Abstract. Clino-ferro-suenoite, with the ideal formula □Mn₂Fe²⁺₅Si₈O₂₂(OH)₂, previously named “dannemorite” or “manganogrunerite”, is formally recognized as a monoclinic member of the amphibole supergroup (IMA-CNMMC 2024-032). It occurs in iron-manganese skarn from the Hilläng mines, Dalarna, Sweden, associated with fayalite, spessartine, ferro-actinolite, calcite, magnetite and pyrite. It formed by partial replacement of manganoan fayalite during retrograde metamorphism. Individual crystals, up to 0.5 mm in length, are subhedral with a pale greenish yellow colour. The mineral is non-pleochroic and optically biaxial (–), with α = 1.670(5), β = 1.690(5), γ = 1.705(5); orientation Y || b, Z ⋀ c = 14(1)°. Cleavage parallel {110} and {010} is perfect and good, respectively. The Mohs hardness is about 6 and the mean Vickers hardness number was established as 872. The calculated density value is 3.46(1) g·cm^-3. The crystal-chemical formula of clino-ferro-suenoite is ^A□^B(Mn²⁺_0.95Fe²⁺_0.88Ca_0.15Na_0.01)_Σ1.99 ^C(Fe²⁺_3.57Mg_1.38 Mn²⁺_0.03Zn_0.01Al_0.01)_Σ5.00 ^TSi_8.00O₂₂ ^W[(OH)_1.99F_0.01]_Σ2.00, based on microprobe analyses, spectroscopic data (Mössbauer, infra-red, Raman) and a single-crystal X-ray diffraction study. Infra-red bands originating from O-H vibration modes appear at 3608, 3620, 3638, 3653 and 3668 cm^-1, with the first and last one having weak intensities. The seven strongest reflections in the X-ray powder pattern [d values (in Å), I_rel, (hkl)] are: 8.33, 100, (110); 3.278, 21, (240); 3.084, 72, (310); 2.784, 18, (330); 2.512, 19, (20-2); 1.526, 16, (0.12.0); 1.412, 19, (66-1). Unit-cell parameters obtained from single-crystal diffraction data (MoKα) are a = 9.59840(10), b = 18.3179(2), c = 5.33450(10) Å, β = 102.1630(10)° and V = 916.87(2) ų for Z = 2. Refinement of the crystal structure in the space group C2/m yielded R = 2.25% for 1379 reflections with Io > 2σ(I). Mg ions show preference for the octahedrally coordinated C sites in the order M(2) > M(1) > M(3).