Currierite, Na 4 Ca 3 MgAl 4 (AsO 3 OH) 12 ·9H 2 O, a new acid arsenate with ferrinatrite-like heteropolyhedral chains from the Torrecillas mine, Iquique Province, Chile

The new mineral currierite (IMA2016-030), Na 4 Ca 3 MgAl 4 (AsO 3 OH) 12 ·9H 2 O, was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, canutite, chudobaite, halite, lavendulan, magnesiokoritnigite, quartz, scorodite and torrecillasite. Currierite occurs as hexagonal prisms, needles and hair-like fibres up to ∼200 μm long, in sprays. The crystal forms are ﹛100﹜ and ﹛001﹜. Crystals are transparent, with vitreous to silky lustre and white streak. The Mohs hardness is ∼2, tenacity is brittle, but elastic in very thin fibres, and the fracture is irregular. Crystals exhibit at least one good cleavage parallel [001]. The measured density is 3.08(2) g cm -3 and the calculated density is 3.005 g cm -3 . Optically, currierite is uniaxial (–) with ω= 1.614(1) and ε= 1.613(1) (measured in white light). The mineral is slowly soluble in dilute HCl at room temperature. The empirical formula, determined from electron-microprobe analyses, is (Na 3.95 A1 2.96 Ca 2.74 Mg 1.28 Fe 0.63 3+ Cu 0.13 K 0.08 Co 0.03 Σ11.80 (AS 11.68 5+ Sb 0.32 5+ Σ12(O 56.96 Cl 0.04 )Σ57H 30.81 . Currierite is hexagonal, P622 , with a = 12.2057(9), c = 9.2052(7) Å, V = 1187.7(2) Å 3 and Z = 1. The eight strongest powder X-ray diffraction lines are [ d obs Å (I)(hkl) ]: 10.63(100)(100), 6.12(20)(110), 5.30(15)(200), 4.61(24)(002), 4.002(35)(210), 3.474(29)(202), 3.021(96)(212) and 1.5227(29)(440,334,612). The structure of currierite ( R 1 = 2.27% for 658 F o > 4σ F reflections) is based upon a heteropolyhedral chain along c in which AlO 6 octahedra are triple-linked by sharing corners with AsO 3 OH tetrahedra. Chains are linked to one another by bonds to 8(4 + 4)-coordinated Na and 8-coordinated Ca forming a three-dimensional framework with large cavities that contain rotationally disordered Mg(H 2 O) 6 octahedra. The chain in the structure of currierite is identical to that in kaatialaite and a geometrical isomer of that in ferrinatrite. The mineral is named in honour of Mr. Rock Henry Currier (1940–2015), American mineral dealer, collector, author and lecturer.