corundum, ruby, sapphire, synthetic corundum.7, synthetic ruby, synthetic sapphire, gems

Chudoba and Gübelin provide a practical guide to distinguishing natural gemstones from synthetic counterparts, combining a short history of artificial gem production with detailed discussion of the principal manufacturing methods and their diagnostic consequences. The Verneuil flame-fusion process, flux growth, and hydrothermal synthesis are described, together with the characteristic structures and inclusions they produce. Particular attention is given to synthetic ruby and sapphire, spinel, emerald, and other important gem materials, with comparisons between natural and laboratory-grown stones based on growth zoning, curved striae, gas bubbles, mineral inclusions, refractive properties, fluorescence, and other microscopic and physical features. The authors emphasize examination with the gemological microscope as one of the most powerful means of separation, supported by numerous photomicrographs illustrating inclusions and growth phenomena in both natural and synthetic gems. Conceived as a concise working manual for gemologists and jewelers, the book brought together the principal identification criteria then available at a time when synthetic gemstones were becoming increasingly sophisticated and commercially important.

jade, jadeite, fei cui, California, gems

R.G. Coleman describes the geological occurrence, mineralogical properties, and ornamental potential of jadeite from the Clear Creek region of San Benito County, California. After distinguishing jadeite from nephrite and other green minerals marketed as jade, he reviews discoveries of jadeite-bearing boulders and bedrock exposures and reports additional occurrences, including a large isolated mass near Santa Rita Peak. The deposits lie within an elongated serpentine body forming a dome bordered by sedimentary rocks. Jadeite occurs principally in two settings: zoned, lenslike bodies enclosed by serpentine, and veins cutting schist masses within it. The lenses contain outer zones rich in prehnite, hydrogarnet, and sphene, an intermediate zone dominated by thomsonite, and a central mass of fractured green jadeite subsequently healed by white jadeite. Veins occur mainly near the margins of albite-acmite schist bodies, generally measure less than an inch across, and locally widen to eight inches. Larger veins likewise preserve an older green generation cut by younger white jadeite, whereas smaller white veins show relatively little subsequent deformation. Chemical analysis, optical measurements, density determination, and X-ray powder diffraction establish that the white material closely approaches pure jadeite. Its density is approximately 3.43, and its principal refractive indices are about 1.654, 1.657, and 1.666. The associated green jadeite contains appreciable diopside and acmite components; Coleman attributes its colour principally to iron incorporated through the acmite component. Despite the mineralogical purity of some material, the deposits had not yielded the emerald-green colour characteristic of imperial jade or abundant large masses of uniform appearance. Two-stage crystallization commonly produces contrasting colours and textures, with fine-grained green jadeite interrupted by coarser white material. Nevertheless, selected small pieces can produce attractive cabochons, and the green variety polishes more readily than the white. Variegated and brecciated boulders reaching three feet across offer possibilities for polished slabs. Coleman concludes that the locality has value as a source of lapidary material and potentially small ornamental pieces, while emphasizing the scarcity of uniformly high-quality masses, the difficulty of quarrying exceptionally tough rock, and the untested possibility that further exploration at depth might reveal better material.

ruby, sapphire, corundum, Burma.12, gems

Reports on a visit to Mogok and its surrounding gem fields in autumn 1955, describing travel conditions, mining and the local gemstone industry. Lists the gem minerals recovered and explains traditional cutting practices and bargaining by concealed hand signals beneath a cloth. Also warns of synthetic corundum tumbled to resemble natural ruby rough.

