Abstract: Baghdadite, a new calcium zirconium silicate mineral has been found in melilite skarn in contact with banded diorite, from the Qala-Dizeh region, NE Iraq. Electron microprobe analysis yielded: SiO₂ = 29.26, ZrO₂ = 27.00, TiO₂ = 2.11, Fe₂O₃ = 0.11, Al₂O₃ = 0.03, MgO = 0.05, CaO = 41.44, Na₂O = 0.02, sum = 100.02 wt. %. The mineral contains about 0.16% HfO₂. This analysis calculates to Ca_3.00(Zr_0.89Ti_0.11)(Si_1.98Fe_0.01)O₉ which leads to the ideal formula Ca₃Zr[O₂|Si₂O₇]. X-ray single crystal study showed it to be monoclinic with space group P2₁/a. The unit cell dimensions are: a = 10.42(2), b = 10.16(2), c = 7.36(1) Å, β = 91.1°, Z = 4 and cell volume = 779.04 ų. The seven strongest lines in the powder diffraction pattern are (d,I,hkl): 7.30 (45)(110), 3.23 (80)(130), 3.04 (75)(2¯02), 2.98 (85)(202), 2.88 (70)(320,212), 2.84 (100)(230), 1.702 (40)(522). It is colourless, lustre vitreous, no cleavage and VHN₅₀ = 725–783 kg mm⁻² with H ∼ 6. Calculated density = 3.48 g cm⁻³ which is very close to 3.46 measured density of a synthetic Ca₃ZrSi₂O₉. It is optically biaxial, positive, 2 V ∼ 72°, dispersion indiscernible. The cathodoluminescence colour is dull grey with a greenish tint. Refractive indices: α= 1.652, β = 1.658, γ = 1.670. The crystal habit is stumpy prismatic and a contact twin with b as twinning axis is observed. Optic orientation: α = c, β//b, γ = a.