Spectroscopy and chromaticity characterization of yellow to light-blue iron-containing beryl

Abstract

The chemical composition and influencing factors of the colour of 95 yellow to light blue iron-bearing beryl are studied through Electron Microprobe Analysis (EMPA), Energy-dispersive X-ray fluorescence (ED-XRF) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectroscopy and X-Rite SP62 spectrophotometer. The intensities of the three characteristic hydroxyl stretching bands of the beryl from 3500 cm−1 to 3800 cm−1 prove they are low to medium levels of alkali bearing natural beryl. The wide absorption edge of 320 ~ 465 nm caused by the ultra-violet charge transfer from O2− to Fe3+ and the 650 nm absorption band in E//c-polarization caused by the intervalence charge transfer between Fe2+ and Fe3+ are the main factors affecting the colour of beryl. By applying CIE D65 standard light source and N9 Munsell neutral background as testing conditions, the colour parameters of 82 gem-quality beryl are tested. According to the results, iron-containing beryl colours are classified into yellow, yellowish-green, bluish-green, greenish-blue, and blue by the K-means cluster analysis method. The blue tone has a greater influence on the hue of beryl, while the yellow tone has a greater influence on the chroma. Iron content is higher in yellow and blue beryl. With the increase of iron content, the lightness of beryl decreased and the chroma increased.

Incorporation and substitution of ions and H2O in the structure of beryl

“…Yet, the figure also illustrates that while other green beryls (those which are neither coloured by Cr nor V) lack these Cr and V absorption bands entirely, their spectra represent a mixture of the spectral features seen in aquamarine and yellow beryl. According to earlier works, all of the yellow beryls presented here would be termed heliodor instead of golden beryl, as there is a strong Fe 2+ absorption visible in the E⊥c direction (Andersson, 2019;Shang et al, 2022). Furthermore, contrary to what was reported by Andersson (2019), no significant differences could be observed in the light blue and dark blue beryl spectra analysed.…”

“…This is, therefore, also referred to as ultraviolet charge transfer, UVCT (Fritsch and Rossman, 1988). However, in more recent studies, yellow beryls are further subdivided into heliodor and golden beryl on the basis of differing spectral features (Platonov et al, 2016;Andersson, 2019;Shang et al, 2022). Both shades of yellow colour are attributed to Fe 3+ , yet with the ions supposedly occupying different sites.…”

“…Both shades of yellow colour are attributed to Fe 3+ , yet with the ions supposedly occupying different sites. According to this classification, they substitute for Al in its octahedral position in heliodor, whereas in golden beryl the substitution takes place in the Be tetrahedron (Andersson, 2019;Shang et al, 2022). Moreover, Andersson (2019) suggests that heliodor does not contain sufficient amounts of ferric ion pairs that could result in IVCT and turn these yellow beryls into blue aquamarines upon heating.…”

An Improved YOLOv5-Based Underwater Object-Detection Framework

“…The autonomous and high-precision detection of marine organisms urgently needs to be realized. However, compared to land-based detection scenes [ 6 , 7 , 8 ], due to the harsh natural conditions of the seabed when collecting images, most of the images in existing underwater datasets are affected by color casts [ 9 , 10 , 11 , 12 , 13 ], low contrast [ 14 , 15 , 16 , 17 ], fuzziness [ 18 , 19 ], noise [ 20 , 21 ], and other quality problems, leading to the loss of clear contour features and partial texture information in the image, which may greatly reduce the usefulness of such images for target recognition. As such, the accuracy of target recognition will be greatly reduced when using such images for target recognition.…”

Study on the Chromogenic Mechanism of Violet-Red to Orange-Red Spinel

“…Chroma C* and hue angle h • can be calculated from color coordinates a*, b*. It has good color uniformity and is now mostly used in the study of gemstone chromaticity, such as beryl [15,16], peridot [17,18], turquoise [19,20], chrysoprase [21,22], jadeite [23,24], etc.…”