corundum, Australia.12, gems

Chalmers surveys the occurrence, mining history, geological setting, and gem quality of diamonds, opals, sapphires, rubies, spinels, and beryls in New South Wales, drawing on published accounts, museum specimens, and personal observations. The principal historical diamond fields are Cudgegong, Bingara, and Copeton, where diamonds occur in ancient river gravels, commonly beneath basalt, and in younger deposits derived from their erosion. Recovery from gold-dredging operations near Wellington represents a more recent development, although the material is predominantly industrial quality. The author reviews competing explanations for the diamonds’ primary origin, including early suggestions of formation within the gravels, derivation from metamorphosed sediments, and association with basic igneous rocks. Reports of diamonds in volcanic breccia and dolerite are discussed cautiously because subsequent discoveries have not supplied adequate confirmation. New South Wales diamonds are generally small but commonly of good quality, with yellow and other colors recorded; claims of exceptional hardness are qualified by the directional nature of diamond hardness and conflicting experimental observations. Opal occurrences are divided between relatively restricted deposits in igneous rocks and the economically important sedimentary fields. At Tintenbar, precious opal occupies cavities in decomposed basalt, but its tendency to crack curtailed mining. White Cliffs and Lightning Ridge occur in Lower Cretaceous sedimentary rocks, principally clayey sandstones associated with silicified marker beds known as bandstone. At White Cliffs, precious opal occurs within common opal along bedding planes and joints and replaces fossils, wood, and minerals, including the distinctive pseudomorphs called opal pineapples. Lightning Ridge, especially noted for black opal, produces isolated nodules known as nobbies. The widespread distribution of suitable sediments suggests possibilities for further discoveries. Sapphire is chiefly recovered from ancient or reworked gravels, particularly in the New England district. Stones include very dark blue, green, yellow, and parti-colored material; microscopic observations reveal minute vesicular inclusions, rutile, and color banding, although their diagnostic significance remains unproven. Opaque bronze-colored chatoyant corundum also offers possibilities for cutting black star sapphires. Chalmers questions many older ruby and spinel identifications, noting that pale-pink corundum is not true ruby and that some reported material was probably garnet or zircon, while small red spinel crystals have been confirmed by testing. Beryl occurs in pegmatites around Emmaville and Torrington, with transparent pale yellowish-green, deep-green, and golden material represented in museum collections. A small emerald industry near Emmaville operated intermittently between 1890 and 1909. These emeralds are comparatively pale, and the article records their filter reaction, relatively low specific gravity, and refractive index, placing the deposits’ commercial history alongside their mineralogical characteristics.

gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology

Costa Rican jade ornaments have been known chiefly through collections made by Padre José Maria Valasco in the Nicoya peninsula, which forms the northwestern corner of the country, and through the subsequent publication of these specimens by C. V. Hartman (1907). The Velasco jade is now in the Museo Nacional at San José and the Carnegie Museum of Pittsburgh.The term jade is loosely used by archaeologists. Hartman employed it to describe 3 minerals: a blue-green jadeite, saussurite, which in Costa Rica usually is blue-green with white spots, and a dark green bowenite. These shades are characteristic of Nicoya specimens but not of the jades of northern Central America and Mexico. More recently, W. F. Foshag has identified the principal minerals used for ornaments in Costa Rica as diopside-jadeite and chalcedony (Anonymous 1947, Specimens 1-7, 15-18).

gems, amblygonite

Gübelin describes transparent amblygonite as a potential gemstone, drawing attention to gem-quality material recognized during mineralogical research rather than through the discovery of a new deposit. In early 1953, G. Bottcher, a mineralogy student in Hamburg investigating the optical properties and orientation of spodumene, encountered pale-yellow crystals that A. Schroder identified as amblygonite. Although already well known as an economically important lithium mineral, amblygonite had received little attention as a faceted gem. Its composition, LiAl(OH,F)PO₄, permits variation through substitution between hydroxyl and fluorine, accompanied by changes in optical properties and specific gravity. The transparent material ranges from colorless to golden yellow, with pale yellow predominating, and resembles similarly colored spodumene. The crystals are triclinic and commonly have a slab-like habit. Gübelin distinguishes amblygonite’s single basal cleavage from the two cleavage directions of spodumene and reports that attractive stones have nevertheless been successfully faceted. With a Mohs hardness of 6, he considers the material suitable for wear. Measurements of the cut specimens are comparatively consistent, with average principal refractive indices of approximately 1.612, 1.621, and 1.636, birefringence near 0.026, and specific gravity between 3.01 and 3.03. The mineral is optically positive, with an optic axial angle of approximately 79°44′, compared with about 58° for spodumene. Microscopic examination reveals characteristic cloudy arrangements that may occupy most of a stone or form parallel and intersecting bands. At greater magnification, these clouds resolve into numerous minute cracks accompanied by particulate impurities resembling brown or black grains of sand; the particles are not mineralogically identified. Under long-wave ultraviolet radiation, the specimens exhibit faint, dirty greenish-yellow fluorescence. To verify the identification, Gübelin compares an X-ray powder diffraction pattern of the gem material with that of established amblygonite from Trujillo, Spain, recorded under identical conditions. Their agreement confirms that the transparent material is amblygonite. The article provides comparative physical measurements, photomicrographs of the inclusions, diffraction photographs, and a table of measured lattice spacings and relative line intensities. Determination of the lattice constants is deferred because of the triclinic structure and the difficulty of orienting an irregular fragment for rotation photography without a suitably developed crystal. Gübelin concludes that transparent amblygonite adds an interesting species to the range of gemstones, while judging that its probable scarcity will restrict its importance chiefly to collectors and gemologists rather than support a substantial public market.

