Study on the Color-Influencing Factors of Blue Iolite

Abstract

This article explores the factors that influence the color of blue iolite, which is the gem-quality variety of the cordierite mineral. The X-Rite SP62 portable spectrophotometer was used to measure color in the CIELAB color space. ED-XRF and UV–vis were used for analysis. The results show that blue iolite contains the chromophore elements Fe and Mn, but the effect on the color of iolite is not significant due to the low Mn content. The lightness L* and the hue angle h° are mostly determined by its Fe content. UV–vis spectra show that iolite has a broad absorption band near 570 nm caused by the charge transfer between Fe2+ on the octahedron and Fe3+ on the T11 tetrahedron and results in the color of blue iolite. Each different standard light source has different degrees of influence on the color parameters of iolite, and the hue angle h° is the most influenced.

Literature Review – Analysis of sustainable business models in electric motorcycle rental

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Modeling the polychromism of oxide minerals: The case of alexandrite and cordierite

“…The cordierite, also called iolite in gemology, can be colorless or blue-violet depending on the crystallographic direction of the observation. [17][18][19] In this case, the origin of this effect is still a source of debate in the literature, but the most probable origin of the color is an Fe 2+ -Fe 3+ intervalence transition. 20 Thus, these two minerals are challenging systems to test embedding methods since they involve d-d localized transitions and d-d through space charge transfer transitions, respectively.…”

“…In alexandrite, the colors are due to d‐d transitions of the Cr 3+ dopant in the material, generating an absorption band in the visible part of the spectrum. The cordierite, also called iolite in gemology, can be colorless or blue‐violet depending on the crystallographic direction of the observation 17–19 . In this case, the origin of this effect is still a source of debate in the literature, but the most probable origin of the color is an Fe 2+ ‐Fe 3+ intervalence transition 20 .…”

Feasibility Study on Color Grading of Blue Iolite Based on GemDialogue Color Comparison Charts

“…It also coexists with aluminum-containing minerals, such as sillimanite and corundum [2]. Cordierite is used as a gemstone, which is known as "iolite" in the gem and jewelry industry [3]. Gem-grade iolite is mainly produced in Sri Lanka, Madagascar, the United States, Tanzania, Namibia, etc.…”

“…In order to better ensure the accuracy of color grading of colored gemstones, the CIE1976 L*a*b* uniform color space system was introduced and played an important role in the color quantization research of gemology. It mainly involves jadeite [14], peridot [15,16], iolite [3], amethyst [17], citrine [18], chromic garnet [19][20][21][22], tourmaline [23,24], sapphire [25], chrysoberyl [26], cubic zirconia [27], blue amber [28], and diamond [29].…”