apatite, Tanzania, gems

Gübelin and Schmetzer describe a new occurrence of cat’s-eye apatite from the Umba Valley, Tanzania, occurring in yellow, green and reddish-brown colors. A small proportion of the material is clear and transparent, but most specimens contain abundant fine, fibre-like inclusions and are therefore suitable for cabochon cutting. Properly oriented cabochons display a strong, sharply defined cat’s-eye effect. Examination of the inclusions showed that the chatoyancy is produced by numerous minute needles of goethite. The article illustrates the material with four color photographs.

diamond, inclusions, gems

Gübelin reports electron-microprobe analyses of mineral inclusions from nine diamonds. The inclusions were studied either after crushing the host diamond and separating the enclosed mineral, or by cutting and polishing the diamond until an inclusion was exposed at the surface; separated inclusions could also be examined by X-ray methods. The analytical results are presented for the various inclusion minerals, with discussion of their significance for the origin and formation of their diamond hosts. Of particular interest is the identification of a red inclusion as corundum (ruby), the first substantiated occurrence of ruby as an inclusion in natural diamond; this ruby is assigned to the eclogitic suite of diamond inclusions. The paper contains 17 figures, 16 in color, and two tables.

corundum, synthetic corundum.7, gems

Gübelin discusses the identification of newly available synthetic and treated blue sapphires, concentrating on Chatham flux-grown synthetic sapphire and on natural sapphires whose color has been modified by heat treatment or surface diffusion. He describes the crystal habits and physical and optical properties of rough and faceted Chatham material, followed by a detailed examination of diagnostic inclusions, some of which closely resemble inclusions in natural sapphire. Twenty-three color photomicrographs illustrate these features. A further 15 photomicrographs document characteristics of color-enhanced sapphires, including altered mineral inclusions surrounded by tension cracks, pockmarked girdle surfaces, pronounced color zoning, and concentrations of color in surface-reaching fractures.

garnet, Umba Valley, Tanzania, gems

Gübelin examines the internal features of garnets from Tanzania’s Umba Valley, a locality producing garnets across the pyrope–almandine–spessartine compositional range. The paper documents and illustrates their characteristic inclusions and considers their value for gemological identification and for interpreting the conditions under which the garnets formed. Later inclusion literature specifically records crystallographically oriented networks and star-like arrangements of rutile needles in Umba Valley garnets, citing Gübelin’s work on this material.

corundum, synthetic corundum.7, gems

Gübelin and Knischka describe a new gem-quality synthetic ruby produced by Paul O. Knischka using a proprietary “gradient technique” involving supersaturation and controlled cooling. The resulting crystals have an unusual nearly isometric or pseudocubic habit and exceptionally numerous well-developed, undamaged crystal faces, with examples possessing 32 or 38 faces. The authors compare several types of Knischka synthetic ruby with natural and Verneuil synthetic ruby, examining crystal morphology, trace-element chemistry, optical and gemological properties, fluorescence, and inclusions. In color and general appearance the material closely resembles natural ruby, although it tends toward a more violet red; refractive index, birefringence, and other standard properties offer little assistance in separation. Microscopic features include folded or feather-like inclusions, color zoning, two-phase inclusions, negative crystals, and occasional metallic platelets, some of which can resemble features in natural stones. The study emphasizes the increasing difficulty of distinguishing high-quality synthetic ruby from natural material and the potential diagnostic value of inclusions and trace-element composition.

tsavorite, grossular, Kenya, gems

Describes vanadium-bearing green grossular from the Lualenyi mine in Kenya’s Taita district, comparing its occurrence with material from Tanzania’s Lalatema Hills and Merelani, where grossular accompanies blue zoisite. The green colour is attributed to vanadium, with approximately 3% V₂O₃ reported. Internal features include probable byssolite inclusions and trails of minute liquid droplets.

beryl, emerald, Colombia, gems

Barriga Villalba and Barriga del Diestro present a monographic study of Colombian emerald, describing its principal characteristics and properties. The work considers emerald as a mineral and gemstone, with attention to its physical and optical properties, characteristic color and inclusions, and the features associated with Colombian material. It also discusses the geological occurrence and principal emerald-producing areas of Colombia, particularly the deposits of the Eastern Cordillera, and addresses aspects of mining and the evaluation of emeralds. The volume provides a contemporary Colombian account of the country’s most important gemstone and its distinguishing gemological and geological characteristics.

inclusions, gems

inclusions, gems

First comprehensive article on the determination of inclusions in gemstones by means of the electron microprobe. Techniques are described and results explained. Fine color illustrations. Essentially the same article appeared in Journal of Gemmology, 11(5), 1969, pp. 149–192, with 80 color photographs, 3 figures, and 49 references.

jade, jadeite, fei cui, nephrite, Wyoming, Burma, inlusions, gems