2018/05/15 by I. Campostrini, Francesco Demartin, Marco Scavini · 2 citations
Materials Science · Chemistry · Environmental Science · #Crystal Structures and Properties #Crystal structures of chemical compounds #Chemical Synthesis and Characterization
paper · doi:10.1180/minmag.2017.081.097
openalex publication_date 2018/05/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/05/21
Abstract The new mineral russoite (IMA2015-105), NH 4 ClAs 2 3+ O 3 (H 2 O) 0.5 , was found at the Solfatara di Pozzuoli, Pozzuoli, Napoli, Italy, as a fumarolic phase associated with alacránite, dimorphite, realgar, mascagnite, salammoniac and an amorphous arsenic sulfide. It occurs as hexagonal plates up to ~300 µm in diameter and 15 µm 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 4 ClAs 2 O 3 (H 2 O) 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 3 ; the calculated density is 2.911 g/cm 3 . The empirical formula, (based on 4.5 anions per formula unit) is [(NH 4 ) 0.94 ,K 0.06 ] Σ1.00 (Cl 0.91 ,Br 0.01 ) Σ0.92 As 2.02 O 3 (H 2 O) 0.5 . Russoite is hexagonal, space group P 622, with a = 5.2411(7), c = 12.5948(25) Å, V = 299.62(8) Å 3 and Z = 2. The eight strongest X-ray powder diffraction lines are [ d obs 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 > 2σ( 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 2 O 3 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.