Publication details

The mineralogy of the historical Mochalin Log REE deposit, South Urals, Russia. Part V. Zilbermintsite-(La), (CaLa5)(Fe3+Al3Fe2+)[Si2O7][SiO4]5O(OH)3, a new mineral with ET2 type structure and a definition of the radekškodaite group

Authors	KASATKIN Anatoly V. ZUBKOVA Natalia V. ŠKODA Radek PEKOV Igor V. AGAKHANOV Atali A. GURZHIY Vladislav V. KSENOFONTOV Dmitriy A. BELAKOVSKIY Dmitriy I. KUZNETSOV Aleksey M.
Year of publication	2024
Type	Article in Periodical
Magazine / Source	Mineralogical Magazine
MU Faculty or unit	Faculty of Science
Citation
web	https://www.cambridge.org/core/journals/mineralogical-magazine/article/mineralogy-of-the-historical-mochalin-log-ree-deposit-south-urals-russia-part-v-zilbermintsitela-cala5fe3al3fe2si2o7sio45ooh3-a-new-mineral-with-et2-type-structure-and-a-definition-of
Doi	http://dx.doi.org/10.1180/mgm.2024.17
Keywords	zilbermintsite-(La); new mineral; crystal structure; ET2 type; radek & scaron;kodaite group; Mochalin Log; South Urals
Description	The new mineral zilbermintsite-(La), ideally (CaLa5)(Fe3+Al3Fe2+)[Si2O7][SiO4](5)O(OH)(3), was found in a single polymineralic nodule from the Mochalin Log REE deposit, Chelyabinsk Oblast, South Urals, Russia. Zilbermintsite-(La) forms anhedral grains up to 0.65 x 0.20 mm at the contact of ferriperb & oslash;eite-(La), t & ouml;rnebohmite-(La) and ferriallanite-(Ce). Other associated minerals include bastn & auml;site-(La), biraite-(La), ferriallanite-(La), ferriperb & oslash;eite-(Ce), fluorbritholite-(Ce), monazite-(La), perb & oslash;eite-(La), percleveite-(Ce), percleveite-(La), perrierite-(Ce), perrierite-(La), thorianite, thorite and quartz. The new mineral is light brown, translucent in thin fragments with a vitreous lustre. It is brittle, with good {100} cleavage. Mohs hardness is ca. 6. D-calc = 4.684 g cm(-3). Optically, zilbermintsite-(La) is biaxial (+), alpha = 1.805(7), beta = 1.812(7) and gamma = 1.867(8) (589 nm); 2V(meas) = 40(15)degrees and 2V(calc) = 40 degrees. The empirical formula based on O-28(OH,F)(3) apfu is (Ca0.94La2.56Ce2.18Nd0.20Pr0.10Th0.02)(Sigma 6.00)(Al2.96Fe0.903+Fe0.642+Mg0.34Mn0.13Ti0.03)(Sigma 5.00)Si7.00O28[(OH)(2.42)F-0.58]. Zilbermintsite-(La) is monoclinic, P2(1)/m; the unit-cell parameters are: a = 8.9605(5), b = 5.7295(2), c = 25.1033(13) & Aring;, beta = 116.616(7), V = 1152.21(12) & Aring;(3) and Z = 2. The crystal structure of zilbermintsite-(La) is solved from the single-crystal X-ray diffraction data [R = 0.0757 for 2857 unique reflections with I > 2 sigma(I)]. The new mineral is isotypic to radek & scaron;kodaite-(La) and radek & scaron;kodaite-(Ce) and together with them forms the newly defined radek & scaron;kodaite group. All members of this group possess the ET2 type structure where one epidote-type module (E) regularly alternates with two t & ouml;rnebohmite-type modules (T). The new mineral honours Professor Veniamin A. Zilbermints (1887-1939) who was a pioneer of the study of the Mochalin Log deposit. The Levinson suffix-modifier -(La) indicates the predominance of La among rare-earth elements in the mineral.