Jagoite, nominal formula Pb₁₁Fe₅Si₁₂O₄₁Cl₃, was described in 1957 by Blix et al. It is only known from the Långban and Pajsberg Fe-Mn deposits, in the Filipstad district, Värmland, Sweden. The crystal structure was solved by Mellini & Merlino in 1981. We have reinvestigated the mineral in samples from both localities. The crystal structure was refined (R1 = 1.2% for 2090 reflections with Fo > 4σ(Fo)) from type material and the original structural model is essentially confirmed. Chemical analyses indicate that Al³⁺ could substitute for Fe³⁺ in jagoite, up to 2.3 wt. % Al₂O₃; Mn and Zn is also present in some samples (up to 1.7 wt.% Mn₂O₃ and 1.2 wt.% ZnO, respectively). Two tetrahedrally coordinated sites have unusually short bonds, which may indicate substitution of Si by a small cation like B³⁺. Pb and Cl show stable concentration values and jagoite is essentially anhydrous. ⁵⁷Fe Mössbauer data have been collected from a powder absorber. The hyperfine parameters are consistent with Fe being present only in trivalent form (high spin), and distributed over a relatively regular 6-coordinated site and distorted 4-coordinated sites. Distinct Raman bands appear at 183, 222, 340, 524, 635, 680, 860, 885, 925, 952, 985 and 1050 cm^-1. Jagoite occurs in a skarn assemblage with andradite, diopside, hematite, quartz, together with the Pb silicates alamosite, barysilite, jagoite, joesmithite, melanotekite, nasonite and yangite. Jagoite is the mineral most susceptible to hydrothermal alteration in this association, forming new, poorly known phases in the system CaO-PbO-SiO₂-H₂O-Cl₂.