Qandilite, a new spinel end-member, Mg₂TiO₄, from the Qala-Dizeh region, NE Iraq

Abstract

Qandilite, a new species of the spinel group, has been found in a forsterite-rich rock in contact with a kaersutite-rich banded diorite from the Qala-Dizeh region, NE Iraq. Chemical analysis yielded MgO 29.62, FeO 10.32, MnO 0.76, Fe₂O₃ 28.27, Al₂O₃ 4.83, TiO₂ 26.41, SiO₂ 0.02, sum 100.23 wt. %. This analysis calculates to [(Mg_1.20Ti_0.60)][Mg_0.12Mn_0.02)(Al_0.17)]O₄ with a composition of Mg₂TiO₄ 63.8, MgFe₂O₄ 12.8, FeFe₂O₄ 23.4 mole %. Qandilite is cubic with a = 8.4033±0014 Å; cell volume 593.40 ų and space group Fd3m; Z = 8. The seven strongest lines in the X-ray diffraction pattern are (d,I,hkl): 2.971, 30, (220); 2.53, 100, (311); 2.101, 45, (400); 1.617, 50, (333, 511); 1.486, 60, (440); 1.0938, 30, (553, 731); 0.9704, 25, (555, 751). The colour is black, lustre metallic, streak black, fracture even and the cleavage perfect on (111). It is opaque, strongly magnetic, D_calc = 4.04, D_meas = 4.03, and VHN₁₀₀ = 960–1045 kg/mm², with H-7. The reflection colour is grey with a pinkish tint; it is isotopic with no internal reflections. Reflectance measurement data in air and oil in the range (400–700 nm) are given. Colour values for illuminant C in air and oil in terms of CIE colour space are: x = 0.307, 0.307; y = 0.311, 0.310; Y% = 13.10, 3.0; λd = 465, 460; and Pe% = 2.0, 2.2. Calculated data for the absorption coefficients (k) and refractive indices (n) in the range 400–700 nm are also presented.