Publication details

The mineralogy of the historical Mochalin Log REE deposit, South Urals, Russia. Part I. New gatelite-group minerals ferriperboeite-(La), (CaLa3)(Fe3+Al2Fe2+)[Si2O7][SIO4](3)O(OH)(2) and perboeite-(La), (CaLa3)(Al3Fe2+)[Si2O7][SiO4](3)O(OH)(2)

Authors	KASATKIN Anatoly V. ZUBKOVA Natalia V. PEKOV Igor V. CHUKANOV Nikita V. ŠKODA Radek POLEKHOVSKY Yury S. AGAKHANOV Atali A. BELAKOVSKIY Dmitriy I. KUZNETSOV Aleksey M. BRITVIN Sergey N. PUSHCHAROVSKY Dmitry Yu.
Year of publication	2020
Type	Article in Periodical
Magazine / Source	Mineralogical Magazine
MU Faculty or unit	Faculty of Science
Citation
Web	https://doi.org/10.1180/mgm.2020.42
Doi	http://dx.doi.org/10.1180/mgm.2020.42
Keywords	ferriperboeite-(La); perboeite-(La); new mineral; rare-earth silicate; crystal structure; gatelite group; Mochalin Log; South Urals
Description	The paper opens a series devoted to the mineral diversity of the Mochalin Log rare earth element (REE) deposit, South Urals, Russia. There is a brief outline of the history of studies and geology of the deposit as well as the description of two new isostructural gatelitegroup minerals, ferriperboeite-(La) (CaLa3)(Fe3+Al2Fe2+)[Si2O7][SiO4](3)O(OH)(2) and perboeite-(La) (CaLa3)(Al3Fe2+)[Si2O7][SiO4](3)O (OH)(2). Both minerals occur in polymineralic nodules and are associated with one another and allanite-(Ce), allanite-(La), bastnasite-(Ce), bastnasite-(La), ferriallanite-(Ce), ferriallanite-(La), ferriperboeite-(Ce), perboeite-(Ce), tornebohmite-(Ce) and tornebohmite-(La). The new minerals form isolated anhedral grains up to 0.3 mm [ferriperboeite-(La)] and 0.5 mm [perboeite-(La)] across and granular aggregates up to 1.5 mm x 0.5 mm Eferriperboeite-(La)] and 3 mm x 1 mm perboeite-(La)]. Both minerals are brownish-black with vitreous lustre. D-calc = 4.510 [ferriperboeite-(La)] and 4.483 [perboeite-(La)] g cm(-3). They are optically biaxial (+); ferriperboeite-(La): alpha = 1.788(5), beta = 1.790(5), gamma = 1.810(5) and 2V(meas) = 40(10)degrees; perboeite-(La): alpha = 1.778(8), beta = 1.783(8), gamma = 1.805(8) and 2V(meas) = 40(10)degrees. Chemical data [wt.%, electron-microprobe; Fe3+:Fe2+ ratio from charge-balance requirements, H2O by stoichiometry; ferriperboeite-(La)/perboeite-(La)] are: CaO 4.91/4.81, ThO2 0.00/0.32, La2O3 23.75/22.16, Ce2O3 19.69/20.05, Pr2O3 0.85/1.09, Nd2O3 1.48/2.18, MgO 1.47/1.38, Al2O3 10.68/11.25, MnO 1.07/0.92, FeO 3.04/3.35, Fe2O3 5.31/3.78, TiO2 0.19/0.19, SiO2 27.47/27.35, F 0.11/0.23, H2O 1.61/1.54, -O = F -0.05/-0.10, total 101.58/100.50. The empirical formulae based on O-20(OH,F)(2) are for ferriperboeite-(La): (Ca0.95La1.58Ce1.30Nd0.10Pr0.06)(Sigma 3.99)(Al2.27Fe0.723+Fe0.462+Mg0.40Mn0.16Ti0.03)(Sigma 4.04)Si(4.96)O20[(OH)(1.94)F(0.1)3]; and for perboeite-(La): (Ca0.94Th0.01La1.49Ce1.36Nd0.14Pr0.07)(Sigma 3.99) (Al(2.4)2Fe(0.52)(3+)Fe(0.51)(2+)Mg(0.38)Mn(0.14) Ti-0.03)(Sigma 4.00)Si4.99O20[(OH)(1.87)F-0.13].( )Both minerals are monoclinic, P2(1)/m; the unit-cell parameters Iferriperboeite-(La)/perboeite-(La)] are a = 8.9458(2)/8.9652(4), b= 5.72971(13)/5.7306(2), c= 17.6192(3)/17.6770(9) angstrom, beta = 115.9497(19)/116.053(6)degrees, V= 812.06(3)/815.88(6)angstrom(3) and Z = 2/2. The crystal structures are solved on a single crystal and converged to R= 0.0355 [ferriperboeite-(La)] and 0.0750 [perboeite-(La)]. Ferriperboeite-(La) and perboeite-(La) are named as the La-analogues of ferriperboeite-(Ce) and perboeite-(Ce), respectively.