jade, jadeite, fei cui, Burma, maw-sit-sit, gems

This article examines both the principles behind the functioning of the scanning electron microscope-energy dispersive spectrometer system and its application to the chemical and structural analyses of gems. The examples presented describe the distinction of natural from treated opals, the relationships observed between a diamond and its kimberlite matrix, the identification of inclusions in ruby and taaffeite, the elemental mapping and chemical analysis of maw-sit-sit,and the study of chemical interrelationships between various types of garnets.

tourmaline, cat’s eye, gems

corundum, inclusions.5, gems

The first substantiated identification of corundum (var. ruby) occurring as an inclusion in natural diamond is presented. The ruby is assigned to the eclogitic suite of inclusions in diamond, and the implications of its occurrence are discussed in relation to the genesis of “eclogitic” diamonds. It is concluded that diamond crystallizes from a melt over a long period of time with possible fluctuations in ambient temperature and geochemical environment.

corundum, Pakistan.12, gems

gems, jade, nephrite, diamond, tourmaline, sapphire

China’s gem resources are surveyed through their geological associations, mineral composition and traditional uses, with particular emphasis on diamond and the diverse ornamental materials historically grouped under the term yu. The introduction contrasts the country’s long history of carving and gemstone use with the comparatively recent development of organized gemmological research, exploration and synthetic crystal production. Gem occurrences are classified principally by their relationships to magmatism, pegmatites, contact metasomatism, metamorphism, hydrothermal alteration, surface processes and organic accumulation. Diamond-bearing kimberlites are described in terms of geological setting, intrusive form, texture, chemistry, associated minerals and xenoliths. Comparisons between diamond-bearing and barren bodies identify potentially useful exploration characteristics involving pipe and dyke geometry, olivine and phlogopite compositions, and the abundance and properties of pyrope and chromite. Diamond crystal forms, surface growth and dissolution features, and mineral inclusions are also reviewed. Basalts and their xenoliths provide sources of peridot, sapphire and zircon, with weathering producing secondary concentrations. Granitic pegmatites supply aquamarine, tourmaline, topaz, spodumene, quartz and other gem materials; the Altai pegmatites illustrate how internal mineral zoning controls the distribution of potential gemstones. A substantial discussion clarifies the mineralogical differences among materials sold or described as Chinese jade, distinguishing fei cui, nephrite, serpentine-rich rocks, altered gabbro, quartzite and compact chlorite. Hetian nephrite is characterized as predominantly tremolitic material associated with contacts between intrusive rocks and magnesium-rich carbonates, whereas Manas nephrite is related to alteration of ultrabasic rocks and is comparatively richer in iron. Descriptions of colour varieties, microscopic textures, associated minerals and comparative chemical analyses support these distinctions. Other resources include metamorphic kyanite, garnet and andalusite; hydrothermal agate, chalcedony, tiger’s-eye and carving stones; supergene turquoise; and placer deposits containing diamond, nephrite, sapphire, quartz and zircon. Chrysanthemum stone illustrates how similar decorative forms may comprise different minerals. Jet and amber are noted as organic ornamental materials. The final section briefly outlines Chinese production of synthetic ruby, sapphire, quartz and diamond, followed by other crystals used as gem materials. The survey emphasizes the breadth of China’s resources while acknowledging uneven knowledge of individual deposits and the variable gem quality of reported occurrences.

taaffeite, Sri Lanka, gems

Gübelin describes “taprobanite,” a rare red gemstone from Sri Lanka initially thought to be taaffeite because of its similar appearance and gemological properties. Detailed examination showed it to represent a distinct member of the taaffeite mineral group, characterized by differences in chemical composition, crystallographic properties, and optical behavior. The study discusses its identification, physical and optical constants, absorption characteristics, inclusions, and relationship to taaffeite, emphasizing the difficulty of recognizing such rare stones by conventional gemological testing alone. The name derives from Taprobane, the ancient name for Sri Lanka.

corundum, ruby, Pakistan.12, Hunza, gems

Discusses the gem resources of Pakistan, including Swat emerald and ruby in Hunza.

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

Sri Lanka is famous for having one of the greatest varieties of gemstones, all of which occur in placer deposits. Interestingly, the original host rocks have not yet been discovered. The geology consists largely of Precambrian formations, which can be divided into three major groups: the Highland Group, Southwest Group, and Vijayan Group. The principal gemstone-producing areas are the Ratnapura region in Sabaragamuwa Province, the vicinity of Elahera in Central Province, and the Tissamaharama region in Southern Province. This article describes the mining methods used in these major localities, the types of gemstone minerals found, and the inclusions observed within them.

corundum, treatments.6, gems

corundum, treatments.6, gems