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How many alacranites do exist? A structural study of non-stoichiometric As (sub 8) S (sub 9-X) crystals

Paola Bonazzi, Luca Bindi, Filippo Olmi and Silvio Menchetti
How many alacranites do exist? A structural study of non-stoichiometric As (sub 8) S (sub 9-X) crystals (in Special issue dedicated to the memory of Luciano Ungaretti, Maria Chiara Domeneghetti (prefacer))
European Journal of Mineralogy (April 2003) 15 (2): 283-288

Abstract

Crystals of arsenic sulphide (reported as alacranite), coming from the burning dump of Katerina Mine (Czech Republic), have been investigated by single crystal X-ray diffraction and chemical microanalysis. Both analytical data and unit-cell parameters strongly suggest the existence of a continuous series between the high-temperature polymorph (beta -As (sub 4) S (sub 4) ) and the mineral alacranite (As (sub 8) S (sub 9) ). As the S content increases in the series, the unit-cell volume increases accordingly. The structural model has been obtained for two crystals, exhibiting different unit-cell volumes (ALA15: a = 9.940(2), b = 9.398(2), c = 9.033(2), beta =102.12(2), V = 825.0(3), R (sub obs) = 6.12 %; ALA2: a = 9.936(2), b = 9.458(2), c = 9.106(2), = 101.90(2), V = 837.3(3), R (sub obs) = 6.41 %). We found that the non-stoichiometric compounds crystallize as a disordered mixture of two kinds of cage-like molecules, packed together as in the beta -As (sub 4) S (sub 4) phase. The first one is identical to the As (sub 4) S (sub 4) molecule found in the structures of both realgar (alpha -As (sub 4) S (sub 4) ) and beta -As (sub 4) S (sub 4) . The second molecule is chemically and structurally identical to that found in the As (sub 4) S (sub 5) compound. The simultaneous presence of As (sub 4) S (sub 4) (C2/c) and As (sub 8) S (sub 9) (P2/c) microdomains could be a reason for the observed gradual change of the translation symmetry from the beta -phase to alacranite s.s..


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 15
Serial Issue: 2
Title: How many alacranites do exist? A structural study of non-stoichiometric As (sub 8) S (sub 9-X) crystals
Title: Special issue dedicated to the memory of Luciano Ungaretti
Author(s): Bonazzi, PaolaBindi, LucaOlmi, FilippoMenchetti, Silvio
Author(s): Domeneghetti, Maria Chiaraprefacer
Affiliation: Universita di Firenze, Dipartimento di Scienze della Terra, Florence, Italy
Pages: 283-288
Published: 200304
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 23
Accession Number: 2003-032470
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
N48°34'60" - N51°02'60", E12°22'60" - E18°53'60"
Secondary Affiliation: CNR Istituto di Geoscienze e Georisorse-Sezione di Firenze, ITA, Italy
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200311
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