Torrecillasite, Na(As,Sb)₄³⁺O₆Cl, a new mineral from the Torrecillas mine, Iquique Province, Chile: description and crystal structure

Abstract

The new mineral torrecillasite (IMA2013-112), Na(As,Sb)43+O6Cl, was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, cinnabar, gypsum, halite, lavendulan, magnesiokoritnigite, marcasite, quartz, pyrite, scorodite, wendwilsonite and other potentially new As-bearing minerals. Torrecillasite occurs as thin colourless prisms up to 0.4 mm long in jack-straw aggregates, as very thin fibres in puff balls and as massive intergrowths of needles. Prisms are elongated on [100] with diamond-shaped cross-section and irregular terminations. Crystals are transparent, with adamantine lustre and white streak. The Mohs hardness is 2½, tenacity is brittle and fracture is irregular. Cleavage on (001) is likely. The calculated density is 4.056 g cm−3. Optically, torrecillasite is biaxial (−) with α = 1.800(5), β = 1.96(1), γ = 2.03(calc.) (measured in white light). The measured 2V is 62.1(5)°, no dispersion or pleochroism were observed, the optical orientation isX=c,Y=b,Z=a. The mineral is very slowly soluble in H2O, slowly soluble in dilute HCl and rapidly soluble in concentrated HCl. The empirical formula, determined from electron-microprobe analyses, is (Na1.03Mg0.02)∑1.05(As3.39Sb0.62)∑4.01O6.07Cl0.93. Torrecillasite is orthorhombic,Pmcn, a= 5.2580(9),b= 8.0620(13),c= 18.654(3) Å,V= 790.7(2) Å3andZ= 4. The eight strongest X-ray powder diffraction lines are [dobsÅ(I)(hkl)]: 4.298(33)(111), 4.031(78)(014,020), 3.035(100)(024,122), 2.853(39)(115,123), 2.642(84)(124,200), 2.426(34)(125), 1.8963(32)(225) and 1.8026(29)(0·1·10,233). The structure, refined toR1= 4.06% for 814Fo>4σFreflections, contains a neutral, wavy As2O3layer parallel to (001) consisting of As3+O3pyramids that share O atoms to form six-membered rings. Successive layers are flipped relative to one another and successive interlayer regions contain alternately either Na or Cl atoms. Torrecillasite is isostructural with synthetic orthorhombic NaAs4O6Br.

Mauriziodiniite, NH4(As2O3)2I, the ammonium and iodine analogue of lucabindiite from the Torrecillas mine, Iquique Province, Chile

“…Mauriziodiniite is a secondary alteration phase occurring on matrix consisting of native arsenic, arsenolite and pyrite in association with calcite, cuatrocapaite-(NH 4 ) (Kampf et al ., 2019 b ), lavendulan, magnesiokoritnigite (Kampf et al ., 2013) and torrecillasite (Kampf et al ., 2014). The secondary assemblages at the Torrecillas deposit are interpreted as principally having formed from the oxidation of native arsenic and other As-bearing primary phases, followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions ( cf .…”

“…5. Torrecillasite [Na(As 2 O 3 ) 2 Cl; Kampf et al ., 2014] also has a layer structure, with the sequence Cl–As 2 O 3 –Na–As 2 O 3 –Cl; however, the As 2 O 3 layer in torrecillasite is geometrically and topologically different from that in the other minerals.

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Juansilvaite, Na5Al3[AsO3(OH)]4[AsO2(OH)2]2(SO4)2·4H2O, a new arsenate-sulfate from the Torrecillas mine, Iquique Province, Chile

“…Over the last several years, our investigations of the minerals of this unusual deposit have yielded many new and potentially new mineral species. To date, the descriptions of six new minerals have been published: leverettite (Kampf et al, 2013a), magnesiokoritnigite (Kampf et al, 2013b), torrecillasite (Kampf et al, 2014a), canutite (Kampf et al, 2014b), chongite (Kampf et al, 2016a) and gajardoite (Kampf et al, 2016b). Herein, we describe the seventh new mineral from the Torrecillas mine, juansilvaite.…”

Magnesiocanutite, NaMnMg2[AsO4]2[AsO2(OH)2], a new protonated alluaudite-group mineral from the Torrecillas mine, Iquique Province, Chile

“…OVER the last several years, our investigations of the minerals of the Torrecillas mine, a small, longinactive arsenic mine in the northern Atacama Desert of Chile, have revealed a remarkable assemblage of rare secondary chlorides, arsenates and arsenites, many of which are new mineral species. To date, the descriptions of eight new minerals have been published: the chloride leverettite (Kampf et al, 2013a); the arsenates magnesiokoritnigite (Kampf et al, 2013b), canutite (Kampf et al, 2014a), chongite (Kampf et al, 2016a), currierite (Kampf et al, 2017a) and juansilvaite (Kampf et al, 2017b); and the arsenites torrecillasite (Kampf et al, 2014b) and gajardoite (Kampf et al, 2016b). Herein, we describe the ninth new mineral from the Torrecillas mine, the alluaudite-group arsenate magnesiocanutite.…”