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.