Ferroinnelite, Ba4Ti2Na(NaFe2+)Ti(Si2O7)2[(SO4)(PO4)]O2[O(OH)], a new mineral of the lamprophyllite group (seidozerite supergroup) from the Kovdor alkaline massif, Kola Peninsula, Russia: description and crystal structure and new data for innelite, Ba4Ti2Na(NaMn2+)Ti(Si2O7)2[(SO4)(PO4)]O2[O(OH)]

Ferroinnelite, Ba4Ti2Na(NaFe2+)Ti(Si2O7)2[(SO4)(PO4)]O2[O(OH)] is a new mineral from the Phlogopite deposit, Kovdor alkaline massif, Kola Peninsula, Russia. In an agpaitic pegmatite, ferroinnelite occurs as transparent elongated platy to tabular crystals up to 0.15 mm long. Associated minerals are cancrinite, orthoclase, aegirine-augite, magnesio-arfvedsonite, golyshevite and fluorapatite. The mineral is yellow to yellow brown with a vitreous luster and a white streak, Dcalc. is 4.088 g/cm3. Ferroinnelite is triclinic, space group P1, a 5.3994(8), b 7.09239(13), c 14.7345(4) Å, α 98.4086(19), β 94.3275(18), γ 90.0133(13)°, V 556.56(8) Å3. The chemical composition of ferroinnelite is SO3 5.47, Nb2O5 0.45, P2O5 4.59, ZrO2 0.13, TiO2 16.91, SiO2 17.55, Al2O3 0.06, BaO 42.83, SrO 1.01, FeO 3.34, MnO 0.97, CaO 0.09, MgO 0.64, K2O 0.01, Na2O 4.47, H2O 1.11, F 0.15, O = F –0.06, total 99.72 wt.%, with H2O calculated from structure refinement. The empirical formula calculated on 26 (O + F) apfu is (Na1.95Fe2+0.64Mg0.21Mn2+0.19Ca0.02)Σ3.01(Ba3.84Sr0.13Na0.03)Σ4.00(Ti2.91Nb0.05Al0.02Zr0.01Mg0.01)Σ3.00 Si4.02S0.94P0.89H1.70O25.89F0.11, Z = 1. The crystal structure was refined to an R1 index of 7.45% from 4485 unique reflections (Fo > 4σF). The structure is a combination of a TS (titanium silicate) and an I (intermediate) blocks. The TS block consists of HOH sheets (H - heteropolyhedral, O - octahedral). The O sheet is composed of Ti-, Na- and (Na,Fe2+)octahedra, the H sheet, of [5]Ti-polyhedra and Si2O7 groups. The I block contains T sites, statistically occupied by S and P, and Ba atoms. Ideal compositions of the TS and I blocks are {Ti2Na(NaFe2+)Ti(Si2O7)2O2[O(OH)]}3– and {Ba4[(SO4)(PO4)]}3+. Ferroinnelite is a new member of the lamprophyllite group of the seidozerite supergroup. It is isostructural with innelite-1A, Ba4Ti2Na(NaMn2+)Ti(Si2O7)2[(SO4)(PO4)]O2[O(OH)]. Ferroinnelite and innelite are related by the following cation substitution at the MO3 site in the O sheet: Fe2+fer ↔ Mn2+inn. IR and Raman spectroscopies confirm presence of OH and H2O groups in ferroinnelite and innelite.