Study On Color Mechanism And Radiation Of Zircon From Changle, Shandong Province

The occurrence features of the zircon from Changle,Shandong Province, areintroduced in short on the basis of the spot investigation of the author and theprevious work of other researchers. The physical properties, the internal and externalfeatures, and the chemical compositions are studied by using conventionalgemological methods、 X-ray fluorescence analyse （XRF）、 LA-ICP-MS andelectron microscope. The spectroscopic characteristics and metamict degree arediscussed by using LA-Raman spectra and IR absorption spectra. A series ofheat-treatment experiments of zircons had been finished at different temperature inoxidizing and reducing atmosphere. The colors and their variations were studied byUV_NIR spectrometer. The formation mechanism of the zircon colors were discussedon the basis of the experiments. Using LA-ICP-MS and HPGe gamma spectrometer,the U-Pb radioactive ages, radioactive elements and specific radioactivity werestudied.The results show that the zircon generally has good transparency and it is biggrain （11×7×4mm～2×3×2mm） with brown of different shades, dark brown indominant. The main chemical compositions are ZrO₂and SiO₂. The trace elementsare composed of impurity elements which are mainly Fe、Ti、P、Sc and so on,radioactive elements such as U and Th， and rare earth elements. REEs arecharacterized by yttrium group and rich in HREEs. Pronounced positive Ceanomalies and slightly negligible Eu anomalies suggest crystallization from relativelyoxidized conditions. LA-Raman spectra and IR absorption spectra both show that thesamples are typically the high-type zircon. All the features above hold that the zirconfrom Changle is a gem source because of its value in use.The fact is found that the color of the zircons after heat-treatment changed to thecolorless，yellow or orange in oxidizing atmosphere and colorless in reducingatmosphere. All the samples begin to fade significantly at400℃. The results showthat the red and redish brown colors of zircons are attributed to the color center and Fe3+is responsible for the yellow coloration of zircons. Only a low temperature canmake zircon change to perfect colorless, and hence the color enhancement of zirconhas tremendous commercial value.The U-Pb age of zircon from Changle is18.30±0.45Ma, which is interpreted asthe crystallization age, and the main radioactive elements are U and Th. Thejewellery with zircons from Changle are safety to wear for consumers because itsspecific radioactivity is far lower than exemption level from Regulations for radiationprotection （GB8703-88）.