Iseite, Mn₂Mo₃O₈, a new mineral from Ise, Mie Prefecture, Japan

抄録

Iseite, Mn₂Mo₃O₈, a new mineral that is a Mn-dominant analogue of kamiokite, is found in the stratiform ferromanganese deposit, Shobu area, Ise City, Mie Prefecture, Japan. It is the first mineral species that includes both Mn and Mo as essential constituents. Iseite is iron-black in color and has a submetallic luster. It occurs as aggregates up to about 1 mm in size made of minute crystals (<20 μm). Iseite has a zoned structure closely associated with undetermined Mn-Fe-Mo oxide minerals with hexagonal forms, and it occasionally coexists with small amounts of powellite. Its Mohs hardness is 4-5, and its calculated density is 5.85 g/cm³. The empirical formula of iseite is (Mn_1.787Fe_0.193)_Σ1.980Mo_3.010O₈. Its simplified ideal formula is written as Mn₂Mo₃O₈. The mineral is isostructural with kamiokite (hexagonal, P6₃mc). The unit cell parameters are a = 5.8052 (3) Å, c = 10.2277 (8) Å, V = 298.50 (4) ų, and Z = 2. The Rietveld refinement using synchrotron radiation (λ = 0.413 Å) powder XRD data converges to R_wp = 3.11%, and confirms two independent Mn sites—tetrahedral and octahedral—in the crystal structure of iseite, indicating the structure formula Mn^IVMn^VIMo₃O₈.