Publication details

The mineralogy of the historical Mochalin Log REE deposit, South Urals, Russia. Part III. Percleveite-(La), La2Si2O7, a new REE disilicate mineral

Authors

KASATKIN Anatoly V. ZUBKOVA Natalia V. PEKOV Igor V. CHUKANOV Nikita V. ŠKODA Radek AGAKHANOV Atali A. BELAKOVSKIY Dmitriy I. KSENOFONTOV Dmitriy A. PLÁŠIL Jakub 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.2020.81
Doi http://dx.doi.org/10.1180/mgm.2020.81
Keywords crystal structure; Mochalin Log; new mineral; percleveite-(La); Raman spectrum; rare-earth disilicate; South Urals
Description The new mineral percleveite-(La) (IMA2019-037), ideally La2Si2O7, was found in polymineralic nodules of the Mochalin Log REE deposit, Chelyabinsk Oblast, South Urals, Russia. It is associated with allanite-(Ce), allanite-(La), bastnasite-(Ce), bastnasite-(La), ferriallanite-(Ce), ferriallanite-(La), ferriperbOeite-(Ce), ferriperbOeite-(La), fluorbritholite-(Ce), hydroxylbastnasite-(Ce), perbOeite-(Ce), perbOeite-(La), tornebohmite-(Ce) and tornebohmite-(La). Percleveite-(La) occurs as isolated anhedral grains commonly up to 0.2 mm x 0.4 mm and very rarely up to 1 mm x 1 mm. The new mineral is transparent with greasy lustre. The mineral is very pale yellow to colourless in thin fragments to light yellow in aggregates. It is brittle, with imperfect {001} cleavage and an uneven fracture. Mohs' hardness is ca. 6. D-calc = 5.094 g cm(-3). Under the microscope, percleveite-(La) is non-pleochroic, optically uniaxial (+), omega = 1.825(10) and = 1.835(10). The Raman spectrum is given. Chemical data (wt.%, electron-microprobe) are: La2O3 36.80, Ce2O3 31.22, Pr2O3 1.57, Nd2O3 2.96, SiO2 26.73, total 99.28. The empirical formula based on 7 O apfu is (La1.02Ce0.86Nd0.08Pr0.04)(Sigma 2.00)Si2.00O7. Percleveite-(La) is tetragonal, P4(1); the unit-cell parameters are: a = 6.8482(3), c = 24.8550(13) angstrom, V = 1165.64(11) angstrom(3) and Z = 8. The strongest reflections in the powder X-ray diffraction pattern [d, angstrom(I)(hkl)] are: 4.194(18)(113), 3.564(16)(106), 3.349(16)(201,202), 3.157(100)(203,116,008), 3.043(22)(211), 2.934(39)(122), 2.893(29)(213) and 2.864(21)(117). The crystal structure of percleveite-(La) is solved from the single-crystal X-ray diffraction data [R = 0.0617 for 2831 unique reflections with I > 2 sigma(I)]. The new mineral is named as an analogue of percleveite-(Ce) with La predominance over the rare-earth elements.

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