Original paper

Lileyite, Ba2(Na,Fe,Ca)3MgTi2(Si2O7)2O2F2, a new lamprophyllite-group mineral from the Eifel volcanic area, Germany

Chukanov, Nikita V.; Pekov, Igor V.; Rastsvetaeva, Ramiza K.; Aksenov, Sergey M.; Zadov, Aleksandr E.; Van, Konstantin V.; Blass, Günter; Schüller, Willi; Ternes, Bernd

Abstract

The new Mg- and F-dominant lamprophyllite-group mineral lileyite (IMA 2011-021) was found at the Löhley quarry, Üdersdorf, near Daun, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany, and named for the old name of the type locality, Liley. Associated minerals are nepheline, leucite, augite, magnetite, fluorapatite, perovskite, götzenite. Lileyite is brown, translucent; streak is white. It forms platy crystals up to 0.1 × 0.3 × 0.5 mm in size and their clusters up to 1 mm across on the walls of cavities in an alkaline basalt. Lileyite is brittle, with Mohs hardness of 3-4 and perfect cleavage on (001). Dcalc is 3.776 g/cm3. The new mineral is biaxial (+), α = 1.718(5), β = 1.735(5), γ = 1.755(5), 2V (meas.) = 75(15)°, 2V (calc.) = 86°. The IR spectrum is given. The chemical composition is (EDS-mode electron microprobe, mean of 5 analyses, wt%): SiO2 28.05, BaO 26.39, TiO2 18.53, Na2O 6.75, MgO 4.58, FeO 4.48, CaO 2.30, SrO 2.23, MnO 1.44, K2O 1.41, Nb2O5 0.95, F 3.88, O=F2 -1.63; total 99.36. The empirical formula based on 18 anions is: Ba1.50Sr0.19K0.26Na1.89Ca0.36Mn0.18Mg0.99Fe0.54Ti2.01Nb0.06Si4.06O16.23F1.77. The simplified formula is: Ba2(Na,Fe,Ca)3MgTi2(Si2O7)2O2F2. The crystal structure was solved using single-crystal X-ray diffraction data (R = 0.024). Lileyite is monoclinic, space group C2/m, a = 19.905(1), b = 7.098(1), c = 5.405(1) Å, β = 96.349(5), V = 758.93(6) Å3, Z = 2. The strongest lines of the powder diffraction pattern [d, Å (I, %) (hkl)] are: 3.749 (45) (31-1), 3.464 (76) (510, 311, 401), 3.045 (37) (51-1), 2.792 (100) (221, 511), 2.672 (54) (002, 601, 20-2), 2.624 (43) (710, 42-1). Type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, registration number 4106/1.

Keywords

lileyitenew minerallamprophyllite groupheterophyllosilicatescrystal structureeifelgermany