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 (Ca0.68Mn0.322+)Σ1.00(La0.49Ce0.39Pr0.02Nd0.02Sm0.01Eu0.01Gd0.01Th0.01Ca0.04)Σ1.00(Fe0.523+Fe0.042+Al0.34Ti0.104+)Σ1.00Al1.00(Mn0.532+Fe0.342+Mg0.13)Σ1.00(Si2.98Al0.02)Σ3.00O12.00(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.

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