HENRYMEYERITE, A NEW HOLLANDITE-TYPE Ba-Fe TITANATE FROM THE KOVDOR COMPLEX, RUSSIA

Abstract

A new hollandite-type titanate, henrymeyerite, occurs in a vein of tetra-ferriphlogopite ‐ calcite ‐ dolomite carbonatite of the Kovdor alkaline ultramafic complex, Kola Peninsula, in Russia. The mineral was found in a single mineralized vug as acicular crystals less than 0.2 mm in length. The crystals represent a combination of two tetragonal prisms and a bipyramid. Henrymeyeri te is opaque, black, and has an adamantine luster. In reflected light, the mineral is greyish brown and has a strong bireflectance . Reflectance values R« and Rv are given for l over the interval 420‐720 nm. Henrymeyerite is associated with dolomite, fluorapatite, tetra-ferriphlogopite, rimkorolgite, catapleiite, collinsite, and pyrite. The composition of henrymeyerite, as de termined by electron microprobe, is (wt.%): BaO 18.25, TiO 2 67.78, FeO 9.20, Nb2O5 1.00, Ce2O3 0.56, La2O3 0.50, Na2O 0.40, SiO2 0.37, K2O 0.05, CaO 0.02, sum 98.13. Stoichiometrically, this composition closely corresponds to the Ba‐Fe end-member of the cryptomelane group, BaFe 2+ Ti7O16. Henrymeyerite is tetragonal, space group I4/m, Z = 1, a 10.219(3), c 2.963(1) A, V 309.4(3) A 3 . The crystal structure of the mineral was refined to R1 = 0.027 for 173 unique reflections with | Fo | ♢ 4sF using single-crystal X-ray-diffraction data. The structure of henrymeyerite corresponds to the undistorted hollandite archetype; no indication of splitting of the Ba site along [001] was observed. The available single-crystal data also indicate the absence of longrange order of the Ba 2+ cations within the structural tunnels. The mineral is named for Prof. Henry O.A. Meyer (1937‐1995) in honor of his contributions to the petrology and mineralogy of mantle-derived xenoliths and kimberlitic rocks.