Publication details

The mineralogy of the historical Mochalin Log REE deposit, South Urals, Russia. Part IV. Alexkuznetsovite-(La), La2Mn(CO3)(Si2O7), alexkuznetsovite-(Ce), Ce2Mn(CO3)(Si2O7) and biraite-(La), La2Fe2+(CO3)(Si2O7), three new isostructural minerals and a definition of the biraite group

Authors	KASATKIN Anatoly V. ZUBKOVA Natalia V. PEKOV Igor V. CHUKANOV Nikita V. ŠKODA Radek AGAKHANOV Atali A. BELAKOVSKIY Dmitriy I. BRITVIN Sergey N. PUSHCHAROVSKY Dmitry Yu.
Year of publication	2021
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-iv-alexkuznetsovitela-la2mnco3si2o7-alexkuznetsovitece-ce2mnco3si2o7-and-biraitela-la2fe2co3si2o7-three-n
Doi	http://dx.doi.org/10.1180/mgm.2021.64
Keywords	alexkuznetsovite-(La); alexkuznetsovite-(Ce); biraite-(La); new mineral; rare-earth carbonate-silicate; crystal structure; biraite group; Mochalin Log; South Urals
Description	Three new isostructural minerals, alexkuznetsovite-(La), ideally La2Mn(CO3)(Si2O7), alexkuznetsovite-(Ce) Ce2Mn(CO3)(Si2O7) and biraite-(La) La2Fe2+(CO3)(Si2O7), were discovered in polymineralic nodules from the Mochalin Log REE deposit, South Urals, Russia. The new minerals form anhedral grains up to 0.3 mm x 0.4 mm [alexkuznetsovite-(La)], 0.5 mm x 0.9 mm [alexkuznetsovite-(Ce)] and 0.2 mm x 1.2 mm [biraite-(La)] embedded in granular aggregates consisting of different REE minerals [allanite-(Ce)/-(La), bastnasite-(Ce)/-(La), fluorbritholite-(Ce), perbOeite-(Ce)/-(La), percleveite-(Ce)/-(La) and tornebohmite-(Ce)/-(La)]. All three new species are brown to dark brown, translucent in thin fragments, with white streak, vitreous lustre and Mohs' hardness of similar to 5. D-calc = 4.713 [alexkuznetsovite-(La)], 4.687 [alexkuznetsovite-(Ce)] and 4.682 [biraite-La)] g.cm(-3). Their empirical formulae, calculated on the basis of 2 Si and 10 O apfu, are: alexkuznetsovite-(La): (La0.98Ce0.89Nd0.10Pr0.05)(Sigma 2.02)Mn0.502+Fe0.292+Ca0.12Mg0.03(CO3)(0.94)(HCO3)(0.06) (Si2O7); alexkuznetsovite-(Ce): (Ce0.96La0.78Nd0.16Pr0.07)(Sigma 1.97)Th0.01Mn0.502+Fe0.332+Ca0.14Mg0.02(CO3)(0.93)(HCO3)(0.07)(Si2O7); and biraite-(La): (La0.95Ce0.87Nd0.08Pr0.04)(Sigma 1.94)Th0.01Ca0.12Fe0.442+Mn0.382+Mg0.07(CO3)(0.88)(HCO3)(0.12)(Si2O7). The new minerals are monoclinic, P2(1)/c and Z = 4. The unit-cell parameters of alexkuznetsovite-(La)/alexkuznetsovite-(Ce)/biraite-(La) are: a = 6.5642(3)/6.5764(4)/6.5660(10), b = 6.7689(3)/6.7685(4)/6.7666(11), c = 18.7213(10)/18.7493(15)/18.698(3) angstrom, beta = 108.684(6)/108.672(8)/108.952(16)degrees and V = 788.00(7)/790.66(10)/785.7(2) angstrom(3). The crystal structures are solved from single-crystal X-ray diffraction data; R = 0.0628 [alexkuznetsovite-(La)], 0.0589 [alexkuznetsovite-(Ce)] and 0.1193 [biraite-(La)]. A new biraite group is defined; it includes isostructural biraite-(Ce) and the three new minerals described herein. The rootname alexkuznetsovite is given in honour of the Russian mineral collector Alexey M. Kuznetsov (born 1962) who provided samples in which all three new minerals were found. The Levinson's suffix-modifier -(La) or -(Ce) indicates the predominance of La or Ce among REE in the mineral. Biraite-(La) is named as an analogue of biraite-(Ce) with La prevailing among REE.