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 × 0.4 mm [alexkuznetsovite-(La)], 0.5 mm × 0.9 mm [alexkuznetsovite-(Ce)] and 0.2 mm × 1.2 mm [biraite-(La)] embedded in granular aggregates consisting of different REE minerals [allanite-(Ce)/-(La), bastnäsite-(Ce)/-(La), fluorbritholite-(Ce), perbøeite-(Ce)/-(La), percleveite-(Ce)/-(La) and törnebohmite-(Ce)/-(La)]. All three new species are brown to dark brown, translucent in thin fragments, with white streak, vitreous lustre and Mohs’ hardness of ~5. Dcalc = 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)Σ2.02Mn2+0.50Fe2+0.29Ca0.12Mg0.03(CO3)0.94(HCO3)0.06 (Si2O7); alexkuznetsovite-(Ce): (Ce0.96La0.78Nd0.16Pr0.07)Σ1.97Th0.01Mn2+0.50Fe2+0.33Ca0.14Mg0.02(CO3)0.93(HCO3)0.07(Si2O7); and biraite-(La): (La0.95Ce0.87Nd0.08Pr0.04)Σ1.94Th0.01Ca0.12Fe2+0.44Mn2+0.38Mg0.07(CO3)0.88(HCO3)0.12(Si2O7). The new minerals are monoclinic, P21/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) Å, β = 108.684(6)/108.672(8)/108.952(16)° and V = 788.00(7)/790.66(10)/785.7(2) Å3. 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.

三种新的同构矿物，alexkuznetsovite-(La)，理想情况下是 La 2 Mn(CO 3 )(Si 2 O 7 )，alexkuznetsovite-(Ce) Ce 2 Mn(CO 3 )(Si 2 O 7 ) 和 biraiite-(La) La 2 Fe 2+ (CO 3 )(Si 2 O 7 )，是在俄罗斯南乌拉尔Mochalin Log REE矿床的多矿物结核中发现的。新矿物形成嵌入粒状聚集体的最大0.3 mm × 0.4 mm [alexkuznetsovite-(La)]、0.5 mm × 0.9 mm [alexkuznetsovite-(Ce)]和0.2 mm × 1.2 mm [biraite-(La)]的正面体颗粒由不同的稀土矿物 [allanite-(Ce)/-(La), 氟碳铈矿-(Ce)/-(La), 萤石-(Ce), perbøeite-(Ce)/-(La), percleveite-(Ce)/-( La) 和 törnebohmite-(Ce)/-(La)]。所有三个新种都是棕色到深棕色，半透明的细碎片，有白色条纹，玻璃光泽，莫氏硬度为~5。D calc = 4.713 [alexkuznetsovite-(La)]、4.687 [alexkuznetsovite-(Ce)] 和 4.682 [biraite-La)] g⋅cm –3。他们根据 2 Si 和 10 O apfu 计算的经验公式是： alexkuznetsovite-(La): (La 0.98 Ce 0.89 Nd 0.10 Pr 0.05 ) Σ2.02 Mn 2+ 0.50 Fe 2+ 0.29 Ca0.12 Mg 0.03 (CO 3 ) 0.94 (HCO 3 ) 0.06 (Si 2 O 7 )；alexkuznetsovite-（铈）：（铈0.96的La 0.78的Nd 0.16镨0.07）Σ1.97钍0.01的Mn 2+ 0.50的Fe 2+ 0.33钙0.14镁0.02（CO 3）0.93（HCO 3）0.07（SI 2 ö 7）; 和 biraite-(La): (La 0.95 Ce0.87 Nd 0.08 Pr 0.04 ) Σ1.94 Th 0.01 Ca 0.12 Fe 2+ 0.44 Mn 2+ 0.38 Mg 0.07 (CO 3 ) 0.88 (HCO 3 ) 0.12 (Si 2 O 7 )。新矿物为单斜晶系，P 2 1 / c，Z = 4。alexkuznetsovite-(La)/alexkuznetsovite-(Ce)/biraite-(La)的晶胞参数为：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) 埃，β = 108.684(6)/108.61(10)/18.7493(15)/18.698(3) Å，β = 108.684(6)/108.61(10)/18.7493(15)/18.698(3) 5 ° 和V = 788.00(7)/790.66(10)/785.7(2) Å 3。晶体结构由单晶 X 射线衍射数据求解；R = 0.0628 [alexkuznetsovite-(La)]、0.0589 [alexkuznetsovite-(Ce)] 和 0.1193 [biraite-(La)]。定义了一个新的 biraiite 组；它包括等结构的菱铁矿-(Ce) 和本文所述的三种新矿物。根名 alexkuznetsovite 是为了纪念俄罗斯矿物收藏家 Alexey M. Kuznetsov（生于 1962 年），他提供了发现所有三种新矿物的样本。Levinson 的后缀修饰符 -(La) 或 -(Ce) 表示在REE中 La 或 Ce 占优势在矿物中。Biraite-(La)被命名为biraite-(Ce)的类似物，其中La在REE中占优势。