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Small “Surprise” in Elbaite TourmalineRecently, a 0.86 ct orange-yellow elbaite tourmaline cabochon was submitted to Tai...
12/08/2022

Small “Surprise” in Elbaite Tourmaline
Recently, a 0.86 ct orange-yellow elbaite tourmaline cabochon was submitted to Taiwan Union Lab of Gem Research (TULAB) for identification service. The stone contained many prismatic and round xenocrysts. Among these inclusions were a prismatic crystal associated with a round crystals were observed near each other, a composition resembling an exclamation point (figure 1). The crystals were later confirmed to be diopside using Raman spectroscopy. Darkfield illumination, plane polarized light, and extended depth of field were adopted to obtain a clear microscopic image of this little “surprise” inside the gemstone.

Figure 2. The “exclamation point” inclusions were identified as diopside crystals using Raman spectroscopy. Photomicrograph by Shu-Hong Lin; field of view 4.11 mm.

Shu-Hong Lin
Institute of Earth Sciences, National Taiwan Ocean University
Taiwan Union Lab of Gem Research, Taipei
Tsung-Ying Yang, Kai-Yun Huang and Yu-Shan Chou
Taiwan Union Lab of Gem Research, Taipei

Gems & Gemology, Fall 2022, Vol. 58, No. 3, P. 364-365.

A Zircon with Strong Photochromic EffectRecently, a 6.54 ct oval faceted gemstone with greenish blue color (figure 1, le...
09/08/2022

A Zircon with Strong Photochromic Effect

Recently, a 6.54 ct oval faceted gemstone with greenish blue color (figure 1, left) was sent to Taiwan Union Lab of Gem Research (TULAB) for identification. The specific gravity of this stone was 4.68, and the refractive index was over the limit of the refractometer. Microscopic observation showed strong birefringence. In addition to standard gemological testing, Raman spectroscopy and comparison with the zircon reference spectrum R050203 from the RRUFF database (figure 2) confirmed it was a zircon. It was particularly worth noting that this zircon showed a significant color change from greenish blue to very dark yellowish green (figure 1) when exposed to a long-wave ultraviolet lamp.

To determine the extent of the color change and whether it was permanent or reversible, the zircon was first exposed to long-wave UV light for one minute and then under 10W white LED light for another minute (the light sources were placed approximately 3 cm away from the gemstone). After repeating this process several times with each exposure one minute longer than the previous time, we confirmed that the color changed from medium light greenish blue with strong saturation to a medium dark greenish yellow with lower saturation after two minutes of long-wave UV light exposure. However, the greenish yellow color gradually returned to the stable greenish blue color after photobleaching with LED white light for 30 minutes. Therefore, the stone was a photochromic zircon with reversible color change (as reported in N.D. Renfro, “Reversible color modification of blue zircon by long-wave ultraviolet radiation,” Fall 2016 G&G, pp. 246–251). After the color change reached its full extent under long-wave UV light, the zircon was analyzed by visible spectroscopy to record its continuous spectral change during the photobleaching process every six minutes (figure 3). The resulting spectra revealed that the light transmittance in the range between 450 nm and 550 nm gradually increased during the photobleaching process, and the greenish blue color finally returned to a stable state after 30 minutes.

Although this type of photochromic zircon has previously been reported, a zircon over 6 ct with such a significant photochromic effect is still rare and worth noting, especially since it exhibited a distinct difference in hue, tone, and saturation.

Figure 1. This 6.54 ct zircon showed a significant color change from medium light greenish blue (left) to very dark yellowish green (right) after exposure to long-wave UV for two minutes, and the color was reversible during the photobleaching process with LED white light. Photos by Kai-Yun Huang.
Figure 2. The stacked Raman spectra of the greenish blue zircon and a zircon reference spectrum from the RRUFF database; spectra are normalized and baseline-corrected.
Figure 3. Visible spectra of the zircon (after UV light exposure) during the photobleaching process were recorded every six minutes. The gradually decreasing spectral change implied that the color tended to stabilize.

ABOUT THE AUTHORS
Shu-Hong Lin is chief gemologist, and Yu-Shan Chou and Kai-Yun Huang are gemologists, at Taiwan Union Lab of Gem Research in Taipei.

://www.gia.edu/gems-gemology/summer-2022-gemnews-zircon-photochromic-effect

06/24/2022

Do not fall for a fake. This is how we test our incoming metals at Star Rapid. In this video Gordon demonstrates Spark OES gun & XRF (X Ray Flourescence) Gun...

06/24/2022

In this episode Star Rapid's CEO Gordon Styles discusses 3 of the most common methods of positive material identification (PMI) and RoHS testing for plastic ...

