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Sbacchiite, Ca (sub 2) AlF (sub 7) , a new fumarolic mineral from the Vesuvius Volcano, Napoli, Italy

Italo Campostrini, Francesco Demartin and Massimo Russo
Sbacchiite, Ca (sub 2) AlF (sub 7) , a new fumarolic mineral from the Vesuvius Volcano, Napoli, Italy
European Journal of Mineralogy (September 2018) 31 (1): 153-158


The new mineral sbacchiite (IMA 2017-097), Ca (sub 2) AlF (sub 7) , was found in a fossil fumarole (1944 eruption, T nearly equal 80 degrees C) at the rim of the crater of the Vesuvius volcano, Napoli, Italy, associated with gearsksutite, usovite, creedite and opal. It forms elongated crystals up to about 60 mu m in length. On the basis of powder X-ray diffraction data and chemical analysis, the mineral was recognized to be identical to the corresponding synthetic phase. Crystals are transparent or translucent and colourless, with vitreous lustre and white streak. The tenacity is brittle. The measured density is 3.08(2) g/cm (super 3) , the calculated density is 3.116 g/cm (super 3) . The empirical formula, (based on 10 atoms per formula unit, apfu) is Ca (sub 2.02) Mg (sub 0.03) Al (sub 0.99) F (sub 6.97) . Sbacchiite is orthorhombic, space group Pnma, with a = 7.665(2), b = 6.993(1), c = 9.566(2) Aa, V = 512.2(2) Aa (super 3) and Z = 4. The eight strongest X-ray powder diffraction lines are [d (sub obs) Aa(I)(hkl)]: 3.840(45)(200), 3.563(85)(201), 3.499(100)(020), 2.899(55)(013), 2.750(30)(212), 2.281(20)(104), 2.255(52)(302) and 2.173(36)(131). The structure was refined to R = 0.0479 for 457 reflections with I > 2sigma (I). The asymmetric unit contains one Al (super 3+) and two independent Ca (super 2+) cations and five fluorine anions. Aluminium is octahedrally coordinated by six fluorine atoms; the arrangement of F around the 7-coordinated Ca(1) conforms to a distorted pentagonal bipyramid and that around Ca(2) to a very distorted polyhedron (in 7 + 1 coordination). All the fluorine atoms are threefold coordinated. The structure framework shows "isolated" [AlF (sub 6) ] octahedra, whereas the coordination polyhedra around Ca are linked by common edges [sequence: Ca(1)-Ca(2)-Ca(1)...] along [010] and the same holds for the connection along [001]. Along [100], however, only the pentagonal bipyramids around Ca(1) are connected by bridging corners.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 31
Serial Issue: 1
Title: Sbacchiite, Ca (sub 2) AlF (sub 7) , a new fumarolic mineral from the Vesuvius Volcano, Napoli, Italy
Affiliation: Universita degli Studi di Milano, Dipartimento di Chimica, Milan, Italy
Pages: 153-158
Published: 20180906
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 25
Accession Number: 2018-099128
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
N40°49'22" - N40°49'22", E14°25'44" - E14°25'44"
Secondary Affiliation: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli, ITA, Italy
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201852
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