ALBERT

Description: The new mineral canutite (IMA2013-070), NaMn 3 [AsO 4 ][AsO 3 (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 [201I] and exhibiting the forms {010}, {100}, {102}, {201} and {102I}, 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 21/2, 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 = 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 mine shaft), determined from electron-microprobe analyses, is (Na 1.05 Mn 2.64 Mg 0.34 Cu 0.14 Co 0.03 ) 4.20 As 3 O 12 H 1.62 . 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)(2I21), 3.608(29)(310,1I31), 3.296(57)(1I12), 3.150(28)(002,131), 2.819(42)(400,041,330), 2.740(100)(240,4I02,112) and 1.5364(31)(multiple). The structure, refined to R 1 = 2.33% for 1089 F o 〉 4 F reflections, shows canutite to be isostructural with protonated members of the alluaudite group.