We obtained and examined melee-sized fancy color synthetic diamonds of various colours. They were obtained as CVD synthetic diamonds, but we found that they were mixed with HPHT and CVD synthetic diamonds and had undergone complex treatments such as irradiation and HPHT treatment.

Identification of HPHT annealed or artificially irradiated diamond color treatment is one of the challenging in the gem testing lab. To understand various optical centers in both fancy colored of natural diamond and irradiated diamond is the main key to separate the color origin of colored diamond. In this study, the experiment results of HPHT annealing, irradiation and coating colored diamond will be introduced.

Microphotographic images of rubies containing some inclusions were collected, and observed inclusions were classified to three groups according to their shape. Then YOLO v8 model was fine-tuned by the images labeled inclusions to detect inclusions and classify them to the groups automatically. The fine-tuned model correctly detected and classified about 65% accuracy.

Bicolor Fe doped MgAl₂O₄ crystals have been grown using floating zone (FZ) technique by changing O₂ gas concentration during growth process. Crystals in various colors were grown from various Fe concentrations and compositions (x=MgO/Al₂O₃ molar ratio) under various O₂ concentrations.

Color changes of ametrine and citrine after heating and gamma irradiation were investigated by spectroscopic observations.

Several localities in Japan are known as the occurrence of corundum although most of them are not gem-quality. Alluvial sapphires from Takeda River at Anamushi town, Nara prefecture, are well known by collectors as one of production areas for corundum because they show deep intense blue to purple color and good transparency. They, however, are quite small and not cuttable size, thus they have not been mined commercially. Due to the size, their gemological features are not clear. In this study, several alluvial sapphire samples were tested with FTIR, UV-Vis and Raman spectrometers and LA-ICP-MS to clarify gemological characteristics. Anamushi sapphires have been interpreted to be derived from metamorphic rock xenoliths within garnet-bearing andesitic rocks that forming Mt. Nijo. The sapphires show metamorphic features based on UV-Vis spectra and chemistry, however the presence of melt inclusions is not consistent with metamorphic origin. Yogo sapphires show similar features to Anamushi sapphires, thus the origin of Anamushi alluvial sapphire is possibly similar geological processes to Yogo sapphire.

Light blue zoisite fragments mixed in a parcel of blue sapphires reportedly from Aksum, Ethiopia were analyzed with LA-ICP-MS for U–Pb geochronological study and compared with the results on tanzanite samples collected in Merelani, Tanzania. Merelani samples provide an age of 555.2 ±5.7 | 8.1 Ma (n=37/45; MSWD=1.9). Aksum samples are isotopically indistinguishable from Merelani in terms of U–Pb isotope data. This result indicates the potential mixture with Tanzanian zoisites in the gemstone trade if zoisite deposits that is similar age as Merelani does not exist in northern Ethiopia.

There are many previous studies on the origin determination of emerald. This presentation introduces the methods of origin determination by CGL and the newly identified problems – e. g. determining Colombian emeralds from similar ones; different characteristics of Brazilian emeralds in the past and present.

β-quartz, alkaline feldspar and plagioclase crystals occur Kobana formation from Nakagawa town, Tochigi Pref. Japan. β-quartz is transformed to α-quartz, but crystal habit shows β-quartz. Alkaline feldspar belongs to monoclinic system and contains Or74 in mean composition, plagioclase contains An43 respectively.

The gemmological property of green jade from Guatemala was mostly categorized as omphacite by chemical composition with EDX. Most of them show the omphacite type reflectance FT-IR but some of them still show the jadeite type feature. In UV-Vis spectra, the Guatemala omphacite jade show weak absorption at 437nm but which is not so strong as jadeite line in Burmese ones.

This study discusses the differences in optical properties between pearls and plastic balls. Pearls exhibit high reflectivity due to their complex layers, which create their characteristic luster and iridescence. An experiment confirms that pearls reflect more light than plastic balls. This higher reflectivity explains the beauty of pearls. A computer simulation is performed to reproduce their appearance based on the intensity of reflection.

Abalone cultured half-shaped pearls from Onagawa, Miyagi Prefecture, have been distributed in the jewelry and pearl industry market since the 1960s. The appearance of the pearls is attractive not only because of their color but also because of their dome shape. When we inquired at the Onagawa Town Hall about the current status of abalone-cultured half-pearls from Onagawa, we were told that pearl cultivation is no longer practiced in Onagawa.

In addition, almost no records of pearl cultivation remain due to the Great East Japan Earthquake of 2011. The only record of pearl cultivation in Onagawa Town is a brief history of the cultivation of half-shaped pearls by abalone by the producer, Mr. Komatsu, in the "Onagawa Town Magazine". In this article, we will introduce Onagawa's abalone-cultured semi-pearls, which have become a legend, and briefly report on the structural differences between abalone, which belongs to the coiled shell family, and pearls produced by bivalves.

One of the most important quality elements of cultured pearls is the thickness of nacreous layer so-called “nacre thickness value”.

In 2022, we suggested “nacre volume ratio” based on the measurement results of 1500 loose pearls for a new evaluation index of “nacre thickness” of nucleated cultured pearls.

In this paper, we examine the evaluation of “nacre thickness” by measuring the Akoya peal necklaces around 6-9mm in diameter, which are the most commonly distributed as pearl products on the market.

116 years have been passed since the spherical Akoya peal was cultured for the first time in 1907. Today, the culturing techniques have spread all over the world and various types of cultured pearls have been produced. The production of Akoya cultured pearls started from Japan and now extended to China, Vietnam, the UAE and so on. In this paper, we report the inspection of Akoya cultured pearls from Halong Bay, Vietnam with comparing them to Japanese ones.

When trace elements contained in various pearls were measured, the element content differed even for the same type of pearl. We also examined the effects of substances present under mother-of-pearl during X-ray fluorescence.

Recently, dark-colored pearls have also been processed. his time, we bleached dark-colored pearls. And we observed and analyzed the changes about these pearls.