Comparative Study on Gemological and Mineralogical Characteristics and Coloration Mechanism of Four Color Types of Fluorite

Abstract

Fluorite has been attracting the attention of gemstone mineralogists because of its rich color and excellent fluorescence properties. This paper studied fluorite with three color types (blue, green, and white) and five blue-purple fluorites with an alexandrite effect. Through the study of their structure, composition, and spectral characteristics, the gemological and mineralogical characteristics and coloration mechanisms of different color types of fluorites are compared and analyzed. The results show that the color of fluorite is caused by multiple color centers. Blue fluorite is associated with Y3+-F− color center, while green fluorite is associated with a Y3+-Ce2+-F− color center and Sm2+ color center, and white fluorite contains vacancy color center. The color of white fluorite is a mixture of yellow tones produced in visible light and blue fluorescence under UV light. Blue-purple color is caused by the colloid calcium color center and 2F− color center, and its changing from blue-purple to red-purplish (alexandrite effect) are due to colloidal calcium nanoparticles caused by radioactive element Th.

Analyzing Optical Properties of Natural Fluorite Crystals: A Comprehensive Investigation

“…Studies by Tsuda et al [18] elucidated that this Raman signal corresponds to the CaF 2 lattice vibration at 322 cm ¹. Russell [19] obtained Raman peak of uorite at 322 cm − 1 . Additionally, Liu et al [20] reported a Raman peak at 320 cm − 1 for white uorite. Lewandowski et al [21] observed Raman peak at 319.13 cm − 1 for calcium uoride.…”

“…Consequently, the PL emission peak of uorites from different areas under a short wave is mainly at 510 nm, and the intensity is weak [20]. The presence of the Yttrium (Y) element is considered one of the reasons why uorite exhibits uorescence [20], [36][37][38][39][40]. According to Table 2, the concentrations of Y in samples E, EB, FB, and G are recorded as 1.5, 0.6, 3.4, and 2 ppm, respectively.…”

“…Under the excitation of 260 nm, the PL emission peaks of samples E, EB, FB, and G are observed at 364 and 510 nm. Consequently, the PL emission peak of uorites from different areas under a short wave is mainly at 510 nm, and the intensity is weak [20]. The presence of the Yttrium (Y) element is considered one of the reasons why uorite exhibits uorescence [20], [36][37][38][39][40].…”

“…The study conducted by Liu et al [20] involved an investigation of the photoluminescence (PL) spectra of uorite at excitation wavelengths of 365 and 254 nm. The primary objective was to understand the factors contributing to the variation in PL emission.…”