GLADIUSITE, Fe3+2(Fe2+,Mg)4(PO4)(OH)11(H2O), A NEW HYDROTHERMAL MINERAL SPECIES FROM THE PHOSCORITE CARBONATITE UNIT, KOVDOR COMPLEX, KOLA PENINSULA, RUSSIA

Abstract

Gladiusite, ideally Fe 3+ 2 (Fe 2+ ,Mg) 4 (PO 4 )(OH) 11 (H 2 O), monoclinic, a 16.959(2), b 11.650(3), c 6.266(6) A, β 90.00(5)°, V 1238(1) A 3 , space group P 2 1 / n , Z = 4, is a new mineral species from hydrothermal assemblages associated with the phoscorite–carbonatite unit of the Kovdor alkaline-ultramafic complex, Kola Peninsula, Russia. It occurs in vugs within veins of mineralized dolomite carbonatite. Associated minerals are dolomite, pyrochlore, several generations of magnetite, pyrite, rutile, a ternovite-like phase, catapleiite, bobierrite, rimkorolgite, juonniite, strontiowhitlockite, collinsite (including a Sr-rich variety) and chlorite. Gladiusite occurs as acicular aggregates and as free-standing radial clusters ( 3 , respectively. Gladiusite is biaxial negative and strongly pleochroic, α 1.722(2), β 1.730(2), γ 1.737(2), 2 V calc. = 78.3°. The strongest reflections in the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 9.61(53)(110), 6.87(77)(210), 5.83(89)(020), 4.805(100)(220), 3.787(62)(130), 3.533(84)(230), and 2.868(66)(140). Electron-microprobe analysis and Mossbauer spectroscopy gave (wt.%) FeO 25.00, Fe 2 O 3 29.90, MgO 11.16, MnO 0.78, P 2 O 5 12.46, TiO 2 0.04, H 2 O(calc.) = 20.18, sum = 99.51 wt.%; the H 2 O content, obtained by the Penfield method, is 19.7 wt.%. The unit formula is Fe 3+ 2.00 [Fe 2+ 2.02 Mg 1.61 Fe 3+ 0.17 Mn 2+ 0.06 ] ∑3.86 (P 1.02 O 4 )(OH) 11 (H 2 O) on the basis of 16 O atoms. The simplified formula is Fe 3+ 2 (Fe 2+ ,Mg) 4 (PO 4 )(OH) 11 (H 2 O). Crystal-structure study showed gladiusite to be extensively twinned on [001]. Gladiusite is considered to be a product of hydrothermal alteration of pyrrhotite and fluorapatite, the primary Fe and P minerals in the dolomite carbonatite. The mineral is named in accordance with the morphology of the crystals, which resemble double-edge swords ( gladius , in Latin) in SEM images.