Zinkgruvanite, Ba<sub>4</sub>Mn<sup>2+</sup><sub>4</sub>Fe<sup>3+</sup><sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>O<sub>2</sub>(OH)<sub>2</sub>, a new ericssonite-group mineral from the Zinkgruvan Zn-Pb-Ag-Cu deposit, Askersund, Örebro County, Sweden

Abstract. Zinkgruvanite, ideally Ba4Mn42+Fe23+(Si2O7)2(SO4)2O2(OH)2, is a new member of the ericssonite group, found in Ba-rich drill core samples from sphalerite- and galena- diopside-rich metatuffite succession Zinkgruvan mine, Örebro County, Sweden. Zinkgruvanite associated with massive baryte, barytocalcite, diopside minor witherite, cerchiaraite-Al, sulfide minerals. It occurs as subhedral to euhedral flattened elongated crystals up 4 mm. almost black semi-opaque dark-brown streak. The lustre vitreous sub-adamantine on crystal faces resinous fractures. mineral brittle an uneven fracture. VHN100=539, HMohs ≈ 4.5. In thin fragments, it reddish-black, translucent optically biaxial (+), 2Vz > 70∘. Pleochroism strong deep brown-red (E ⊥ {001} cleavage) olive-pale-brown. Chemical point analyses by WDS-EPMA (wavelength-dispersive X-ray spectroscopy electron probe microanalyser) together iron valencies determined Mössbauer yielded empirical formula (based 26 O+OH+F+Cl anions): (Ba4.02Na0.03)Σ4.05(Mn1.79Fe1.562+Fe0.423+Mg0.14Ca0.10Ni0.01Zn0.01)Σ4.03(Fe1.743+Ti0.20Al0.06)Σ2.00Si4(S1.61Si0.32P0.07)Σ1.99O24(OH1.63Cl0.29F0.08)Σ2.00. triclinic, space group P1¯, unit-cell parameters a=5.3982(1) Å, b=7.0237(1) c=14.8108(4) α= 98.256(2)∘, β= 93.379(2)∘, γ= 89.985(2)∘ V= 554.75(2) Å3 for Z=1. eight strongest powder diffraction lines are following (d Å (I %; hkl)): 3.508 (70; 103), 2.980(70; 114‾), 2.814 (68; 12‾2), 2.777 121), 2.699 (714; 200), 2.680 201‾), 2.125 (100; 124, 204) 2.107 (96; 2‾21). structure (R1=0.0379 3204 reflections) array TS (titanium silicate) blocks alternating intermediate blocks. consist HOH sheets (H heteropolyhedral O octahedral) parallel (001). sheet, Mn2+-dominant MO(1,2,3) sites give Mn42+ pfu (per unit). H Fe3+-dominant MH AP(1) Fe23+Ba2 pfu. block, SO4 oxyanions 11 coordinated Ba atoms 2× SO4Ba related ferroericssonite having same topology type linkage layers block. also closely compositionally yoshimuraite, Ba4Mn4Ti2(Si2O7)2(PO4)2O2(OH)2, via coupled heterovalent substitution 2 Ti4++ (PO4)3-→2 Fe3++ (SO4)2− but presents different linkage. probably formed during late stage regional metamorphism Ba-enriched, syngenetic protolith, involving locally generated oxidized fluids high salinity.