Andrianovite, Na12(K,Sr,Ce)3Ca6Mn3Zr3Nb(Si25O73)(O, H2O,OH)5, a new potassium-rich mineral species of the eudialyte group from the Khibiny alkaline Pluton, Kola Peninsula, Russia

Abstract

This paper presents the description of a new eudialyte-group mineral, which was named andrianovite in honor of Valerii Ivanovich Andrianov (1938–1991), a famous Russian mathematician and crystallographer, who developed the AREN software package for structural study of minerals with variable composition. The new mineral has been found in pegmatite from the Koashva open pit, Khibiny Pluton, Kola Peninsula, as rims 0.1–1.0 mm wide surrounding the crystals of typical eudialyte. Aegirine, sodalite, microcline, natrolite, lomonosovite, lamprophyllite, mosandrite, and villiaumite are associated minerals. Andrianovite is light yellow, with vitreous luster and stepped fracture. It is transparent or turbid, with a white streak. The new mineral is brittle; the Mohs hardness is 5. The cleavage is imperfect parallel to (001). The measured density is 2.93(2) g/cm3 (volumetric method); the calculated density is 3.02 g/cm3. Andrianovite is optically uniaxial, negative; ω = 1.622(2), ɛ= 1.617(2). It is nonfluorescent and nonpleochroic. The new mineral slowly breaks down and gelates in 50% HCl and HNO3 at room temperature. It is trigonal, space group R3m. The unit cell dimensions are a = 14.281(4), c = 30.243(7) A, V = 5342(4) A3. The strongest reflections in the X-ray powder pattern [d, A (I, %)(hkl)] are as follows: 2.982(100)(315), 2.860(94)(404), 4.322(71)(205), 3.222(70)(208), 6.447(60)(104), 3.170(50)(217), 5.719(40)(202), 3.540(38)(027). The chemical composition (electron microprobe, H2O and CO2 determined by chemical analysis) is as follows, wt %: 11.61 Na2O, 2.05 K2O, 10.26 CaO, 3.11 SrO, 0.19 BaO, 3.97 MnO, 2.43 FeO, 0.81 La2O3, 1.73 Ce2O3, 0.52 Nd2O3, 0.28 Y2O3, 0.02 Al2O3, 47.06 SiO2, 0.12 TiO2, 11.32 ZrO2, 0.26 HfO2, 2.84 Nb2O5, 0.31 Cl, 0.57 CO2, 0.87 H2O, −O = 0.07 Cl2; total is 100.26. The empirical formula atcat = 53 (Z= 3) is Na12.09(K1.40Sr0.97REE0.60Ba0.04)Σ3.01(Ca5.90Y0.08).98(Mn1.81)Fe1.192+Σ2.90(Zr2.96Hf0.04)Σ3.0(Nb0.69Si0.27Ti0.05Al0.01)Σ1.02(Si25O73)[(O2.14(OH)0.52]Σ2.66[(H2O)1.30(CO3)0.42Cl0.28]Σ2.0. The simplified formula is Na12(K,Sr,Ce)3Ca6(Mn,Fe)3Zr3Nb(Si25O73)(O, H2O,OH)5. The infrared spectrum is given, and the crystal structure is described. The position of andrianovite in the crystallochemical taxonomy of the eudialyte group is shown, and its relationships with other eudialyte-group minerals (kentbrooksite, carbokentbrooksite, georgbarsanovite, etc.) are characterized. The type material of andrianovite has been deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.