New data on ferriakasakaite-(La) and related minerals extending the compositional field of the epidote supergroup
Chukanov, Nikita V.; Zubkova, Natalia V.; Schäfer, Christof; Varlamov, Dmitry A.; Ermolaeva, vera N.; polekhovsky, Yury S.; Jančev, Simeon; Pekov, Igor V.; Pushcharovsky, Dmitry Yu.
European Journal of Mineralogy Volume 30 Number 2 (2018), p. 323 - 332
34 references
published: Aug 20, 2018
published online: May 24, 2018
manuscript accepted: Dec 5, 2017
final revised version received: Oct 10, 2017
manuscript received: Aug 10, 2017
Abstract
Detailed studies of ferriakasakaite-(La) including determination of chemical composition and crystal structure, infrared spectroscopy, optical characteristics in reflected light and micro-indentation hardness have been carried out on a non-metamict sample from young nosean-bearing sanidinite from the Laach Lake volcanic complex, Eifel, Germany. The chemical composition is (electron microprobe, Fe2+: Fe3+ determined from structural data, wt.%): CaO 6.74, La2O3 13.35, Ce2O3 10.58, Pr2O3 0.42, Nd2O3 0.49, Sm2O3, 0.34, Eu2O3 0.18, Gd2O3 0.20, ThO2 0.43, UO2 0.10, MgO 0.89, MnO 9.98, Al2O3 11.47, Fe2O3 7.39, FeO 4.04, TiO2 1.32, SiO2 29.80, H2O (calc.) 1.49, total 99.22. The empirical formula is ( Ca 0 .68 M n 0 .32 2+ ) Σ 1 .00 ( La 0 .49 Ce 0 .39 Pr 0 .02 Nd 0 .02 Sm 0 .01 Eu 0 .01 Gd 0 .01 Th 0 .01 Ca 0 .04 ) Σ 1 .00 ( F e 0 .52 3+ F e 0 .04 2+ Al 0 .34 T i 0 .10 4+ ) Σ 1 .00 Al 1 .00 ( M n 0 .53 2+ F e 0 .34 2+ Mg 0 .13 ) Σ 1 .00 ( Si 2 .98 Al 0 .02 ) Σ 3 .00 O 12 .00 ( OH ) . The crystal structure was solved by direct methods and refined to R = 0.018 based on 1259 unique reflections with I > 2σ(I). The H atom was located. The mineral is monoclinic, space group P21/m, a = 8.9054(1), b = 5.7545(1), c = 10.1037(2) Å, β = 114.103(2)°, V = 472.63(1) Å3. The IR spectrum confirms the presence of OH groups. Reflectance spectra of ferriakasakaite-(La) obtained in the visible range show reflectance minima at the wavelength of ∼590 nm. Various epidote-supergroup minerals including ferriakasakaite-(La), allanite-(Ce), Al-dominant (at the M1 site) analogue of ferriakasakaite-(Ce), piemontite, piemontite-(Pb), as well as Pb-, Zn- and Cu-bearing varieties of Fe3+-dominant (at the M1 site) analogues of piemontite and piemontite-(Pb), have been discovered in sulfide-free metasomatic rocks containing oxide/oxysalt compounds of chalcophile elements (Zn, Cu, Sb, and Pb), within the Pelagonian massif, Republic of Macedonia. Crystal chemical regularities of these minerals are discussed.
Keywords
epidote supergroup • allanite group • ferriakasakaite-(La) • crystal structure • Laach Lake volcanic complex • Germany • Nežilovo • Pelagonian massif • Macedonia
