 F 8 , which occurs in Prosopite (CaAl 2 (F,OH) 8 ), has been reported so far.…”

Verneite, Na2Ca3Al2F14, a New Aluminum Fluoride Mineral from Icelandic and Vesuvius Fumaroles

“…The geological settings and a description of the Hekla and Eldfell fumaroles where the new mineral was found are given in the papers mentioned in the Introduction [1][2][3][4][5][6][7]. Recently, the mineral has also been identified in samples originating from fumaroles on Fimmvörduhlas, Iceland, active during and after the eruption in 2010 [8].…”

“…In the crystal structures with CN6, the coordination is in the form of a nearly perfect octahedron (in colquirite [19]) or subsequently more distorted octahedra in Na 4 Ca 4 Al 7 F 33 [20], β-NaCaAlF 6 [20], and KCaAl 2 F 9 [21]. Ca with CN7 appears in moderately distorted pentagonal bipyramids in jakobssonite [4,22] and Ca 2 AlF 7 (Ca1) [23]. A regular pentagonal bipyramid is the maximum-volume polyhedron for CN7 and the υ values are calculated in comparison with it.…”

“…The new mineral verneite, Na 2 Ca 3 Al 2 F 14 , was discovered among sublimates collected from fumaroles on the Eldfell and Hekla volcanoes, where a considerable number of new fumarolic minerals has been observed [1]; six of them have so far been fully described [2][3][4][5][6][7]. The same mineral phase was identified at approximately the same time in a sublimate sample from Vesuvius, belonging to the Pelloux collection, which is stored in the mineralogical section of the Museum of Earth Sciences at Bari University.…”