Gemmological and Mineralogical Characteristics of "Ivory Jade" from Tibet

The named "ivory jade" produced in Dingqing county of Tibet is a kind of magnesite jade, most of which is white, and some of which presents red colour in veins. This kind of jade is compact and suitable for carving. The gemmological and mineralogical characteristics of the "ivory jade" were studied with the help of conventional gemmological instruments, slice observation, scanning electron microscopy, infrared spectroscopy, Raman spectroscopy and X-ray powder diffraction. The results showed that the main mineral component of "ivory jade" is magnesite and the minor minerals are quartz and hematite. The size of magnesite particle is less than 4 microns which belongs to micrite. And the quartz is cryptocrystalline granular and cemented with magnesite matrix. Transparent quartz veins and red hematite veins are distributed in the magnesite fractures. According to the area where the magnesite jade was found, it is speculated that its formation is related to weathering-leaching react to ultrabasic.