corundum, ruby, Malawi.12, inclusions.5, gems

Describes gem-quality red and orange corundum from Malawi, material that became available in 1988 from deposits that had produced corundum since the late 1950s. The stones range from pale to dark red, with some material of fine facetable quality. Gemological examination shows variations in refractive index, birefringence and specific gravity related principally to differing chromium and iron contents. Microscopic features include growth structures with hexagonal symmetry, color zoning along growth planes, and mineral inclusions. The study characterizes the Malawi material and documents the relationship between trace-element composition, color and physical properties. A more extensive English-language study of the material subsequently appeared in The Journal of Gemmology in 1990.

Twinning, Natural Sapphire, corundum, inclusions.5, chemistry.2, gems

gems, treatments, heat treatment, inclusions, quartz, citrine, amethyst, goethite, hematite

Important article that details how goethite inclusions, are altered to hematite by heat treatment of amethyst to citrine. This note describes the conversion of goethite to hematite when amethyst containing goethite inclusions is heated to produce brownish yellow coloured “fired” citrine quartz. The resulting hematite pseudomorphs after goethite are always accompanied by at least some fracturing in the amethyst-citrine because of water loss during dehydration of the inclusions.

corundum, sapphire, Nigeria.12, inclusions.5, geology.11, gems

gems, corundum, synthetic corundum.7, flux ruby

Single crystals of corundum were grown by seeded techniques, such as stationary, seed-rotation, and top-seeded, from molten Na- or Li-cryolite (Na₃AlF₆ or Li₃AlF₆) flux. Inclusions—such as flux inclusions, negative crystals, and cavities—present in the crystals were examined under an optical microscope, and the formation mechanisms and shapes of these inclusions, depending on differences in growth technique and conditions, are briefly described.

corundum, color.4, inclusions.5, treatments.6, synthetic corundum.7, gems

Some minerals, such as rutile, hematite and ilmenite, found as inclusions in sapphires are capable of imparting body—colour to their host during high temperature heat treatment. The inclusions are cannibalized by the host sapphire for the chromophoric elements they contain. If the inclusions are not completely consumed by their host this ‘internal diffusion’ results in a zone of intensely coloured sapphire surrounding the remaining inclusions.

amber, inclusions, gems

Gübelin and Koivula examine the diverse inclusions found in amber, extending attention beyond the familiar plant and animal remains to the less frequently discussed inorganic and fluid features. The article illustrates insects and other organic inclusions together with gas bubbles, liquid-bearing cavities and other structures preserved in fossil resin. Particular attention is given to the processes by which inclusions became trapped and subsequently preserved and to microscopic features that provide information about the history of the resin. Examples include cavities interpreted as gas or air bubbles and two-phase inclusions possibly representing droplets of water with contraction bubbles. The text corresponds closely to the amber section of the authors’ 1986 Photoatlas of Inclusions in Gemstones, although some of the photographs differ.

corundum, inclusions.5, treatments.12, synthetic corundum.7, ruby, sapphire, Australia.12, Burma.12, Cambodia.12, China.12, Colombia.12, Greenland.12, India.12, Kashmir.12, Kenya.12, Malawi.12, Pakistan.12, Sri Lanka.12, Tanzania.12, Thailand.12, USA.12, Montana.12, spinel, gems

Sinkankas: A truly remarkable work and one of the major achievements in gemological literature of this century, affording as it does both a vast treasury of outstanding colored photographs of inclusions and remarks on same which explain their origin and significance. Such explanatory remarks appear in part one, and are followed in part two by succinct descriptions of geneses with contributions by Roedder, Meyer, and Stalder. Part three now treats inclusions themselves, ranging from amphibole to zircon, and also inclusions of glass, fluids, multiple inclusions, aggregates, and others of remarkable form or nature. Part four, the major part, treats the individual gem materials that host inclusions from amber to zoisite, and including phenomenal gemstones and rare species. Part five describes inclusions in man-made materials, mineralic, plastic, glass, etc. The references cited and general literature are by no means exhaustive and some major contributions by such as David Brewster and Isaac Lea are unaccountably absent.

gems, corundum, treatments.6, inclusions.5, Sri Lanka.12

The question of how to identify natural-colored from heat-treated corundum has long puzzled the gemological community. One important clue is now provided b y carbon dioxide fluid inclusions. Because such inclusions cannot survive heat treatment, their existence intact and unruptured in rubies and sapphires i s conclusive proof that n o heat treatment has occurred.

natural ruby, synthetic corundum.7, gemology, inclusions.5, gems

Schmetzer presents a comprehensive study of the identification and separation of natural and synthetic rubies, based on examination of approximately 900 natural and 350 synthetic stones. After reviewing the mineralogy and crystallography of corundum, he describes five principal methods of synthetic ruby growth and the analytical techniques employed, including microscopy, UV-visible and infrared spectroscopy, ultraviolet fluorescence, goniometry and chemical analysis. The principal emphasis is on microscopic inclusions and internal growth structures: rutile, boehmite, twinning and characteristic growth features are discussed as evidence of natural origin, while diagnostic inclusions and structures in synthetic material are related to particular growth processes and manufacturers. Natural rubies from 15 localities are described and compared, followed by similarly organized accounts of 11 types of synthetic ruby. The work is extensively illustrated and intended as a practical reference for determining whether a ruby is natural or synthetic and, in many cases, establishing its geographic source or method of synthesis.