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Acmonidesite, a new ammonium sulfate chloride from La Fossa Crater, Vulcano, Aeolian Islands, Italy

Francesco Demartin, Carlo Castellano and Italo Campostrini
Acmonidesite, a new ammonium sulfate chloride from La Fossa Crater, Vulcano, Aeolian Islands, Italy
Mineralogical Magazine and Journal of the Mineralogical Society (February 2019) 83 (1): 137-142

Abstract

The new mineral acmonidesite, (NH (sub 4) ,K,Pb (super 2+) ,Na) (sub 9) Fe (sub 4) (super 2+) (SO (sub 4) ) (sub 5) Cl (sub 8) , was found in an active fumarole (fumarole FA, temperature approximately 250 degrees C) at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs on a pyroclastic breccia as brown prismatic crystals up to 0.10 mm long, in association with salammoniac, alunite and adranosite. The mineral is orthorhombic, space group C2221 (no. 20) with a = 9.841(1), b = 19.448(3) c = 17.847(3) A, V = 3415.7(9) A (super 3) and Z = 4. The six strongest reflections in the powder X-ray diffraction pattern are: [d (sub obs) in A(I)(hkl)] 8.766(100)(110), 1.805(88)(390), 5.178(45)(131), 4.250(42)(221), 2.926(42)(330) and 2.684(32)(261). The empirical formula (based on 28 anions per formula unit [pfu]) is (NH (sub 4) ) (sub 5.77) K (sub 1.42) Pb (sub 0.62) Na (sub 1.24) Fe (sub 3.96) Mn (sub 0.08) S (sub 5.04) O (sub 20.16) Cl (sub 7. 97) Br (sub 0.08) . The idealised formula is (NH (sub 4) ,K,Pb (super 2+) ,Na) (sub 9) Fe (sub 4) (super 2+) (SO (sub 4) ) (sub 5) Cl (sub 8) . The calculated density is 2.551 g cm-3. Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.0363 for 4614 independent observed reflections [I > 2sigma (I)]. The structure contains two independent, distorted octahedral iron sites, Fe1 and Fe2, with the iron atoms in the 2+ oxidation state, as confirmed by the interatomic distances and bond-valence calculations (2.06 and 1.94 vu, respectively). Fe1 is surrounded by two chlorine atoms and four oxygens of the sulfate ions, with the following average distances (A): Fe1-O 2.125 and Fe1-Cl 2.472; and Fe2 is surrounded by three chlorine atoms and three oxygens of the sulfate ions, with the following average distances (A): Fe2-O 2.110 and Fe2-Cl 2.531. Three independent sulfate anions are also present and are connected with the iron polyhedra to form a three-dimensional structure containing voids occupied by four independent ammonium ions (two of them partially replaced by K (super +) ), one Na (super +) /Pb (super 2+) site and one Cl (super -) ion.


ISSN: 0369-0148
Coden: MNLMBB
Serial Title: Mineralogical Magazine and Journal of the Mineralogical Society
Serial Volume: 83
Serial Issue: 1
Title: Acmonidesite, a new ammonium sulfate chloride from La Fossa Crater, Vulcano, Aeolian Islands, Italy
Affiliation: Universita degli Studi di Milano, Dipartimento di Chimica, Milan, Italy
Pages: 137-142
Published: 201902
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 18
Accession Number: 2019-026988
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
N38°19'60" - N38°25'00", E14°52'00" - E15°00'00"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201915
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