Study on Gemmological Characteristic and Genesis of Blue Pyrophyllite-type Corundum from Qingtian, Zhejiang Province

The blue pyrophyllite-type corundum of Qingtian is originated from the rhyolitic tuff, and microcrystal, branch-like crystal and monocrystal are the main crystal forms of this kind of corundum. By X-ray powder diffraction analysis, electron microprobe, infrared absorption spectrum, Laser Raman spectrum and differential thermal analysis et al, we can see that the chemical compositions of the corundum are rich in silicon while free of iron, and the impurities of titanium and iron lead to the colour of this corundum crystal .The recent experiment has confirmed that the blue pyrophyllite-type corundum may be transformed by metamorphism under the condition of the acid and medium-high temperature.