Abstract
A new mineral, ferroindialite, a Fe2+-dominant analog of indialite, has been found in a pyrometamorphosed xenolith of pelitic rock hosted in alkaline basalts. Associated minerals are phlogopite, sanidine, sillimanite, pyroxenes of the enstatite-ferrosilite series, wagnerite, fluorapatite, tridymite, zircon and almandine. Ferroindialite forms brown-purple to gray with a violet-blue tint short prismatic or thick tabular hexagonal crystals up to 1.5 mm in size. The new mineral is brittle, with a Mohs’ hardness of 7. Cleavage is not observed. D meas = 2.66(1), D calc = 2.667 g/cm3. IR spectrum shows neither H2O nor OH groups. Ferroindialite is anomalously biaxial (−), α = 1.539(2), β = 1.552(2), γ = 1.554(2), 2V meas = 30(10)°. The mineral is weakly pleochroic, ranging from colorless on X to pale violet on Z. Dispersion is weak, r < v. The chemical composition (electron microprobe, mean of five point analyses, wt %) is as follows: 0.14 Na2O, 0.46 K2O, 4.95 MgO, 1.13 MnO, 12.66 FeO, 2.64 Fe2O3, 30.45 Al2O3, 47.22 SiO2, total is 99.65. The distribution of total iron content between Fe2+ and Fe3+ was carried out according to structural data. The empirical formula of ferroindialite is: (K0.06Na0.03)(Fe 2+1.12 Mg0.78Mn0.10)Σ2.00(Al3.79Fe 3+0.21 )Σ4.00Si4.98O18. The simplified formula is: (Fe2+,Mg)2Al4Si5O18. The crystal structure has been refined on a single crystal, R = 0.049. Ferroindialite is hexagonal, space group P6/mcc; a = 9.8759(3), c = 9.3102(3) Å, V = 786.40(3) Å3, Z = 2. The strongest lines in the X-ray powder diffraction pattern [d, Å (I, %) (hkl)] are: 8.59 (100) (100), 4.094 (27) (102), 3.390 (35) (112), 3.147 (19) (202), 3.055 (31) (211), 2.657 (12) (212), 1.695 (9) (224). The type specimen of ferroindialite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 4400/1.
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Original Russian Text © N.V. Chukanov, S.M. Aksenov, I.V. Pekov, B. Ternes, W. Schüller, D.I. Belakovskiy, K.V. Van, G. Blass, 2014, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2014, No. 1, pp. 46–56.
A new mineral species, ferroindialite, and its name considered by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society and approved by the Commission on New Minerals, Nomenclature, and Classification of Minerals of the International Mineralogical Association, May 1, 2013, IMA no. 2013-016.
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Chukanov, N.V., Aksenov, S.M., Pekov, I.V. et al. Ferroindialite (Fe2+,Mg)2Al4Si5O18, a new beryl-group mineral from the Eifel volcanic region, Germany. Geol. Ore Deposits 56, 637–643 (2014). https://doi.org/10.1134/S1075701514080029
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DOI: https://doi.org/10.1134/S1075701514080029