Single crystals of corundum containing a small amounts of various dopants (Cr^<3+>, Fe^<3+>, Ti^<4+>, La^<3+>, Nd^<3+>, Dy^<3+>, and Yb^<3+> oxides) were grown by the methods such as seeded (with or without lid) , seed rotation, top-seeded, and temperature alternating from a cryolite (Na_3 AlF_6) flux. Good crystals were obtained under the following conditions: growth temperature, 1050 ℃; temp. difference between baffle plate and seed crystal, about 0.5 ℃; temp, differ. (bottom-baffle) , less than 3 ℃; baffle aperture, 10〜15%; growth rate, less than 10 mg/hr; seed rotation, 30 rpm; dopant, 1〜3 wt% per flux weight. Crystal continuity from the seed to the new growth were achieved well using two steps temperature elevating method by which the surface of the seed crystal is dissolved slightly. Habit modifications of corundum crystals due to the kind of dopants were as follows : Cr_2O_3 or Fe_2O_3 doping, tabular crystals surrounded by the c (0001), r {1011^^-}, and n {2243^^-} planes; barrel-shaped crystals composed of the c (0001) and n {224^^-3} planes were synthesized by the TiO_2 dopant; using the rare earth dopants, hexagonal-prismatic crystals having the c and a {112^^-0} planes were obtained. Corundum crystals possessing the zonal structure which was caused by variation of the distribution coefficient were produced by the temperature alternaing method.

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Inclusions observed in an emerald cut stone from Muzo, Columbia were studied by means of microscopic observations and electron probe microanalyses. Physical properties of the stone are summarized in Table 1. Solid inclusions are identified to be pyrite, pyrrhotite, pentlandite and rutile, whose EPMA results are shown in Table 3. Their descriptions and mutual relations are described in some detail, with photomicrographs (Fig 5〜10). Two-phase or three phase inclusions are also observed, but they are much smaller in size than common emeralds from Columbia (Fig 11〜15). How to identify species of solid inclusions under the gemmological microscope is briefly described.

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Kokichi Mikimoto, after successfully produced half spherical pearls in 1893, continued all effort to produce spherical pearls, and eventually succeded in 1905. The first five pieces of spherical pearl were found in mother-of-pearls which were treated by Otokichi Kuwabara, who was originally a dentist, and later joined with Mikimoto. He used his skill of dentist to insert pearl nuclei wrapped by the outer epithelial cells of the mantle piece. He also developed many operating tools, and this is the reason why pearl-operating tools widely used in the present-day cultured pearl fishery resemble dentist tools. Another important person in the early days of Japanese pearl fishery is Tatsuhei Mise, who developed different technique from that of Kuwabara. Mise's technique is to transplant, using a specially designed injection needle, the outer epithelical cells of the mantle piece, together with nucleus, into the gonad or mantle tissue. Because of Mikimoto's ability as businessman and organizer, of development of two different new techniques of pearl operation, and of support from scientists in universities, Japanese cultured pearl fishery developed rapidly, and production increased tremendousely. The Japanese cultured pearls gradually received recognition from the world jewellers, and their market expanded world-wide. Mikimoto's ability as PR man played important role in this respect, and he opened cultured pearl jeweller shops not only in Japan, but also in London, Paris and New York by the 1910.

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Papers presented at the sessions on gems and gemmology, as well as papers relating gemmology presented at other sessions during the 10th IMA Meeting, held from August 16 to 26, 1976, in the University of Sydney, Sydney. Australia, are reviewed.

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The basic knowledge on the optical crystallograghy is introduced as a basis of investigation of gemstone. In this part, optical phenomena observed between crossed polars are mainly discussed. To explain the above phenonema, Poincare diagram was used, which is very convenient for representing vibrations of light wave. Although the observation of pleochroism is usually done with polarizer only or parallel polars, a much more delicate way is to use the dichroscope or Savart plate. It is shown that the determinations of extinction positions with respect to a definite crystallograghic direction sometimes give a knowledge on the orientation of the observed crystal plate.

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