Abstract 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), bastnäsite-(Ce), bastnäsite-(La), ferriallanite-(Ce), ferriallanite-(La), ferriperbøeite-(Ce), ferriperbøeite-(La), fluorbritholite-(Ce), hydroxylbastnäsite-(Ce), perbøeite-(Ce), perbøeite-(La), törnebohmite-(Ce) and törnebohmite-(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 ɛ = 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.

中文翻译：

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俄罗斯南乌拉尔历史 Mochalin Log REE 矿床的矿物学。第三部分。Percleveite-(La), La2Si2O7, 一种新型稀土二硅酸盐矿物

摘要 在俄罗斯南乌拉尔州车里雅宾斯克州 Mochalin Log REE 矿床的多矿物结核中发现了新矿物 percleveite-(La) (IMA2019-037)，理想的是 La2Si2O7。它与allanite-(Ce)、allanite-(La)、bastnäsite-(Ce)、bastnäsite-(La)、ferriallanite-(Ce)、ferriallanite-(La)、ferriperbøeite-(Ce)、ferriperbøeite-(La ), 萤石-(Ce), 羟基菱镁矿-(Ce), perbøeite-(Ce), perbøeite-(La), törnebohmite-(Ce) 和 törnebohmite-(La)。Percleveite-(La) 以孤立的无面体晶粒形式出现，通常高达 0.2 mm × 0.4 mm，很少达到 1 mm × 1 mm。新矿物透明，有油脂光泽。矿物呈淡黄色至无色，呈细碎片状，呈淡黄色状。它很脆，具有不完美的 {001} 解理和不均匀的断裂。莫氏硬度约为。6. Dcalc = 5.094 g cm–3。在显微镜下，percleveite-(La) 是非多向色的，光学单轴 (+)，ω = 1.825(10) 和 ɛ = 1.835(10)。给出了拉曼光谱。化学数据（重量百分比，电子探针）为：La2O3 36.80、Ce2O3 31.22、Pr2O3 1.57、Nd2O3 2.96、SiO2 26.73，总计 99.28。基于 7 O apfu 的经验公式为 (La1.02Ce0.86Nd0.08Pr0.04)Σ2.00Si2.00O7。Percleveite-(La)是四方晶，P41；晶胞参数为：a = 6.8482(3), c = 24.8550(13) Å, V = 1165.64(11) Å3 和 Z = 8. 粉末 X 射线衍射图中最强的反射 [d, Å( I)(hkl)] 是： 4.194(18)(113), 3.564(16)(106), 3.349(16)(201,202), 3.157(100)(203,116,008), 3.023(19,22) 39)(122)、2.893(29)(213) 和 2.864(21)(117)。从单晶 X 射线衍射数据 [R = 0. 0617 用于 2831 次独特的反射，其中 I > 2σ(I)]。这种新矿物被命名为 percleveite-(Ce) 的类似物，其中 La 在稀土元素上占优势。