corundum, ruby, sapphire, inclusions.5, phenomena, star, gems

A.S. Tait investigates the cause of asterism in corundum, testing competing explanations involving twinning lamellae, microscopic cavities, and regularly arranged solid inclusions. The study draws on extensive rough and cut material from Montana, North Carolina, Ceylon, Siam, Burma, and Queensland, with basal thin sections permitting examination of inclusion arrangements in transmitted and reflected light without the distortion introduced by curved gemstone surfaces. Microscopic observations show that star-producing material contains rodlike or needlelike inclusions arranged in the basal plane, parallel to the hexagonal prism faces and intersecting in three directions at 60°. When these inclusions are sufficiently abundant and evenly distributed, a cabochon cut with its axis parallel to the crystal’s optic axis displays a six-rayed star. Stars formed in water droplets placed on thin sections provide a direct demonstration linking the optical effect to the included material. Tait also identifies a second set of basal inclusions oriented perpendicular to the first-order prism faces. Although generally too sparse to produce visible rays, these offer an explanation for twelve-rayed stars when sufficiently concentrated alongside the principal set. Determining the inclusions’ mineral identity proves more difficult. At magnifications up to 900×, they appear reddish brown in transmitted light and show apparently square cross-sections, suggesting rutile, but their fineness prevents reliable refractive-index measurement. Microchemical analysis and X-ray powder examination fail because the quantity of included material is too small. Spectrographic analysis therefore compares carefully prepared samples ranging from apparently inclusion-free corundum to heavily included star-producing material. The latter contains titanium at approximately 0.001% and iron at approximately 0.009%, with traces of chromium; the apparently inclusion-free material shows aluminium with traces of chromium and iron. Combining the titanium detection with the observed colour and crystal habit, Tait identifies the needles as rutile, excluding other titanium dioxide minerals on morphological grounds. The article concludes that symmetrically oriented rutile needles account for the asterism of the material examined. Photomicrographs further relate optical appearance to inclusion distribution: predominantly one-directional concentrations produce a cat’s-eye effect, localized arrangements restrict where a star can be obtained, and uniformly distributed needles permit star formation across suitably oriented portions of the crystal.

