Skogbyite, Zr(Mg2Mn3+4)SiO12, a new zirconium mineral in the braunite group from Långban, Bergslagen, Sweden

Skogbyite, ideally Zr(Mg2Mn34+)SiO12, is a new mineral species (IMA 2023-085) within the braunite group, discovered in a complex metamorphic assemblage from the Långban Fe–Mn oxide deposit, Värmland County, Bergslagen ore province, Sweden. It is named after the Swedish mineralogist Henrik Skogby (b. 1956). The new mineral is hosted by a hausmannite–jacobsite-bearing calcite–dolomite–phlogopite rock that additionally contains pinakiolite, macedonite and sparse baddeleyite. In this assemblage, skogbyite occurs as very small, mostly ≤ 60 µm, rounded to subhedral grey crystals. It is suggested that skogbyite formed during regional metamorphism of a pre-existing, weakly Mn(–Fe)-mineralised carbonate–silicate rock. Optically, the mineral is opaque and bluish grey with a moderate reflectance in reflected polarised light and exhibits weak bireflectance and anisotropy. The Mohs hardness is estimated to be 6–6.5, and it has a calculated density of 4.821 g cm−3. Skogbyite is tetragonal, space group I41/acd, with unit-cell parameters a = 9.4914(4) Å, c = 18.9875(10) Å, V = 1710.52(17) Å3 and Z = 8. Its crystal structure was refined to R1 = 0.0460 for 648 unique reflections with I >2σI, collected utilising MoKα X-ray radiation. The five strongest (calculated) powder X-ray diffraction lines (d in Å, (I), (hkl)) are 2.740, (100), (224); 1.678, (31), (048); 1.431, (16), (264); 1.678, (13), (440); and 5.480, (12), (112). Electron probe microanalyses combined with single-crystal structure refinement resulted in the following empirical formula: (Zr40+69Ce30+10Mg0.06Ca0.01Zn0.01Pb0.01)60.87(Mn34+23Mg1.40Fe30+28Al0.09)66.00Si1.04O12 based on 12 O atoms. All Mn in the new mineral is trivalent. Skogbyite is related to gatedalite, Zr(Mn2Mn34+)SiO12, by the substitution Mn2+Mg−1. Skogbyite is abbreviated as “Skb”.