Comparative Study Of Titanite And Heat Treated Titanite

As a more general species among rare gemstones,Titanite is be loved by the market for its diverse color,strong luster and intense fire.Nature Titanite contains 1-800 ppm radioactive element U,Th,which release ?-recoil nuclears that damage crystal structure and make Titanite amorphize gradually,thus affecting the color and transparency of Titanite.In order to better understand the influence of ?-irradiation damage on the properties of Titanite and the improvement effect of heat treatment on the properties of Titanite with different degrees of damage,lots of experiments are carried out,such as conventional gemmological test,micro magnification observation,XRF element analysis,Raman spectroscopy,and UV-Vis absorption spectroscopy.Four different color Titanite crystals are used as samples to discuss the influence of heat treatment on the color of Titanite.At the same time,some samples were treated at different temperatures or at the same temperature for different time.The main conclusions are as follows:The results show that the natural gem-grade Titanite can be divided into two major categories based on its color,chemical composition,absorption spectrum and other characteristics:(1)the dark-colored series(including dark brown,reddish brown maroon and orange red,etc.)has relatively higher content of U and Th,and tends to accumulate more lattice damage.The UV-Vis absorption spectrum shows a series of strong absorption lines and narrow absorption bands in red and near infrared regions,with complete absorption in the yellow region and below.Raman spectra show that the reddish-brown samples are seriously damaged and partially amorphized,characterized by the decrease of absorption peak intensity,the increase of FWHM and the appearance of intermediate structural characteristic peak.(2)The Light-colored series(including green,yellow,yellow-green and a small amount of light-dark brown and tea-brown Titanite)has relatively low U and Th contents and usually crystallizes well.Its absorption spectrum has a weak absorption broadband centered at 600 nm.The results of heat treatment show that the light-colored Titanite with slight irradiation damage can be repaired well after heat treatment at 600 ? for 16 h,and its color is obviously improved.As the temperature is further increased,the sample almost achieves complete crystallization.The color changes from orange-red and maroon to dark tea-brown,with significant decrease of beauty.The results of heat treatment are affected by the initial damage degree of nature samples.The lattice defects and the color of the dark samples are only slightly repaired and improved,even heating at 800 ? for 2 h.This is attributed to its partially amorphization.At the same time,over-long treatment time and improper heating/cooling rate will cause a large number of cracks in Titanite samples,which will affect the transparency and quality of Titanite.Therefore,lots of attention should be paid during heat treatment.