Cultured pearl technology, completed by the Japanese in the early 20th century, has drastically changed the size and appearance rate of pearls. It is now difficult to know the ecological facts of natural pearls. However, there is a survey report of the Mie Prefectural Fisheries Experimental Stations (Mieken Suisansikenjo) in Japan. In addition, pearl relics, such as the 8th century pearls of the Shosoin Treasure and pearls from Omura Bay during the Edo period, are preserved. They are thought to provide information on the size and appearance rate of natural Akoya pearls.

Analysis of this survey report and pearl relics shows that the size of natural Akoya pearls started at around 1 mm in diameter, and reached the 10-mm range on rare occasions. The standard size was in the range of 3 to 6-mm. Akoya pearls tended to have a higher appearance rate as they became smaller. This was because some Akoya pearl oysters contained several or dozens of seed pearls. According to the survey report, the number of Akoya seed pearls accounted for 97.5% of all pearls collected, and the appearance rate was 26.62% of the number of collected shells. On the other hand, the appearance rate of large Akoya pearls with a diameter of 4.7 mm or more was 0.015%, which means that 1.5 pieces of pearl appeared from 10,000 shells.

We have encountered a transparent bluish-purple cut stone that shows characteristics not found in the market of gemstones. The stone looks to be cordierite or scapolite, but its spectroscopic characteristics are different from either of them. The X-ray powder diffraction pattern was found to match with the data of Be-bearing cordierite (BeMg₂Al₂Si₆O₁₈) like mineral, which is a synthetic crystal. This mineral has not yet been described as a natural one in literatures, and would be a new mineral available for gem, if its locality is identified.

In 1962, Central Research Laboratory of Tokyo-Shibaura Electric Co. Ltd announced success in synthesizing diamond at HPHT conditions, which was the first announcement in Japan. This triggered preliminary action to develop original process of producing industrial diamond, and a special team was organized composed of members from Central Research Lab. and Toshiba-Tungaloy Co., Ltd. The team had to find new catalysts and to design a new apparatus that are different from those invented by General Electric Co. (GE), US, because GE had obtained several patents covering a wide range of conditions to synthesize diamond throughout in the world including Japan in 1959. A story introduced here is an effort and a way of the team, resulting in discovery of new catalysts and original design of an apparatus, which were basically different from those of GE, and their performance was tuned to be comparable with those of GE. Although their product did not appear in the market as a result, sum of their outputs are sufficiently meaningful in a view point of science and technology in the field, and might keep an interesting position in continuous progress of science and technology of diamond synthesis.

Optical properties of diamond are closely related to impurities, in which nitrogen is the most dominant. This article reviews researches on nitrogen impurities in diamond, focusing on their structures. Defects containing nitrogen atoms are named as IaA (A center), IaB (B center), Ib (C center), platelet, voidite and so on. A number of papers have reported models of the defect structures, although some of the models have not been definitely determined because of lack of direct evidence. Measurements of infrared absorption spectra are able to give concentrations of the nitrogen impurities in forms of the A, B and C centers.