Abstract: The blue jadeite,without any previous report,is recently appeared on the market of Guangdong Province.In order to identify the blue jadeite,the authors investigate sample with the conventional gemmological identification methods,such as infrared spectrometer(IR) and X-ray powder diffraction spectrometer(XRD).The results show that the main mineral component of this sample is jadeite and its content is 97.1%,so the sample is jadeite.To study its colouring mechanisms,the sample is tested with UV-Vis spectrum.The result shows that the main reason of showing the colour of blue is its absorption band,which is gradually enhanced after 480 nm at visible region.Chemical composition analysis by EPMA shows that blue of the sample is caused by vanadium ion.Based on the crystal field theory of both 3d transition-metal ions and jadeite,we can say that the transition metal ion——vanadium ion(V⁴⁺) caused the colour of blue because within the crystal the Al³⁺ is replaced by V⁴⁺ and this replacement is the cause of distorted octahedron.Therefore,blue is primitive colour caused by vanadium ion(V⁴⁺).