A kind of unnamed Fe-Cr-Ni mineral was found in chromite of Luobusa ophiolite in Tibet. EPMA shows that its molecular formula is Ni0.45Cr0.29Fe0.26, and the powder X-ray diffraction data are shown as follows (inside the parentheses areI/Io,hkl): 2.060(100, 111), 1.775(70, 200), 1.261(60, 220), 1.076(50, 311), 1.027(50, 222). According to the powder diffraction data, the crystal structure of this alloy belongs to theγ-Fe kind of metal element. The authors determined the atom coordinate and calculated the theoretical powder diffraction pattern in term of the arrangement ways of the metal element. The calculations reveal that the theoretical powder diffraction pattern is basically consistent with the observable powder diffraction data. The crystallographic data of Fe-Cr-Ni alloy can be summed up as follows:a=3.562 2 ,space groupFm3m, the number of molecules in unit cellZ=4, Dc=8.212 g/cm3.