Colouration Mechanism And Positions Of Impurities In Yellow Beryl From Wulateqianqi, Inner Mongolia

On the basis of previous studies on beryl, LA-ICP-MS, X-ray diffraction analysi, infared spectra, electron paramagnetic resonance （EPR） spectra, UV-VIS spectra of the yellow beryls from Wulateqianqi, Inner Mongolia have been studied.LA-ICP-MS has been applied to analyze the chemical compositions of the yellow beryl. The result shows that there’s low content of alkali metal and a little Fe²⁺, Mg²⁺, Mn²⁺ in octahedral Al³⁺ site. The remaining ions are locattated in channel.The result of X-ray diffraction analysis show that the lattice parameters of yellow beryl from Inner Mongolia a is from 0.9208 nm to 0.9212 nm, c is 0.9195 nm from 0.9206 nm, the value c / a is about 0.999, greater than the theoretical value. The main isomorphic replacement is Be²⁺-Li⁺. There is a covariant relationship between lattice parameters and some chemical positions.There are vertical lines parallel to c axis and quadrilateral erosion on cylinders, round erosion on bottom. The refractive index no is1.570～1.575, ne is 1.560～1.568. The birefringence is 0.007⁰.010. The relative density is 2.5970～2.6366, which is affected by cracks and inclusions. There are growth and color ring in some samples. The infrared spectra of channel constituents in yellow beryls has been examined.There are two types of water molecules. Fe³⁺ in the channel produces band at 3234cm^-1. Na⁺ in the channel produces bands at 3159cm^-1, 3109cm^-1 and 3031 cm^-1. The EPR spectra shows there bands in 2.414, 1.999 and 1.711 （g）. These bands are attributed to both the presence of Fe³⁺ in substitution of A1³⁺ in the octahedral symmetry and Fe³⁺ in channel.There is no UV-VIS absorption bands which is associated to Fe³⁺ or Fe²⁺ at the octahedral site, so I infer that the yellow color may be caused by the [Fe2（OH）4]²⁺ in the channel sites.