Trigonal system, arh = 0.553nm, α = 54 ° 49 '; Z = 2. O […]
Trigonal system, arh = 0.553nm, α = 54 ° 49 '; Z = 2. Or ah = 0.509nm, ch = 1.407nm; Z = 6. It can be regarded as a derivative structure of corundum structure. The difference is that the position of Al3 + in corundum is replaced by Fe2 + and Ti4 + and arranged alternately, resulting in the disappearance of the c-slip surface, changing the space group from R3c to R3.
At high temperature, Fe and Ti in ilmenite are disorderly distributed and have a hematite structure (ie, corundum structure), so a FeTiO3-Fe2O3 solid solution is formed, and its composition can be expressed as Fe3O2-xFe2xTi4xO3 (x represents the mole of ilmenite fraction). The temperature at which the space group transitions from R3c to R3 ranges from 1100 ° C (x = 0.65) to 600 ° C (x = 0.45). When 0.6> x≥0.5, a completely ordered space group R3 cannot be obtained; when x = 0.5, R3c to R3 transforms into a metastable state, and the solid solution begins to partially dissolve. Rhombohedral crystals. It is often irregular grain, scale or thick plate. Above 950 ° C, ilmenite and hematite form a completely homogenous homology. When the temperature is lowered, melting occurs, so ilmenite often contains small scale-like hematite inclusions. The color of ilmenite is iron black or steel gray. The streaks are steel gray or black. The hematite-containing inclusions are brown or brownish red streaks. Metal-semi-metallic luster. Not transparent, no cleavage. Hardness 5 ～ 6.5, specific gravity 4 ～ 5. Weak magnetic. Ilmenite mainly appears in ultrabasic rocks, basic rocks, alkaline rocks, acid rocks and metamorphic rocks. In the Panzhihua vanadium-titanium magnetite deposit in China, ilmenite is distributed in granular or flake form between titanomagnetite and other mineral particles, or oriented lamellae along the split surface of titanomagnetite.