Details

Autor(en) / Beteiligte

• Kasatkin, Anatoly V
• Zubkova, Natalia V
• Pekov, Igor V
• Chukanov, Nikita V
• Skoda, Radek
• Agakhanov, Atali A
• Belakovskiy, Dmitriy I
• Ksenofontov, Dmitriy A
• Plasil, Jakub
• Kuznetsov, Aleksey M
• Britvin, Sergey N
• Pushcharovsky, Dmitry Yu

Titel

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

Ist Teil von

• Mineralogical magazine, 2020-12, Vol.84 (6), p.913-920

Ort / Verlag

London: Mineralogical Society

Erscheinungsjahr

2020

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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×0.4 mm and very rarely up to 1 mm×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. Dcalc=5.094 g cm-3. Under the microscope, percleveite-(La) is non-pleochroic, optically uniaxial (+), ω=1.825(10) and ε=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)Σ2.00Si2.00O7. Percleveite-(La) is tetragonal, P41; the unit-cell parameters are: a=6.8482(3), c=24.8550(13) Å, V=1165.64(11) Å3 and Z=8. The strongest reflections in the powder X-ray diffraction pattern [d, Å(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>2σ(I)]. The new mineral is named as an analogue of percleveite-(Ce) with La predominance over the rare-earth elements.