LA-ICP-MS Analysis And Mechanism Of Alexandrite Effect Of Sapphire From Fuping

Based on earlier studies made by scholars, this paperconcludes and summarizes the areal geological conditions、stratum characteristics、structural features、characteristics of ore rock of Fuping allochroicsapphire mining area in detail. Through visual study and polarizing microscope observation,surrounding rock, sillimanite biotite gneiss, of Fuping allochroicsapphire showslepidoblastic texture and typical gneissic structure.A variety of researches on the sapphire from Fuping are involved in this paper, by which the gemological features of the sapphire from Fuping can be interpreted and characterized. The results indicate that the sapphire from Fuping is good from the forming degree,filled with cleavages. The R.I. is higher than the R.I. Criterion of the corundum and the S.G. is lower than the R.I. Criterion of the corundum. The clarity is not good. By the LA-ICP-MS,there is the rutile in it.By LA-ICP-MS,compared with the sapphire from other areas of metamorphic rock and sapphire from Burma, we can see that the content of Fe and Ga is higher, the Ti is lower. Compared with the conclusion of Ahmadjan and Guo,J, the sapphire from Fuping obey the conclusion of Ahmadjan, but not with Guo,J. So the conclusion of the Guo, J , that Ga=100ppm can divide the sapphire from basalt rock and metamorphic rock , is not accurate.Chemical element ,as well as ultraviolet-visible light absorption spectrums are brought forward to account for the mechanism of alexandrite effect in sapphire from Fuping. It is the ions of Cr³⁺ and V³⁺and Fe that contribute mostly to the forming of alexandrite effect.The absorption peak of 375nm、386nm、450nm and 741nm is caused by Fe³⁺; Owing to the V³⁺andCr³⁺, there are two absorption bands of purple light and yellow light.Compared with other sapphires from Xinjiang、Burma and synthesized sapphire, we can see that the main ions causing color of synthesized sapphire is V³⁺, the second one is Cr³⁺.But in sapphires from Fuping and Burma the main one is Cr³⁺,the second one is V³⁺.Without V³⁺, Cr³⁺、Fe³⁺ and Ti4+ result in the color of sapphire from Xinjiang together.