Fishbone Inclusion in a Burmese Peridot from MogokRecently, an 83.25 ct cushion faceted peridot with medium dark yellowi...
06/24/2022

Fishbone Inclusion in a Burmese Peridot from Mogok
Recently, an 83.25 ct cushion faceted peridot with medium dark yellowish green color and good clarity (figure 1) was sent to the Taiwan Union Lab of Gem Research (TULAB) for identification service. This peridot from Mogok, Myanmar, was relatively rare in the Taiwan market because of its impressive size, color, and clarity. Microscopic examination revealed a few short needle inclusions and a fishbone-shaped inclusion (figure 2), the latter of which is common in peridot from this origin. The backbone appeared to be a long-prismatic crystal with some vertical cleavage planes along it, while the smaller branches were composed of parallel tabular inclusions which might result from epitaxial exsolution. Due to peridot’s strong birefringence, bright-field illumination and plane polarized light were adopted to reduce the interference and obtain clear microscopic images.
Shu-Hong Lin
Institute of Earth Sciences, National Taiwan Ocean University
Taiwan Union Lab of Gem Research, Taipei
Figure 15. The fishbone-like inclusion in the Burmese peridot. Photomicrograph by Shu-Hong Lin; field of view 1.32 mm.

This article was published on Gems & Gemology, Spring 2022, Vol. 58, No. 1, p6
Please refer to the link below for the pdf file of the journal：
https://www.gia.edu/doc/spring-2022-gems-gemology.pdf
PS: The additional photo is a front view of the peridot

Tektite or obsidian? Natural glasses from Indonesia, Arizona, USA or Colombia.Photo/ Text by TULAB of GEM RESEARCH.In r...
06/24/2022

Tektite or obsidian? Natural glasses from Indonesia, Arizona, USA or Colombia.
Photo/ Text by TULAB of GEM RESEARCH.

In recent years, a lot of granular natural glass claimed to be "tektite" appeared on the market, which might be identified as "tektite" with certificates issued by the gem labs in China, Taiwan and Hong Kong. Most of the sellers use the trade names as Indonesian tektite, Saffordite, Colombian tektite or Mexican tektite. At the beginning, such objects were submitted to the TULAB for identification. Our gemologists confirmed that these objects were granular obsidian by various advanced instruments (FTIR, Micro-Raman, EDXRF, UV-Vis). However, some sellers still claimed that those natural glasses were tektite.

Therefore, about two years ago, TULAB started a series of tektite research, and successively collected obsidian samples from different origins and tektite samples from different origins, totaling more than 300 pieces of samples. After EDXRF analysis, traditional gemological testing, micro-Raman analysis, FTIR analysis, and UV-Vis analysis, it was finally concluded that the aforementioned "granular natural glass" were all obsidian, and a lot of obsidian from Indonesia in the market was claimed to come from Arizona or Colombia. At present, in Taiwan (or even in Asia), only TULAB may be able to test these obsidians and confirm their origin.

Inclusions were confirmed by Micro-Raman. (GR7-Dual Laser)

Figure 1. Australasian tektites from Thailand and granular natural glass (obsidian) from Indonesia, Arizona, and Colombia.
Figure 2. Swirly structure in the tektite from Thailand and crystal inclusions in granular natural glass (obsidian) from three other origins, including cystallites, plagioclase, biotite, apatite, and zircon.

This inclusion was found in an unheated spinel, which was confirmed to be an octahedral magnesite crystal surrounded by...
01/17/2022

This inclusion was found in an unheated spinel, which was confirmed to be an octahedral magnesite crystal surrounded by a spherical zoning that appeared to consist of tiny exsolved particles. The inclusions were confirmed by Micro-Raman.

Zircon halos are a common inclusion in corundum, and are often found in many gemstones. This is a zircon crystal includ...
01/11/2022

Zircon halos are a common inclusion in corundum, and are often found in many gemstones. This is a zircon crystal included in a faceted iolite with a rounded shape and surrounded halos consisting of small wings of fractures. Micrograph was taken with Gemscope GR7, and inclusions were confirmed with a Raman microscope.

A colorless Topaz of the customer was found to have some sub-metallic black to brownish red crystal inclusions, which we...
12/02/2021

A colorless Topaz of the customer was found to have some sub-metallic black to brownish red crystal inclusions, which were originally guessed to be rutile crystals, but were finally confirmed to be Tantalite ((Fe,Mn)Ta2O6) by micro-Raman. It is a common mineral in pegmatite, but a rare inclusion in gemstones.

This is an inclusion found in an aquamarine pear cabochon, with a flower-shaped pattern, which is actually a "hematite r...
10/04/2021

This is an inclusion found in an aquamarine pear cabochon, with a flower-shaped pattern, which is actually a "hematite rose" observed in the direction of the basal plane. Such shapes or forms composed of regular and symmetrical pattern are usually called fractals geometrically. This photomicrograph was taken with Gemscope GR7 with 5MP electronic eyepiece at 100X magnification, and the inclusion was confirmed by micro-Raman(GR7).

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