ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉Laverovite (IMA 2017-009b), ideally K〈sub〉2〈/sub〉NaMn〈sub〉7〈/sub〉Zr〈sub〉2〈/sub〉(Si〈sub〉4〈/sub〉O〈sub〉12〈/sub〉)〈sub〉2〈/sub〉O〈sub〉2〈/sub〉(OH)〈sub〉4〈/sub〉F, is a kupletskite-group (astrophyllite-supergroup) mineral from Mont Saint-Hilaire, Québec, Canada. Associated minerals are zircophyllite, kupletskite, astrophyllite, aegirine, analcime, orthoclase, and albite. Laverovite is brown, transparent in thin grains, and has a vitreous luster. Mohs hardness is 3, 〈span〉D〈/span〉〈sub〉calc.〈/sub〉 = 3.367 g/cm〈sup〉3〈/sup〉. Laverovite is biaxial (–) with refractive indices (λ = 589 nm) α = 1.670(2), β = 1.710(5), γ = 1.740(5); 2〈span〉V〈/span〉〈sub〉meas.〈/sub〉 = 82(2)°, 2〈span〉V〈/span〉〈sub〉calc.〈/sub〉 = 80°, strong dispersion: 〈span〉r〈/span〉 〉 〈span〉v〈/span〉. Cleavage is perfect parallel to {001}. Chemical analysis by electron microprobe gave Nb〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 0.56, ZrO〈sub〉2〈/sub〉 9.78, TiO〈sub〉2〈/sub〉 4.69, SiO〈sub〉2〈/sub〉 33.52, Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 0.94, SrO 0.13, ZnO 0.07, FeO 13.94, MnO 20.51, CaO 0.48, MgO 0.76, Cs〈sub〉2〈/sub〉O 0.05, K〈sub〉2〈/sub〉O 6.00, Na〈sub〉2〈/sub〉O 2.28, F 1.80, H〈sub〉2〈/sub〉O〈sub〉calc.〈/sub〉 2.57, sum 97.32 wt.%; H〈sub〉2〈/sub〉O was calculated from crystal-structure analysis. The empirical formula based on 31.15 (O + F) 〈span〉apfu〈/span〉 with [OH + F = 5 〈span〉pfu〈/span〉 and H〈sub〉2〈/sub〉O = 0.15 〈span〉pfu〈/span〉] is (K〈sub〉1.78〈/sub〉Sr〈sub〉0.02〈/sub〉Cs〈sub〉0.01〈/sub〉□〈sub〉0.19〈/sub〉)〈sub〉Σ2〈/sub〉(□〈sub〉1.85〈/sub〉Na〈sub〉0.15〈/sub〉)〈sub〉Σ2〈/sub〉(Na〈sub〉0.88〈/sub〉Ca〈sub〉0.12〈/sub〉)〈sub〉Σ1〈/sub〉(Mn〈sub〉4.03〈/sub〉Fe〈sup〉2+〈/sup〉〈sub〉2.71〈/sub〉Mg〈sub〉0.25〈/sub〉Zn〈sub〉0.01〈/sub〉)〈sub〉Σ7〈/sub〉(Zr〈sub〉1.11〈/sub〉Ti〈sub〉0.82〈/sub〉Nb〈sub〉0.06〈/sub〉Mg〈sub〉0.01〈/sub〉)〈sub〉Σ2〈/sub〉[(Si〈sub〉7.78〈/sub〉Al〈sub〉0.26〈/sub〉)〈sub〉Σ8.04〈/sub〉O〈sub〉24〈/sub〉]O〈sub〉2〈/sub〉[(OH)〈sub〉3.68〈/sub〉F〈sub〉0.32〈/sub〉]〈sub〉Σ4〈/sub〉F[□〈sub〉1.85〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉0.15〈/sub〉]〈sub〉Σ2〈/sub〉, 〈span〉Z〈/span〉 = 1. The simplified formula is K〈sub〉2〈/sub〉Na(Mn,Fe〈sup〉2+〈/sup〉)〈sub〉7〈/sub〉(Zr,Ti)〈sub〉2〈/sub〉(Si〈sub〉4〈/sub〉O〈sub〉12〈/sub〉)〈sub〉2〈/sub〉O〈sub〉2〈/sub〉 (OH)〈sub〉4〈/sub〉F. Laverovite is triclinic, space group 〈span〉P〈/span〉, 〈span〉a〈/span〉 5.4329(1), 〈span〉b〈/span〉 11.9232(3), 〈span〉c〈/span〉 11.7491(3) Å, α 112.905(2), β 94.696(1), γ 103.178(1)°, 〈span〉V〈/span〉 670.14(5) Å〈sup〉3〈/sup〉. The six strongest lines in the X-ray powder diffraction data [〈span〉d〈/span〉 (Å)(I)(〈span〉hkl〈/span〉)] are: 3.452(92)(003,111); 2.788(97); 2.680(68); 2.589(100); 2.504(44), and 1.590(50). The