Figure 4
From: Spectroscopy and chromaticity characterization of yellow to light-blue iron-containing beryl
Colour classification of beryl applying CIE D65 standard light source and N9 Munsell background. (a) According to the result of K-means clustering, the colours of the 82 beryl samples can be divided into five groups. (b) The five groups of beryl colour: yellow, yellowish green, bluish green, greenish blue and blue.
