Original paper

Stronadelphite, Sr5(PO4)3F, a new apatite-group mineral

Pekov, Igor V.; Britvin, Sergey N.; Zubkova, Natalia V.; Pushcharovsky, Dmitry Yu.; Pasero, Marco; Merlino, Stefano

Abstract

The new apatite-group mineral stronadelphite was found in the Belovitovoye peralkaline pegmatite at the Kirovskii apatite mine, Mt. Kukisvumchorr, Khibiny alkaline complex, Kola peninsula, Russia. Associated minerals are natrolite, microcline, aegirine, pectolite, lamprophyllite, belovite-(Ce), belovite-(La), gaidonnayite, nenadkevichite, komarovite, manganokukisvumite, epididymite, sphalerite, neotocite, etc. Stronadelphite forms hexagonal, prismatic to acicular crystals up to 0.1 × 0.1 × 2 mm, combined in sheaf-like clusters up to 1 × 2 mm embedded in natrolite. The mineral is transparent, colourless with a pale greenish tint. Stronadelphite is brittle, with Mohs hardness 5, no cleavage observed. Dcalc is 3.915 g/cm3. Optically, the new mineral is uniaxial (-), ω 1.630(1), ε 1.623(1). Average values for six point microprobe analyses (wt%) are: Na2O 0.10, CaO 2.49, SrO 62.72, BaO 2.40, La2O30.34, Ce2O3 0.22, ThO2 0.28, P2O5 29.02, F 1.45, H2O(calc.) 0.54, -O=F2 -0.61; total 98.95. The empirical formula based on 13 anions [O12(F,OH)] is: (Sr4.46Ca0.33Ba0.12Na0.02La0.02Ce0.01Th0.01)Σ=4.97P3.01O12[F0.56(OH)0.44]Σ=1. The idealized formula is Sr5(PO4)3F. Stronadelphite is hexagonal, space group P63/m; a = 9.845(7), c = 7.383(4) Å, V = 619.7(7) Å3, Z = 2. Its crystal structure has been refined to R = 0.0305 using single-crystal X-ray diffraction data. Stronadelphite is isostructural with fluorapatite. The strongest lines of the powder diffraction pattern [d in Å (I) (hkl)] are: 3.71 (30) (002), 3.21 (40) (120, 210), 2.940 (100) (211, 121, 112), 2.823 (35) (300, 202), 2.009 (50) (222, 312, 132), 1.955 (45) (213, 123), 1.500 (30) (151, 511, 332). The mineral is named after the chemical element strontium and αδελϕóσ, Greek for “brother”, as the full strontium analogue of fluorapatite, the most widespread member of the apatite supergroup. Both the mineral and its name have been approved by the IMA CNMNC. The type specimen is deposited in Fersman Mineralogical Museum, Moscow, with the registration number 3693/1.

Keywords

stronadelphitenew mineralapatite groupcrystal structureperalkaline pegmatitekhibiny alkaline complexkola peninsulastrontium flurophosphate