Study on the Chromogenic Mechanism of Blue Kyanite from Coronel Murta, Minas Gerais, Brazil

• Published in: Crystals (Basel) Vol. 15; no. 4; p. 302
• Main Authors: Chen, Xiaorui, Guo, Ying, Gao, Min
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.04.2025
• Subjects: Absorption spectra; Aluminum silicates; Chromaticity; chromogenic mechanism; CIE 1976 Lab uniform color space; Color; ED-XRF; Fourier transforms; Gems; Infrared spectrophotometers; Infrared spectroscopy; Iron; Kyanite; Light; Precious stones; Spectrum analysis; Titanium; Brazil; China; United States > US
• ISSN: 2073-4352; 2073-4352
• DOI: 10.3390/cryst15040302

This study explores the factors influencing the body color of kyanites and the chromogenic mechanism from a novel perspective of gemstone chromaticity. The gemological properties of 20 samples from Coronel Murta, Minas Gerais, Brazil, were characterized using a color spectrophotometer, Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV–Vis). The results indicate that the Fe content in kyanites significantly affects the hue angle h°, chroma C*, and colorimetric coordinate b*, with higher Fe concentrations resulting in a deeper blue hue. Additionally, the Cr and Ti contents influence the body color of kyanites. As the Ti content increases, the lightness L* of kyanites decreases. In the UV–Vis spectrum, the lightness L* of natural samples is significantly related to the wavelength corresponding to the first peak in the orange-red region, and the absorption band at 600 nm also influences the hue angle h°.