Jahnsite-(CaMnMn), a new mineral species from Mangualde, Beira, Portugal, occurs as equant, brownish yellow crystals to 0.5 mm, associated with phosphosiderite, zodacite, varulite, and microcline. The mineral is transparent and has a vitreous luster. It is brittle with a poor parting on {001} and has a hardness of approximately 4 (Mohs). Dobs = 2.78(8) and Dcalc = 2.798 g/cm3. Optically it is biaxial negative, α = 1.643(1), β = 1.659(1), γ = 1.671(1), 2Vmeas = 80(2)°, 2Vcalc = 81°. It is monoclinic with possible space groups P2/a or Pa, a = 14.887(8), b = 7.152(7), c = 9.966(6) Å, β = 109.77(5)°, and Z = 2. The strongest X-ray powder diffraction lines are [d(Å), I, hkl] 9.40 (10) (001), 5.74 (2) (111, 011), 5.02(2) (210), 4.971 (2) (102), 4.704 (3) (202, 002), 3.532 (2) (312), 3.463 (2) (120), 2.986 (213, 113), 2.870 (8) (313), and 2.608 (2) (510). Electron microprobe and TGA analyses gave Al2O3 0.7, Fe2O3 21.5, MgO 0.5, CaO 5.8, MnO 20.2, P2O5 34.3, H2O 18.5, total 101.5 wt%, which yields the formula Ca0.86Mn0.80(Mn1.56Fe0.34Mg0.10)Σ2(Fe1.893+Al0.11)Σ2(PO4)4(OH)1.667.67H2O or ideally CaMnMn2Fe23+(PO4)4(OH)28H2O, based on 4 P atoms.

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