Canutite, NaMn3[AsO4][AsO3(OH)]2, a new protonated alluaudite-group mineral from the Torrecillas mine, Iquique Province, Chile. (August 2014)

• Record Type: Journal Article
• Authors: Kampf, A. R.; Mills, S. J.; Hatert, F.; Nash, B. P.; Dini, M.; Molina Donoso, A. A.
• Is Part Of: Mineralogical magazine. Volume 78:Number 4(2014:Aug.)
• Page Start: 787
• Page End: 795
• Publication Date: 2014-08
• Subjects: canutite, -- new mineral, -- crystal structure, -- alluaudite group, -- Torrecillas mine, -- Chile; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/minmag.2014.078.4.02
• Languages: English
• ISSNs: 0026-461X

Abstract

Abstract: The new mineral canutite (IMA2013-070), NaMn3 [AsO4 ][AsO3 (OH)]2, was found at two different locations at the Torrecillas mine, Salar Grande, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, halite, lavendulan, magnesiokoritnigite, pyrite, quartz and scorodite. Canutite is reddish brown in colour. It forms as prisms elongated on [20 ] and exhibiting the forms {010}, {100}, {10 }, {201} and {102}, or as tablets flattened on {102} and exhibiting the forms {102} and {110}. Crystals are transparent with a vitreous lustre. The mineral has a pale tan streak, Mohs hardness of 2½, brittle tenacity, splintery fracture and two perfect cleavages, on {010} and {101}. The calculated density is 4.112 g cm −3 . Optically, canutite is biaxial (+) with α = 1.712(3), β = 1.725(3) and γ = 1.756(3) (measured in white light). The measured 2V is 65.6(4)°, the dispersion is r < v (slight), the optical orientation is Z =b ; X ^a = 18° in obtuse β and pleochroism is imperceptible. The mineral is slowly soluble in cold, dilute HCl. The empirical formula (for tabular crystals from near the mineshaft), determined from electron - microprobe analyses, is (Na1.05 Mn2.64 Mg0.34 Cu0.14 Co0.03 )∑4.20 As3 O12 H1.62 . Canutite is monoclinic, C 2/ c, a = 12.3282(4), b = 12.6039(5), c = 6.8814(5) Å, β = 113.480(8)°, V = 980.72(10) Å 3 and Z = 4. The eight strongest X-ray powder diffraction lines are [ d obs Å( I )( hkl )]: 6.33(34)(020), 4.12(26)( 21), 3.608(29)(310, 31), 3.296(57)( 12), 3.150(28)(002, 131), 2.819(42)(400, 041, 330), 2.740(100)(240, 02, 112) and 1.5364(31)(multiple). The structure, refined to R 1 = 2.33% for 1089 F o > 4σ F reflections, shows canutite to be isostructural with protonated members of the alluaudite group.