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

Over the past few years, numerous Verneuil-type (flame fusion) synthetic sapphires and rubies w i t h somewhat natural-appearing induced fingerprint in-clusions have surfaced i n the trade. This article reports the results of a series of experiments conducted t o explain the phenomenon of induced fingerprints and h o w they are produced i n gemstones generally and i n flame-fusion synthetic corundum specifically.

corundum, sapphire, treatments.6, synthetic corundum.7, synthetic sapphire, inclusions.5, gems

Gübelin examines the identification of newly introduced Chatham flux-grown blue and orange synthetic sapphires and of natural sapphires whose color has been altered by heat treatment or surface diffusion. The physical properties of the Chatham synthetics differ little from those of natural sapphire, making microscopic examination particularly important. Blue Chatham sapphires may show irregular blue, yellow, and colorless zoning, straight or angular growth structures, polysynthetic twinning, coarse or delicate flux residues forming feathers, veils, nets, lace-like patterns, and misleading “fingerprints,” together with black platinum platelets, rods, splinters, and needles that reflect with a characteristic silvery metallic lustre; X-ray analysis confirmed the metallic inclusions as platinum. Some blue specimens also fluoresce intense pale green under long-wave ultraviolet radiation. Chatham orange sapphires range from brownish orange through orange-red to pinkish-orange “padparadschah” colors and likewise contain flux residues and platinum inclusions that provide important evidence of synthetic origin; ultraviolet absorption and electron-spin-resonance measurements are also investigated as possible means of separation from natural stones. Gübelin then discusses heat-treated natural sapphires, in which high temperatures may produce pockmarked surfaces, altered or melted mineral inclusions, circular tension fractures with lace-like rims, enhanced cloudy or phantom-like zoning, and fine exsolved particles producing turbidity. Diffusion-treated sapphires may additionally show strongly colored surface-reaching fissures and inclusions, irregular surface coloration, and concentrations of color along facet junctions and the girdle; immersion in a highly refractive liquid makes these features particularly conspicuous. Gübelin emphasizes that no single characteristic is universally diagnostic and recommends careful comparison of macroscopic appearance, physical properties, ultraviolet response, spectra, and especially microscopic inclusions when distinguishing natural, synthetic, heat-treated, and diffusion-treated sapphires.

gems, inclusions, beryl, emerald, Madagascar

Emeralds from a new deposit in Madagascar are described. The emeralds originating from a mica schist in the south-east of the island are sim ilar to Zambian emeralds, mainly as to their blue-green colour and optical constants. However, mlnor chemlcal dlfferences and the observation of incluslons may allow a dlstinction. The worklng of thls new deposit is at present sporadlcal and carrled out wlth only simple technical means.

corundum, inclusions.5, ruby, spinel, beryl, emerald, Pakistan.12, Afghanistan.12, chemistry.2, geology.11, gems, spinel inclusions

Only during the last few years have the gem riches of Pakistan become known to the rest of the world. This article reports on three gem materials currently being mined: emerald, corundum (most importantly, ruby), and spinel. Intensely colored emerald crystals occur in dolomitic talc schists in the Swat Valley. Unusually high optical properties and density serve to distinguish these emeralds from those found elsewhere. Numerous gas-liquid inclusions are also typical. In the Hunza Valley, specimen-and gem-quality crystals of corundum and spinel occur in beds of marble enclosed in gneisses and mica schists. The gemological properties of the Pakistan rubies and sapphires vary only slightly within normal limits.

corundum, Pakistan.12, beryl, emerald, gems

Gübelin describes the emerald deposits of the Swat Valley in northern Pakistan, the second part of his survey of Pakistan’s gemstone occurrences. He discusses the geological setting and occurrence of the emeralds and examines their gemological properties and characteristic internal features. The Swat emeralds occur in metamorphic rocks and are notable for their rich green color. Microscopic examination reveals characteristic mineral and fluid inclusions useful in distinguishing the material from emeralds of other sources. The article considers the quality and appearance of the emeralds as well as the nature of the deposits and their significance as a Pakistani gemstone resource.

corundum, ruby, sapphire, Sri Lanka.12, inclusions.5, gems

Sri Lanka, formerly Ceylon, remains one of the single most important sources for fine gemstones. Especially notable are blue sapphire, pink sapphire or ruby, and yellow sapphire; alexandrite and cat's-eye chrysoberyl; and almandite and hessonile garnet. Spinel, tourmaline, zircon, moonstone, and quartz are also relatively common; they share their country of origin with several rarer gemstones as well. Most of the gem-quality material is found in alluvial deposits throughout the island, which are mined by primitive methods. In many instances, the Sri Lankan origin of the gemstone can be determined by characteristic inclusions, several of which are also discussed in this article

corundum, ruby, sapphire, Thailand.12, Cambodia.12, inclusions.5, treatments.6, gems

With the recent drastic decline in production from the classic ruby mines of Burma, Thailand has become the world's major source of gem ruby. The majority of the ruby production, as well as some significant sapphire production, comes from the provinces of Chantliabuti and Ttat in southeastern Thailand. This article reviews the geology of these alluvial deposits and describes the wide range of methods used to mine the corundum. Gemologically, the Thai rubies are distinguished by their violet overtone, inhibited fluorescence, and characteristic inclusions. Also discussed is the heat treatment of corundum to enhance color, which has become a major industry in Clianthaburi. The newest product, golden" sapphire, is examined, including the apparent stability of the color produced and clues to the det ection of the heat treatment."

corundum, Pakistan.12, gems

Gübelin describes the ruby occurrence in the Hunza Valley of northern Pakistan, where ruby and red spinel occur in marble. He discusses the geology and mineral associations of the deposit and the gemological characteristics of the corundum. Inclusions identified in the rubies include calcite and pyrite, while apatite occurs in both ruby and spinel. Chemical analyses are compared with Burmese ruby; a Hunza ruby contained 0.81% chromium, compared with 1.30 and 1.81% in the Burmese specimens analyzed. The article is illustrated with geological maps and 22 color figures.

corundum, sapphire, treatments.6, synthetic corundum.7, synthetic sapphire, inclusions.5, gems

corundum, inclusions.5, Thailand.12, gems

Although the general principles of photomicrography are easily learned and applied, high-quality photomicrography is an art that is mastered only with time and great patience. The microscope must be kept scrupulously clean, and the effects of light on the subject inclusion must be fully understood in order to determine what method(s) of illumination will yield the most useful photographic image. Specialized techniques that can save film and time, while producing top-quality photomicrographs, are usually learned only through long hours of experience. This article discusses some of these techniques, such as the importance of a properly prepared microscope and photographic subject, as well as the control of vibrations and exposure time. In addition, the various methods of illumination that are adaptable to a standard binocular gemological microscope are introduced.