Monazite-(Gd), ideally GdPO4, is a new mineral of the monazite group. It was discovered near Prakovce-Zimná Voda, ~23 km WNW of Košice, Western Carpathians, Slovakia. It forms anhedral domains (≤100 μm, mostly 10–50 μm in size), in close association with monazite-(Sm), Gd-bearing xenotime-(Y), Gd-bearing hingganite-(Y), fluorapatite and uraninite. All these minerals are hosted in a REE–U–Au quartz–muscovite vein, hosted in phyllites in an exocontact to granites. The density calculated using the average empirical formula and unit-cell parameters is 5.55 g/cm3. The average chemical composition measured by means of electron microprobe is as follows (wt.%): P2O5 29.68, As2O5 0.15, SiO2 0.07, ThO2 0.01, UO2 0.04, Y2O3 1.30, La2O3 3.19, Ce2O3 6.93, Pr2O3 1.12, Nd2O3 10.56, Sm2O3 17.36, Eu2O3 1.49, Gd2O3 22.84, Tb2O3 1.57, Dy2O3 2.27, CaO 0.21, total 99.67. The corresponding empirical formula calculated on the basis of 4 oxygen atoms is: (Gd0.30Sm0.24Nd0.15Ce0.10La0.05Dy0.03Y0.03Tb0.02Eu0.02Pr0.02Ca0.01)0.98P1.01O4. The ideal formula is GdPO4. The monazite-type structure has been confirmed by micro-Raman spectroscopy and selected-area electron diffraction. Monazite-(Gd) is monoclinic, space group P21/n, a = 6.703(1) Å, b = 6.914(1) Å, c = 6.383(1) Å, β = 103.8(1)°, V = 287.3(1) Å3 and Z = 4. The middle REE enrichment of monazite-(Gd) is shared with the associated Gd-bearing xenotime-(Y) to ‘xenotime-(Gd)’ and Gd-bearing hingganite-(Y). This exotic REE signature and precipitation of Gd-bearing mineral assemblage is a product of selective complexing and enrichment in middle REE in low-temperature hydrothermal fluids by alteration of primary uraninite, brannerite and fluorapatite on a micro-scale. The new mineral is named as an analogue of monazite-(La), monazite-(Ce), monazite-(Nd) and monazite-(Sm) but with Gd dominant among the REE.

独居石-(Gd)，理想的是GdPO 4，是独居石族的一种新矿物。它是在斯洛伐克西喀尔巴阡山脉科希策西北约 23 公里的 Prakovce-Zimná Voda 附近发现的。它形成上反角域（≤100μm，尺寸大多为10-50μm），与独居石（Sm）、含钆磷钇矿（Y）、含钆新辉石（Y）、氟磷灰石和铀矿密切相关。所有这些矿物都赋存于稀土-铀-金石英-白云母矿脉中，赋存于与花岗岩外接触的千枚岩中。使用平均经验公式和晶胞参数计算的密度为5.55g/cm 3。通过电子探针测得的平均化学成分如下（wt.%）：P 2 O 5 29.68、As 2 O 5 0.15、SiO2 0.07、ThO 2 0.01、UO 2 0.04、Y 2 O 3 1.30、La 2 O 3 3.19、Ce 2 O 3 6.93、Pr 2 O 3 1.12、Nd 2 O 3 10.56、Sm 2 O 3 17.36、Eu 2 O 3 1.49，Gd 2 O 3 22.84，Tb 2 O 3 1.57，Dy 2 O 3 2.27，CaO 0.21，总计99.67。以4个氧原子为基础计算出相应的经验公式为：（Gd0.30 Sm 0.24 Nd 0.15 Ce 0.10 La 0.05 Dy 0.03 Y 0.03 Tb 0.02 Eu 0.02 Pr 0.02 Ca 0.01 ) 0.98 P 1.01 O 4。理想的分子式是GdPO 4。显微拉曼光谱和选区电子衍射证实了独居石型结构。独居石-(Gd) 是单斜晶系，空间群P 2 1 / n , a = 6.703(1) Å, b = 6.914(1) Å, c= 6.383(1) Å, β = 103.8(1)°, V = 287.3(1) Å 3且 Z = 4。独居石-(Gd) 的中间 REE 富集与相关的含 Gd 磷钇矿-(Y) 共享) 至“磷钇矿-(Gd)”和含 Gd 的 Hingganite-(Y)。这种奇异的稀土元素特征和含钆矿物组合的沉淀是低温热液中中稀土元素通过微尺度蚀变原生铀矿、镁矿和氟磷灰石选择性络合和富集的产物。这种新矿物被命名为独居石-(La)、独居石-(Ce)、独居石-(Nd)和独居石-(Sm)的类似物，但在稀土元素中以Gd为主。