Reference:
▪ 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.
▪ 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.