Abstract: Ferrous substituted saléeite is a new variety of saléeite from Arcu su Linnarbu, Sardinia. It is tetragonal with a = 6.982(2) c = 19.660(2) Å, Z = 2; the ideal formula is (Mg,Fe²⁺)(UO₂)₂(PO₄)₂·4H₂O. The strongest lines in the X-ray powder diffraction pattern are: 3.473(100)(114), 4.95(50)(110), 4.91(40)(004), 4.443(40)(112), 2.200(30)(118), 2.193(30)(303) and 2.178(30)(009). The mineral is light-yellow in colour and is dull fluorescent. The measured density is 3.242 g/cm³ and Z = 2. There is a prominent (001) cleavage. Refractive indices are : α = 1.572(2) β = 1.577(2) γ = 1.581(2) and 2V = 48°(2). The pleochroism is very weak and the elongation is positive parallel to Y. The mineral occurs as subparallel crystal aggregates with a quadratic outline.