Yellow,Yellowish-green Prehnite Gemological Characteristic And Evaluation Of Prehnite

Fifty-one prehnites with totally different lightness,chroma and hue are selected,and the color X-Rite spectrophotometer is used to measure the color parameters of the samples.Based on CIE1976L*a*b*uniform color space,fifty-one prehnite samples color are quantified and analyzed to obtain their correlations.This paper will find out the internal and external factors that affects the prehnite color,and finally evaluate prehnite samples by color and put forward the quality grade.The color of prehnite is attributed to the charge transfer of O^2--Fe³⁺-OH and Fe³⁺-Fe²⁺by IR and UV-Vis spectra.The trace elements in prehnite were found to be iron and manganese by LA-ICP-MS.The increase of Fe leads to yellow hue,and the chroma increases first and then decreases.When the content of Fe is about25000ppm,the color degree reach maximum.The content of Mn is the decisive factor that makes the prehnite be yellow-green or yellow.The thickness of this cabochon and transparent stone is often different.To explore the influence of thickness,here cut three cuboids with different longth and width from one prehnite stone with uniform color and texture.Using X-Rite spectrophotometer,the color of prehnite samples are tested.It is found that the thickness of prehnite increases,and the lightness and chroma decreases.As for displaying and inlaying prehnites,the color can be influenced by the background.Here converts 9 kinds of non-colored backgrounds and 6 golden standard backgrounds to analyze variance of color.It is found that the bright colored background has a more significant effect on the lightness and chroma of prehnite?P<0.05?,while the hue effect is not significant.Prehnites with high lightness and chroma are more influenced by non-coloured background,and greenish prehnites hue change are more significant.Different light sources can also affect color.Converting three standard light sources D₆₅,A and CWF,the best display light source of yellow samples is CWF and green samples is D₆₅ respectively.The quality evaluation and classification of prehnite samples with different colors is carried out.When the yellow samples are divided into three grades,and the yellowish-green samples are divided into five grades,the classification result is the best.Here marks color centers and color stereoscopic of each grade,and obtains the range of different qualitative prehnites in the color stereo.