crystal structure has been refined to 〈span〉R〈/span〉〈sub〉1〈/sub〉 = 3.26% for 3757 observed (〈span〉F〈/span〉〈sub〉o〈/sub〉 〉 4σ〈span〉F〈/span〉) reflections. In the crystal structure of laverovite, there are four 〈sup〉[4]〈/sup〉〈span〉T〈/span〉 sites, with 〈T–O〉 = 1.621 Å, occupied mainly by Si, with minor Al. TO〈sub〉4〈/sub〉 tetrahedra constitute the T〈sub〉4〈/sub〉O〈sub〉12〈/sub〉 astrophyllite ribbon. The Zr-dominant 〈sup〉[6]〈/sup〉〈span〉D〈/span〉 site is occupied mainly by Zr and Ti and minor Nb and Mg, with 〈D–φ〉 = 2.002 Å (φ = O, F). The T〈sub〉4〈/sub〉O〈sub〉12〈/sub〉 astrophyllite ribbons and D octahedra constitute the H (Heteropolyhedral) sheet. In the O (Octahedral) sheet, there are four Mn〈sup〉2+〈/sup〉-dominant 〈sup〉[6]〈/sup〉〈span〉M〈/span〉(1–4) sites, with 〈M(1–4)–φ〉 = 2.187, 2.174, 2.161, and 2.146 Å (φ = O, OH). Two H sheets and the central O sheet form the HOH block, and adjacent HOH blocks link 〈span〉via〈/span〉 a common X〈span〉P〈/span〉〈sub〉D〈/sub〉 anion of two D octahedra. In the 〈strong〉I〈/strong〉 (Intermediate) block between adjacent HOH blocks, there are two interstitial cation sites, 〈span〉A〈/span〉 and 〈span〉B〈/span〉, and a 〈span〉W〈/span〉〈sub〉A〈/sub〉 site, partly occupied by H〈sub〉2〈/sub〉O. The 〈span〉A〈/span〉 site splits into two partly occupied sites, 〈sup〉[13]〈/sup〉〈span〉A〈/span〉(1) and 〈sup〉[6]〈/sup〉〈span〉A〈/span〉(2), with A(1)–A(2) = 1.108 Å. The 〈sup〉[13]〈/sup〉〈span〉A〈/span〉(1) site is occupied at 90.5%: mainly by K, with minor Sr and Cs, 〈A(1)–φ〉 = 3.326 Å; the 〈sup〉[6]〈/sup〉〈span〉A〈/span〉(2) site is occupied at 7.5% by Na: [□〈sub〉1.85〈/sub〉Na〈sub〉0.15〈/sub〉], 〈A(2)–φ〉 = 2.29 Å (φ = O, F, H〈sub〉2〈/sub〉O). The aggregate content of the 〈span〉A〈/span〉 site is (K〈sub〉1.78〈/sub〉Sr〈sub〉0.02〈/sub〉Cs〈sub〉0.01〈/sub〉Na〈sub〉0.15〈/sub〉□〈sub〉0.04〈/sub〉)〈sub〉Σ2〈/sub〉, ideally K〈sub〉2〈/sub〉〈span〉apfu〈/span〉. The 〈sup〉[10]〈/sup〉〈span〉B〈/span〉 site is occupied by (Na〈sub〉0.88〈/sub〉Ca〈sub〉0.12〈/sub〉), 〈〈span〉B〈/span〉–φ〉 = 2.646 Å. The 〈span〉W〈/span〉〈sub〉A〈/sub〉 site is occupied at 7.5% by H〈sub〉2〈/sub〉O: [□〈sub〉1.85〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉0.15〈/sub〉] 〈span〉pfu〈/span〉. The presence of OH and H〈sub〉2〈/sub〉O groups in the laverovite structure was confirmed by infrared spectroscopy. The mineral is named “laverovite” after Professor Nikolay Pavlovich Laverov (1930–2016), Academician of the Russian Academy of Sciences, a prominent Russian ore geologist and an expert in uranium ore deposits and radiogenic waste disposal. Laverovite is a Mn-analogue of zircophyllite, K〈sub〉2〈/sub〉NaFe〈sup〉2+〈/sup〉〈sub〉7〈/sub〉Zr〈sub〉2〈/sub〉(Si〈sub〉4〈/sub〉O〈sub〉12〈/sub〉)〈sub〉2〈/sub〉O〈sub〉2〈/sub〉(OH)〈sub〉4〈/sub〉F. 〈/span〉