Redefinition of beraunite, Fe<sup>3+</sup><sub>6</sub>(PO<sub>4</sub>)<sub>4</sub>O(OH)<sub>4</sub> ⋅ 6H<sub>2</sub>O, and discreditation of the name eleonorite: a re-investigation of type material from the Hrbek Mine (Czech Republic)

Abstract. Re-investigation of the type material beraunite from Hrbek Mine, Svatá Dobrotivá, Czech Republic, proved identity and eleonorite. Based on this study, mineral eleonorite was discredited, ideal formula redefined Fe2+Fe53+(PO4)4(OH)5 ⋅ 6H2O to Fe63+(PO4)4O(OH)4 6H2O. Beraunite Mine usually forms prismatic crystals flattened {100}; elongated along b axis, striated {100} || b, up 0.2 × 0.5 3 mm, often in radial clusters 6 mm size association with black goethite, olive-green dark green dufrénite yellow orange cacoxenite. is hyacinth red, or red-brown has a light orange-red streak; are translucent, vitreous luster. The symmetry structure found be lower (Cc) than reported past (C2/c); been proven by crystal refinement, Robs= 2.7 % for Cc ∼ 8 C2/m. Refined unit-cell parameters obtained powder X-ray diffraction data original Friedrich August Breithaupt a= 20.653(2), b= 5.1433(6), c= 19.241(2) Å, β=93.560(9)∘, V= 2039.9(2) Å3. Calculated density 2.961 g cm−3. optically biaxial (+), α= 1.768(2), β= 1.781(3), γ>1.805, 2Vmeas= 69(4)∘, 2Vcalc not possible calculate. Dispersion optical axes strong, r>v. orientation Y=b, X≈a, Z≈c. Pleochroism strong; Z (brown-red) ≫Y>X (both brownish yellow). empirical sample calculated basis P = 4 apfu (Fe5.763+Al0.15Zn0.01)5.92(PO4)4.00O0.99(OH)3.77 57Fe Mössbauer spectrum neotype (National Museum, Prague) locality implies that all iron atoms exclusively trivalent, located at M site different next-nearest-neighbor configurations. There no spectral evidence Fe2+ some impurities (e.g., limonite).