Abstract:Beryl, Be 3 Al 2 (SiO 3 ) 6 , is a natural gemstone with many colors. Some of these colors can be induced or modified by exposure to ionizing radiation, by heating, and maybe by electrodiffusion. Small contents of chromophore chemical elements are related to the colors of beryl, like iron, chromium, vanadium, manganese, and others. There is great interest in relation to methods of improving or inducing colors in beryl. There is evidence that infrared spectroscopy (FTIR) can contribute to foresee beryl behavio… Show more
“…The peak at 800 cm −1 belongs to the symmetric stretching vibration peak of Si–O. 24,25 The infrared beam directed toward the crystal along the c -axis direction produced an infrared spectrum with only one peak at 800 cm −1 , while the spectrum obtained along the other directions showed an additional peak at 779 cm −1 , which reflected the directionality of the symmetric stretching vibration of the Si–O. 26,27…”
“…The peak at 800 cm −1 belongs to the symmetric stretching vibration peak of Si–O. 24,25 The infrared beam directed toward the crystal along the c -axis direction produced an infrared spectrum with only one peak at 800 cm −1 , while the spectrum obtained along the other directions showed an additional peak at 779 cm −1 , which reflected the directionality of the symmetric stretching vibration of the Si–O. 26,27…”
“…A yellow beryl can be heated and turned into a blue aquamarine. This practice is commonly applied in the jewellery and gemstone trade and influences the market value the stone has (Blak et al, 1982;Alkmim et al, 2017). It is rooted in the reduction of Fe 3+ to Fe 2+ ions (Blak et al, 1982;Alkmim et al, 2017).…”
Section: Blue To Yellow Coloursmentioning
confidence: 99%
“…This practice is commonly applied in the jewellery and gemstone trade and influences the market value the stone has (Blak et al, 1982;Alkmim et al, 2017). It is rooted in the reduction of Fe 3+ to Fe 2+ ions (Blak et al, 1982;Alkmim et al, 2017). Though this procedure yields a more desirable blue colour (Chankhantha et al, 2016), it can be reversed by irradiation with high energy, such as γ -rays (Alkmim et al, 2017).…”
Section: Blue To Yellow Coloursmentioning
confidence: 99%
“…It is rooted in the reduction of Fe 3+ to Fe 2+ ions (Blak et al, 1982;Alkmim et al, 2017). Though this procedure yields a more desirable blue colour (Chankhantha et al, 2016), it can be reversed by irradiation with high energy, such as γ -rays (Alkmim et al, 2017). This does not only hold true for the colour, but also for the spectral changes induced by heat treatment, which have been observed to be restored by irradiation (Goldman et al, 1978).…”
Abstract. Incorporation of ions into the crystal structure of beryl (Be3Al2[Si6O18]) can take place by direct ion-to-ion substitution of the framework components Al3+, Be2+ and Si4+ or by occupation of interstitial or structural channel sites. The most common impurities in beryl include transition metals, alkalis and H2O. It is accepted that the transition metals Mn, Cr and V directly substitute for Al at the octahedral site and induce colour. Similarly, the octahedral site can host Fe instead of Al. Nevertheless, it is shown that it remains disputed whether Fe can also be present at the tetrahedral, interstitial, or channel sites, and opposing hypotheses exist regarding these possibilities. However, in the case of Fe, not only the possible occupation of these sites remains under debate, but also their influence on the subsequent colour of beryl. Similarly, the residence of Li in the channels and at the Be tetrahedral or interstitial tetrahedral sites is still under debate. The presence of more than two types of H2O (type I and type II) in the structural channels of beryl is also unclear. This article aims to give an overview on the consensus and on the current debates found in the literature regarding these aspects. It mainly concentrates on the substitution by and the role of Fe ions and on channel occupancy by H2O.
“…Fe 2+ and Fe 3+ can exist in prehnite at the same time, and the relative content for Fe 2+ and Fe 3+ will also affect the color of the prehnite. In general, there are several mechanisms for heat treatment to change the color of gemstones, such as changing the valence state of coloring ions, 14 destroying the original color center of gemstones, 15 causing dehydration of some watery gemstones, 16 diffusing the coloring ions in the gemstone, 17 changing the lattice structure. 18 It remains to be explored whether the color of prehnite can be improved by changing the valence state of the chromic element Fe through heat treatment.…”
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