Ferroinnelite, Ba₄Ti₂Na(NaFe²⁺)Ti(Si₂O₇)₂[(SO₄)(PO₄)]O₂[O(OH)], a new mineral of the lamprophyllite group (seidozerite supergroup) from the Kovdor alka

Abstract Ferroinnelite, Ba 4 Ti 2 Na(NaFe 2+ )Ti(Si 2 O 7 ) 2 [(SO 4 )(PO 4 )]O 2 [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 lustre and a white streak, D calc. is 4.088 g/cm 3 . Ferroinnelite is triclinic, space group P $\bar 1$ , 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) Å 3 . The chemical composition of ferroinnelite is SO 3 5.47, Nb 2 O 5 0.45, P 2 O 5 4.59, ZrO 2 0.13, TiO 2 16.91, SiO 2 17.55, Al 2 O 3 0.06, BaO 42.83, SrO 1.01, FeO 3.34, MnO 0.97, CaO 0.09, MgO 0.64, K 2 O 0.01, Na 2 O 4.47, H 2 O 1.11, F 0.15, O = F –0.06, total 99.72 wt.%, with H 2 O calculated from structure refinement. The empirical formula calculated on 26 (O + F) apfu is (Na 1.95 Fe 2+ 0.64 Mg 0.21 Mn 2+ 0.19 Ca 0.02 ) Σ3.01 (Ba 3.84 Sr 0.13 Na 0.03 ) Σ4.00 (Ti 2.91 Nb 0.05 Al 0.02 Zr 0.01 Mg 0.01 ) Σ3.00 Si 4.02 S 0.94 P 0.89 H 1.70 O 25.89 F 0.11 , Z = 1. The crystal structure was refined to an R 1 index of 7.45% from 4485 unique reflections ( F o > 4σ F ). The structure is a combination of a TS (Titanium Silicate) and an I (intermediate) blocks. The TS block consists of HOH sheets (H – heteropolyhedral and O – octahedral). The O sheet is composed of Ti-, Na- and (Na,Fe 2+ )-octahedra, the H sheet, of [5] Ti-polyhedra and Si 2 O 7 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 {Ti 2 Na(NaFe 2+ )Ti(Si 2 O 7 ) 2 O 2 [O(OH)]} 3– and {Ba 4 [(SO 4 )(PO 4 )]} 3+ . Ferroinnelite is a new member of the lamprophyllite group of the seidozerite supergroup. It is isostructural with innelite-1 A , Ba 4 Ti 2 Na(NaMn 2+ )Ti(Si 2 O 7 ) 2 [(SO 4 )(PO 4 )]O 2 [O(OH)]. Ferroinnelite and innelite are related by the following cation substitution at the M O 3 site in the O sheet: Fe 2+ fer ↔ Mn 2+ inn . IR and Raman spectroscopies confirm presence of OH and H 2 O groups in ferroinnelite and innelite.