Factors controlling the morphology of crystals are analysed based on the concept of solid-liquid interface roughness. Mutual relations among dendritic, hopper and polyhedral morphologies of crystals are explained on the basis of growth rate vs. supersaturation relations. There are two transitional supersaturations σ^*and σ^**. Above σ^** dendritic morphology is expected, whereas below σ^* polyhedral crystals bounded by flat faces occur. Between σ^* and σ^**, hopper morphology is expected.Factors controlling the morphology of polyhedral crystals (crystal habit) are analysed, in relation to the factors controlling the morphology of growth spirals, which are related to the roughness of growth steps. It is suggested that the major factors affecting the morphology of polyhedral crystals are phases, solvents, growt temperatures, supersaturations, impurities. It is also suggested that the changes in size of growth unit may drastically modify the morphology of growing crystals.

抄録全体を表示

Laser beam scattering tomography was developed by a scanning ul-tra-microscope and applied to characterize crystal defects in transparent crystals. The optical inhomogenities caused by dislocation lines, stacking faults and aggregation of impurities are dected by the light scattering tomography, because the ultra-microscopy acts as a sort of phase contrast microscopy. The light scatterers are descriminated by shape and contrast of images and their angular dependences against crystallographic axes of the specimens.

抄録全体を表示

It was found for the first time that single crystals of MgTiO₃ solidsolutions showed chatoyancy and they could be used as a new modified cat's eye gem stone. The crystal growth experiment was made by the traveling solvent float zone method using a halogen lamp image furnace. The grown crystals tended to grow mostly along the [1010]-axis. As grown boules were darkend. but became transparent and colourless after annealing at 1300°C for 24 hours in oxygen atmosphere and showed distinct chatoyancy along the (0001)-plane.

抄録全体を表示

This is a review of color of pearls. It is evident on the base of studies that the color of pearls is the sum of iridescence and body color. The iridescence occurs by the interference of light reflected from the superficial and internal laminar structure of nacre, which is made of the accumulation of crystal layer and thinner organic sheet parallel to the surface of pearls. The crystal layer is from 0.3 to 0.8 μm thick and consists of a definite aggregate of many small tabular crystals of aragonite in a row. On the other hand, the body color is due to the absorption of light by pigment, nacreous matter and other matters.

抄録全体を表示

As a general rule, the gemstones in the ordinary jewelry trade are judged by the technique with unaided eye, and the so-called 'basic judg-ing method' based on the gemmology. Most gemstones can be judged by such a technique on the judging method. However, gemmologists sometimes encounter such gemstones which is not easy to judge. In recent years, because of technical process in making synthetic or man-made stones and diversification of making such stones, we meet more often than ever before such cases where we find it extremely difficult to distinguish between natural stones and imitations. Therefore, the introduction of new instruments and testing methods for the identification of gemstones in the jewelry trade was seriously discussed. Already some new analyzing techniques, using, for instance, flourescent X-ray, ultra violet, infrared and visible ray, are being employed by some gemologists. However, these new instruments are unfortunately too expensive to come into general use and are not as effective as one expected. In spite of these difficulties, the gemologists should promote utilization of new instruments since these methods are particularly useful in identi-fing some gemstones. It is the most important in the jewelry trade to become proficient in gemtesting with unaided eye and the simple methods based on gemmology. It may be said that the development of these technique and the basic instrumentation are the most important things we have to learn in the trade today.

抄録全体を表示

Gemmological properties and keys for identification of new natural gemstones, which have been discovered or appeared in the gem market from 1945 are described briefly, together with their histories of discovery. The minerals described are brazilianite, taaffeite, sinhalite, amblygonite, greened amethyst, ekanite, painite, tugtupite, trapiche emerald, jade-albite, grossular garnet, blue zoisite, red tourmaline, jeremejevite, transparent sodalite, bixbite, treated blue beryl, herderite, prosopite, ceruleite, charoite, transparent rhodochrosite, palygorskite, taprobanite, ammolite and sugilite.

抄録全体を表示

Coloured crystals of quartz of gemstone-grade, citrine, amethyst and blue quartz, have been synthesized under hydrothermal conditions ranging 320-330°C and 1000-1500kg/cm². Conditions for colourations were Fe impurity, K₂CO₃ mineralizer, Ag-lined autoclave for citrine and amethyst, and Co and Al impurities, NaOH mineralizer for blue quartz. These impurities were added in the forms of metals or metallic oxides. Gamma irradiation was necessary for the final colouration of amethyst. Infrared examinations of natural and synthetic quartz crystals were made in the spectral range 2000-4000 cm^-1.

抄録全体を表示