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Russoite, NH (sub 4) ClAs (sub 2) (super 3+) O (sub 3) (H (sub 2) O) (sub 0.5) , a new phylloarsenite mineral from Solfatara Di Pozzuoli, Napoli, Italy

Italo Campostrini, Francesco Demartin and Marco Scavini
Russoite, NH (sub 4) ClAs (sub 2) (super 3+) O (sub 3) (H (sub 2) O) (sub 0.5) , a new phylloarsenite mineral from Solfatara Di Pozzuoli, Napoli, Italy
Mineralogical Magazine and Journal of the Mineralogical Society (February 2019) 83 (1): 89-94

Abstract

The new mineral russoite (IMA2015-105), NH (sub 4) ClAs (sub 2) (super 3+) O (sub 3) (H (sub 2) O) (sub 0.5) , was found at the Solfatara di Pozzuoli, Pozzuoli, Napoli, Italy, as a fumarolic phase associated with alacranite, dimorphite, realgar, mascagnite, salammoniac and an amorphous arsenic sulfide. It occurs as hexagonal plates up to approximately 300 mu m in diameter and 15 mu m thick, in rosette-like intergrowths. On the basis of powder X-ray diffraction measurements and chemical analysis, the mineral was recognised to be identical to the corresponding synthetic phase NH (sub 4) ClAs (sub 2) O (sub 3) (H (sub 2) O) (sub 0.5) . Crystals are transparent and colourless, with vitreous lustre and white streak. Tenacity is brittle and fracture is irregular. Cleavage is perfect on {001}. The measured density is 2.89(1) g/cm (super 3) ; the calculated density is 2.911 g/cm (super 3) . The empirical formula, (based on 4.5 anions per formula unit) is [(NH (sub 4) ) (sub 0.94) ,K (sub 0.06) ] (sub Sigma 1.00) (Cl (sub 0.91) ,Br (sub 0.01) ) (sub Sigma 0.92) As (sub 2.02) O (sub 3) (H (sub 2) O) (sub 0 .5) . Russoite is hexagonal, space group P622, with a = 5.2411(7), c = 12.5948(25) Aa, V = 299.62(8) A (super 3) and Z = 2. The eight strongest X-ray powder diffraction lines are [dobs A(I)(hkl)]: 12.63(19)(001), 6.32(100)(002), 4.547(75)(100), 4.218(47)(003), 3.094(45)(103), 2.627(46)(110), 2.428(31)(112) and 1.820(28)(115). The structure, was refined to R = 0.0518 for 311 reflections with I > 2sigma (I) and shows a different location of the ammonium cation and water molecules with respect to that reported for the synthetic analogue. The mineral belongs to a small group of phylloarsenite minerals (lucabindiite, torrecillasite and gajardoite). It contains electrically neutral As (sub 2) O (sub 3) layers, topologically identical to those found in lucabindiite and gajardoite between which are ammonium cations and outside of which Cl (super -) anions. Water molecules and additional ammonium cations are located in a layer between two levels of chloride anions.


ISSN: 0369-0148
Coden: MNLMBB
Serial Title: Mineralogical Magazine and Journal of the Mineralogical Society
Serial Volume: 83
Serial Issue: 1
Title: Russoite, NH (sub 4) ClAs (sub 2) (super 3+) O (sub 3) (H (sub 2) O) (sub 0.5) , a new phylloarsenite mineral from Solfatara Di Pozzuoli, Napoli, Italy
Affiliation: Universita degli Studi di Milano, Dipartimento di Chimica, Milan, Italy
Pages: 89-94
Published: 201902
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 21
Accession Number: 2019-026983
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
N40°49'60" - N40°49'60", E14°07'60" - E14°07'60"
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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