Cultured Akoya pearls are produced from 1 .5mm to over 10 mm. Among them, pearls with a pearl size of less than 5 mm have been commonly called " Rindama "in the pearl industry. Occasionally, a unique material is one in which two or three beads accidentally adhere during aquaculture. These have been circulated as twins and triplets.In order to observe the inside of these pearls, we confirmed them by μ-CT (X-ray computed microtomography), so we will introduce them.On the other hand, it has been reported that freshwater-cultured pearls are mixed in what is called small-sized Akoya-cultured pearls, and an easy identification method is being sought. We will also briefly report on the current status and problems of these mother mussels.

In southsea pearls, there were something by which a phenomenon similar to crack in a pearl layer showed. But there were also a pearl which couldn’t be confired these with μ-CT..

We research this reason by magnification to surface and found out that it was coused by growth layer junction.

When exposed to ultraviolet light, unprocessed akoya pearls fluoresce yellow, but bleached akoya pearls expressed blue white fluorescence.

We characterized the difference of fluorescence color between unprocessed pearls and bleached these. Unprocessed pearls showed a fluorescence maximum at ultraviolet region. On the other hand bleached pearls showed a fluorescence maximum at visible region, especially blue wavelength range. Fluorescence spectroscopy can be utilized which akoya caltured pearls were processed or not.

The structural colors of pearls depend on periodic structures of aragonite crystal layers and conchiolin sheets. The transmission and reflection spectra of Akoya pearls are calculated using Maxwell’s equations. A visual simulator coded by OpenGL Shading Language is also developed which can visualize the structural colors of Akoya pearls using the calculated spectra.

In jewelry market of these days, we can often see the pearls sold as “Untoned” or “Natural Blue”, emphasizing not to be tinted and colour-treated.

On the other hand, colour-treated pearls with unusual colours such as “Lavender”, “Pistachio” and “Chocola” are sold, by which consumer’s choice was supposed to be expanded to enjoy inexperienced colours.

However, regarding to colour-treatment with dye, the effects obtained by the treatment may be unstable. The main factors for faded colour and decreased luster must be sweat, abrasion, light and heat. Especially, ultraviolet is a frequent high-risk factor faced always in daily life.

Then, I performed light resistance tests for various coloured pearls generally seen in the market to inspect the durability in pearl colours and change of appearance against Ultraviolet.

Nowadays pearls in the market are almost cultured pearls. Especially many of nearly round pearls are nucleated cultured pearls and the nacre thickness is an important quality factor. By Soft X-ray photograph, the internal structure and the nacre thickness can be examined. However, each of pearls formed by various kinds of mother oyster or mussel shows different size and possesses a different size of nucleus. Then I invested how the nacre thickness of various pearls should be graded. In addition,I consider the nacre thickness which is needed for as pearl in gem.

Fluorescence spectroscopy was measured to see the relavance between fluorescence and optical defects. In fluorescence spectroscopy, it is possible to display the fluorescence spectrum and excitation spectrum of a sample and their emission intensities in three dimensions. When the excitation spectrum of a specific fluorescence peak is measured, the one that matches the absorption spectrum can be obtained. The relationship between the fluorescence and the optical defects can be confirmed by the absorption peculiar to the defects.

A fascinating synthetic diamond is the size used for the engagement ring, and it was able to be obtained for tens of thousands of yen. It often found on the market in Japan. Its diamond would have been produced by the HPHT method (Fig.1). There is an identification report as follows. This is a laboratory grown Ⅱ type diamond, weight 0.49ct, color J (very light blue), clarity VS1, cut good, polish good, symmetry good and fluorescence none by International Gemological Institute (IGI). This diamond is produced by doping boron to make it colorless by blue, which is a complementary color of yellow. This diamond has several metal inclusions. This diamond is said to be imported via India.

In this report, we will introduce about gemological observations on large HPHT-grown synthetic diamond crystals made in China. Through careful observations, these products can be confidently identified as synthetic.

The diversity and similarities of double-terminated crystals represented by Herkimer Diamond will be introduced in this presentation. Focusing on the presence or absence of fluorescence and the morphology of the crystals, it will be used as basic data for future research. Afghanistan and Pakistani double-terminated crystals with fluorescent petroleum inclusions are widely distributed sold. These crystals occur as veins in limestone. Herkimer Diamond has been recognized for the existence of fluorescent inclusions since around 2010, and is sold with added value, although the quantity is small. Herkimer-like double-terminated quartz is rarely occurred in the colorless and transparent Arkansas quartz. It may be sold under the name of Arkimer Diamond to differentiate it from Herkimer Diamond. The double-terminated crystal with petroleum-like inclusions found in 2009 will be introduced. As an oil-containing inclusion crystal, we will introduce a specimen from Spain, which is a rare production area. In addition, although it does not show fluorescence, we will introduce Herkimer-like crystals from Yunnan, China, the Republic of Mali, and Argentina.

Itoigawa city in Niigata prefecture is a main locality of jadeite in Japan. However, unlike Myanmar, pink jadeite is not seen. Actually, there comes so-called “pink jade”. In this research we tested them and found they are zoisite and clinozoisite coloured by manganese.

We analyze some light-blue minerals that appear to be chrysocolla associated azurite and malachite. However, the results of EDS show that these light-blue minerals cotains a high concentration of Mg that should not be present in chrysocolla. Combining the experimental results of FTIR, Raman Spectra, and XRD, we believe that these minerals are actually talc.

The occurrence of the whitish internal zone in opal is observed at considerable frequency to precious opal which is in igneous rock origin. We analyzed it with observation by the thin section to investigate whitish zone cause. As a result, the outbreak of the whitish zone was found to cope for the increase of the alkaline component.

Fluorescence-enhanced Si photo-diode (FE-PD) composed of ruby and Si-PD was developed for UVC measurement. UVC light can be detected with high sensitivity by using ruby which emits red photoluminescence (PL) under UVC irradiation.

The sol-gel method for synthesizing silica glass from a liquid raw material is a simple experiment that can be carried out at room temperature without heating, and is easy to operate even in the relatively lower grades of a college of technology. When the silica glass synthesized in the experimental class conducted in 2019 was stored, there was a difference in the gel state between hydrochloric acid and acetic acid used as acid catalysts. This time, authors will describe these changes over time and the results of the experiments conducted in 2021.

We applied fluorescence fingerprint to various rubies, and analyzed by principal component analysis. Then, k-nearest neighbor algorithm was used to classify them to some groups. Our approach was found to be beneficial for preliminary geographic origin determination.

In recent years, Paraiba tourmaline from Qintos, Brazil, which has a low copper content, has been distributed. We analyzed Paraiba-tourmaline using LA-ICP-MS and studied the origin determination, especially for samples with low copper content.