Zodacite, the Mn analogue of montgomeryite, from Mangualde, Portugal

Zodacite is a new Mn-dominant member of the montgomeryite group. Microprobe analysis yielded MgO 0.2, MnO 4.8, CaO 18.0, A1₂O₃ 7.7, Fe₂O₃ 14.1, P₂O₅ 34.8, H₂O (by difference) 20.4, total = 100.0 wt%. The idealized formula is Ca₄Mn$Fe43+$(PO₄)₆(OH)₄ · 12H₂O. Zodacite is monoclinic, C2/c or Cc, with a = 10.152(8), b = 24.14(3), c = 6.308(6) Å, β = 91.14(7)°, and Z = 2. The strongest diffractions in the powder pattern are [d_obs,I_obs,hkl] 5.18(10)(111), 12.00(6)(020), 2.907(5)(171), 3.150(4)(002,260), and 2.656(4)(202). Zodacite occurs as individual yellow crystals and as aggregates of radiating crystals, with a density of 2.68 g/cm³ (meas.) and 2.65 g/cm³ (calc.). It is biaxial, negative, 2V = 83°, with α = 1.598, β = 1.601, and γ = 1.602. Pleochroism is weak: Y = very pale green and Z = pale green; orientation is X = b, Y ∧ c = 24°, Z ∧ a = 23°. Zodacite is found associated with a Mn-rich jahnsite-group mineral, phosphosiderite, and hureaulite, on a specimen from the Mangualde pegmatite in Portugal. The name honors the late Peter Zodac, who inspired generations of mineralogists.