IMA 2015-105 = russoite

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Marco E. Ciriotti
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IMA 2015-105 = russoite

Messaggio da Marco E. Ciriotti » ven 18 mag, 2018 18:14

Prossima pubblicazione.

Referenza:
▪ Campostrini, I., Demartin, F., Scavini, M. (2018): Russoite, NH4ClAs3+2O3(H2O)0.5, a new phylloarsenite mineral from Solfatara di Pozzuoli, Napoli, Italy. Mineralogical Magazine, 82, (in press).
Marco E. Ciriotti

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TOSATO FABIO
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Re: IMA 2015-105 = russoite

Messaggio da TOSATO FABIO » sab 19 mag, 2018 9:35

COMPLIMENTI A TUTTI.
Tosato Fabio
"Il vero viaggio di scoperta non consiste nel cercare nuove terre, ma nell'avere nuovi occhi." M. Proust
Noi siamo anche quello che non siamo riusciti ad essere.
Sic transit gloria mundi.

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Marco E. Ciriotti
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Re: IMA 2015-105 = russoite

Messaggio da Marco E. Ciriotti » sab 10 nov, 2018 12:07

Referenza:
▪ Campostrini, I., Demartin, F., Scavini, M. (2019): Russoite, NH4ClAs3+2O3(H2O)0.5, a new phylloarsenite mineral from Solfatara di Pozzuoli, Napoli, Italy. Mineralogical Magazine, 83, (in press).

Abstract:
The new mineral russoite (IMA 2015-105), NH4ClAs3+2O3(H2O)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 about 300 μm in diameter and 15 μm thick, in rosette-like intergrowths. On the basis of PXRD measurements and chemical analysis, the mineral was recognized to be identical to the corresponding synthetic phase NH4ClAs2O3(H2O)0.5. Crystals are transparent and colorless, 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/cm3, the calculated density is 2.911 g/cm3. The empirical formula, (based on 4.5 anions pfu) is [(NH4)0.94,K0.06]Σ1.00(Cl0.91,Br0.01)Σ0.92As2.02O3(H2O)0.5. Russoite is hexagonal, space group P622, with a = 5.2411(7), c = 12.5948(25) Å, V = 299.62(8) Å3 and Z = 2. The eight strongest X-ray powder diffraction lines are [dobs Å(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 >2(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, gajardoite). It contains electrically neutral As2O3 layers, topologically identical to those found in lucabindiite and gajardoite between which are ammonium cations and outside of which Cl- anions. Water molecules and additional ammonium cations are located in a layer between two levels of chloride anions.
Marco E. Ciriotti

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Marco E. Ciriotti
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Re: IMA 2015-105 = russoite

Messaggio da Marco E. Ciriotti » gio 14 mar, 2019 9:44

Pubblicazione effettuata.

Referenza:
▪ Campostrini, I., Demartin, F., Scavini, M. (2019): Russoite, NH4ClAs3+2O3(H2O)0.5, a new phylloarsenite mineral from Solfatara di Pozzuoli, Napoli, Italy. Mineralogical Magazine, 83, 89-94.

Abstract:
The new mineral russoite (IMA 2015-105), NH4ClAs3+2O3(H2O)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 about 300 μm in diameter and 15 μm thick, in rosette-like intergrowths. On the basis of PXRD measurements and chemical analysis, the mineral was recognized to be identical to the corresponding synthetic phase NH4ClAs2O3(H2O)0.5. Crystals are transparent and colorless, 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/cm3, the calculated density is 2.911 g/cm3. The empirical formula, (based on 4.5 anions pfu) is [(NH4)0.94,K0.06]Σ1.00(Cl0.91,Br0.01)Σ0.92As2.02O3(H2O)0.5. Russoite is hexagonal, space group P622, with a = 5.2411(7), c = 12.5948(25) Å, V = 299.62(8) Å3 and Z = 2. The eight strongest X-ray powder diffraction lines are [dobs Å(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 >2(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, gajardoite). It contains electrically neutral As2O3 layers, topologically identical to those found in lucabindiite and gajardoite between which are ammonium cations and outside of which Cl- anions. Water molecules and additional ammonium cations are located in a layer between two levels of chloride anions.
Marco E. Ciriotti

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Marco E. Ciriotti
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Re: IMA 2015-105 = russoite

Messaggio da Marco E. Ciriotti » gio 08 giu, 2023 10:42

Un recente lavoro sull'analogo sintetico indica un gruppo spaziale diverso.

Referenza:
▪ Wrześniewska, W., Paluch, P., Guńka, P.A. (2023): Arsenic(III) oxide intercalate with ammonium chloride: crystal structure revision and thermal characterization. Acta Crystallographica, B79, 207-212.

Abstract:
According to the crystal structure determination by Edstrand & Blomqvist [Ark. Kemi (1955), 8, 245–256], intercalate NH4Cl·As2O3·0.5H2O (YNH4Cl) is not isostructural with compound KCl·As2O3·0.5H2O. This is very unlikely because both NH4Br·2As2O3 and KBr·2As2O3 as well as NH4I·2As2O3 and KI·2As2O3 are isostructural. Hence, intercalate YNH4Cl has been studied using single-crystal X-ray diffraction in addition to attenuated total reflection Fourier transform infrared (ATR-FTIR) and 15N solid-state magic-angle spinning nuclear magnetic resonance (ssNMR) spectroscopies. These techniques indicate that revising the previous crystal structure model is necessary. Compound YNH4Cl crystallizes in space group P6/mmm with unit-cell parameters a = 5.25420 (10) Å and c = 12.6308 (3) Å and is isostructural with KCl·As2O3·0.5H2O. The presence of two symmetry-independent ammonium cations in the structure has been unequivocally confirmed using 15N ssNMR spectroscopy. The 15N ssNMR spectrum of intercalate YNH4Cl has been compared with analogous spectra of NH4Br·2As2O3 and NH4I·2As2O3 which allowed for a probable assignment of signals to ammonium cations occupying particular sites in the crystal structures. Thermogravimetry, differential scanning calorimetry and variable-temperature ATR-FTIR spectra have revealed that intercalate YNH4Cl is dehydrated between 320 and 475 K. Upon cooling or standing in moist air water is re-absorbed. Dehydration leads to significant shortening of the c unit-cell parameter as revealed by powder X-ray diffraction [c = 12.1552 (7) Å at 293 K]. Compound YNH4Cl decomposes on prolonged heating above 490 K to arsenic(III) oxide and ammonium chloride.
Marco E. Ciriotti

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Marco E. Ciriotti
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Re: IMA 2015-105 = russoite

Messaggio da Marco E. Ciriotti » ven 09 giu, 2023 10:10

La lettura del lavoro degli autori polacchi (messaggio precedente) lascia quasi intendere che non abbiano letto la descrizione-tipo della russoite. Il modo di citarne l'esistenza è del tutto incompleto.
Che una fase minerale possa trovare risposta diffrattiva in più di un gruppo spaziale è del tutto normale. Che un sintetico permetta, di norma, un raffinamento migliore ça va sans dire.
Il gruppo spaziale della fase naturale, russoite, ha permesso il miglior raffinamento nel gruppo spaziale P622.
Probabilmente se gli autori polacchi avessero analogamente provato il raffinamento nel gruppo spaziale P622 avrebbero ottenuto un risultato migliore.
Marco E. Ciriotti

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