| Summary: | The new mineral species rüdlingerite, ideally Mn<sup>2+</sup><sub>2</sub>V<sup>5+</sup>As<sup>5+</sup>O<sub>7</sub>·2H<sub>2</sub>O, occurs in the Fianel mine, in Val Ferrera, Grisons, Switzerland, a small Alpine metamorphic Mn deposit. It is associated with ansermetite and Fe oxyhydroxide in thin fractures in Triassic dolomitic marbles. Rüdlingerite was also found in specimens recovered from the dump of the Valletta mine, Canosio, Cuneo, Piedmont, Italy, where it occurs together with massive braccoite and several other As- and V-rich phases in richly mineralized veins crossing the quartz-hematite ore. The new mineral displays at both localities yellow to orange, flattened elongated prismatic, euhedral crystals measuring up to 300 μm in length. Electron-microprobe analysis of rüdlingerite from Fianel gave (in wt%): MnO 36.84, FeO 0.06, As<sub>2</sub>O<sub>5</sub>, 25.32, V<sub>2</sub>O<sub>5</sub> 28.05, SiO<sub>2</sub> 0.13, H<sub>2</sub>O<sub>calc</sub> 9.51, total 99.91. On the basis of 9 O anions per formula unit, the chemical formula of rüdlingerite is Mn<sub>1.97</sub>(V<sup>5+</sup><sub>1.17</sub> As<sub>0.83</sub>Si<sub>0.01</sub>)<sub>Σ2.01</sub>O<sub>7</sub>·2H<sub>2</sub>O. The main diffraction lines are [<i>d<sub>obs</sub></i> in Å (<i>I<sub>obs</sub></i>) <i>hkl</i>]: 3.048 (100) 022, 5.34 (80) 120, 2.730 (60) 231, 2.206 (60) 16-1, 7.28 (50) 020, 2.344 (50) 250, 6.88 (40) 110, and 2.452 (40) 320. Study of the crystal structure showcases a monoclinic unit cell, space group <i>P</i>2<sub>1</sub><i>/n</i>, with <i>a</i> = 7.8289(2) Å, <i>b</i> = 14.5673(4) Å, <i>c</i> = 6.7011(2) Å, <i>β</i> = 93.773(2)°, <i>V</i> = 762.58(4) Å<sup>3</sup>, <i>Z</i> = 4. The crystal structure has been solved and refined to <i>R</i><sub>1</sub> = 0.041 on the basis of 3784 reflections with <i>F</i><sub>o</sub> > 4σ(<i>F</i>). It shows Mn<sup>2+</sup> hosted in chains of octahedra that are subparallel to [-101] and bound together by pairs of tetrahedra hosted by V<sup>5+</sup> and As<sup>5+</sup>, building up a framework. Additional linkage is provided by hydrogen-bonding through H<sub>2</sub>O coordinating Mn<sup>2+</sup> at the octahedra. One tetrahedrally coordinated site is dominated by V<sup>5+</sup>, <i><sup>T</sup></i><sup>(1)</sup>(V<sub>0.88</sub>As<sub>0.12</sub>), corresponding to an observed site scattering of 24.20 electrons per site (eps), whereas the second site is strongly dominated by As<sup>5+</sup>,<i><sup> T</sup></i><sup>(2)</sup>(As<sub>0.74</sub>V<sub>0.26</sub>), with, accordingly, a higher observed site scattering of 30.40 eps. The new mineral has been approved by the IMA-CNMNC and named for Gottfried Rüdlinger (born 1919), a pioneer in the 1960–1980s, in the search and study of the small minerals from the Alpine manganese mineral deposits of Grisons.
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