China, central Asia, Marco Polo, gems

Shor recounts her travels with her husband, Franc, in an attempt to retrace Marco Polo’s route from Venice to China, combining personal adventure, historical comparison, and observations of societies undergoing rapid political change. Opening with a dangerous episode in the Pamirs, where Franc lies seriously ill, she returns to her childhood fascination with exploration, wartime Red Cross service in Italy, and postwar relief work in China. Experiences in Shanghai and Peiping, detention by Communist forces, and a journey across the Gobi establish the background to the couple’s more ambitious expedition. Their subsequent route leads through Turkey, Iran, and Afghanistan toward the Wakhan and Hunza, using whatever transport circumstances permit, from motor vehicles to horses and yaks. Marco Polo’s narrative supplies a continuing point of reference for landscapes, trading centres, local products, and customs, although modern borders, military restrictions, and diplomatic requirements repeatedly complicate attempts to follow his itinerary. Encounters range from conversations with villagers, merchants, guides, and pastoralists to audiences and social occasions with the Shah of Iran, the King of Afghanistan, and the Mir of Hunza. Of particular gemological interest is the account of privileged access to Iran’s crown jewels at Bank Melli in Tehran. Shor describes the elaborate security arrangements, masses of loose gemstones and pearl strands, royal crowns, an emerald-topped snuffbox, a turquoise-decorated gold bowl, and the Daria-i-noor diamond. She records explanations and legends supplied during the visit concerning the treasures’ origins, acquisition, value, and role as backing for the national currency; these passages are eyewitness travel impressions and reported accounts rather than a systematic gemological catalogue. In Afghanistan, the purchase of an inexpensive piece of lapis lazuli and an unsuccessful search for a balas ruby prompt comparisons with Marco Polo’s descriptions of mineral wealth and royal restrictions on gemstone extraction and export. The expedition’s most sustained ordeal unfolds in the Wakhan, where difficult terrain, uncertain supplies, negotiations over transport, severe weather, and illness expose the travellers’ dependence on local assistance. Their intended continuation into China is ultimately prevented by political upheaval and the closure of the frontier, although they reach the crest of the Mintaka Pass before turning back. A concluding stay in Hunza provides observations of agriculture, hospitality, domestic life, government, and polo, contrasting the valley’s relative isolation with the pressures of the surrounding world. Written in an energetic, humorous, and strongly personal voice, the book presents travel as a pursuit sustained by curiosity and human generosity, while its depictions of Asian peoples and political events reflect the author’s American perspective during the early Cold War.

gems, gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology, Pre-Columbian jade; Costa Rica; Maya; exchange; iconography, lapidary

Studied numerous smaller jade carvings in order to establish lapidary methods, as illustrated by the pen-and-ink drawings. Discusses the jades of the Maya culture and those of the Valley of Mexico and Oaxaca, together with excellent Olmec objects from the La Venta culture. Features excellent drawings; photographic plates consist mainly of jade carvings.

corundum, inclusions.5, gems

F.G. Smith’s Historical Development of Inclusion Thermometry is a comprehensive historical and critical review of the use of inclusions in minerals to determine the temperatures and pressures prevailing during crystallization. Drawing upon more than a century of mineralogical, petrographic, and physicochemical research, the book traces the development of inclusion studies from the early nineteenth century through 1953, emphasizing their importance in understanding mineral genesis, hydrothermal processes, pegmatite formation, and ore deposition. Smith reviews the pioneering investigations of Humphry Davy, David Brewster, Henry Clifton Sorby, Ferdinand Zirkel, William Noel Hartley, and numerous later researchers, showing how microscopic observations of trapped fluids, gases, and solids gradually developed into quantitative methods of geological thermometry. Particular attention is given to Sorby’s groundbreaking work of 1858, which established the relationship between the expansion of fluids in sealed mineral cavities, the disappearance of vapor bubbles during heating, and the temperature and pressure of mineral formation. The book examines the classification of primary and secondary inclusions, the mechanisms by which foreign substances become enclosed during crystal growth, and the effects of subsequent recrystallization, deformation, and fluid leakage. Extensive discussion is devoted to aqueous inclusions containing dissolved salts, inclusions containing liquid carbon dioxide, multiphase inclusions with daughter crystals, and glassy inclusions representing trapped silicate melts. Smith evaluates the physical chemistry of water–carbon dioxide systems, the influence of pressure on homogenization temperatures, and the limitations of using such temperatures directly as measures of crystallization conditions. He also reviews decrepitation techniques, in which minerals are heated until internal pressure causes inclusions to rupture, providing another means of investigating their thermal histories. Of particular gemological interest are the numerous historical observations of inclusions in ruby, sapphire, spinel, emerald, aquamarine, topaz, quartz, diamond, garnet, and tourmaline. Smith recounts Brewster’s early experiments with fluid inclusions in topaz and sapphire, including observations of highly expansible liquids subsequently identified as carbon dioxide. The investigations of Sorby and Butler in 1869 receive special attention, particularly their descriptions of two- and three-phase inclusions in ruby and sapphire, complex inclusions in spinel, and fluid and crystalline inclusions in emerald and aquamarine. Studies of oriented mineral inclusions, internal strain, radial fractures, and their relationships to asterism and chatoyancy are also reviewed. Smith discusses the contributions of Eduard Gübelin to the identification and interpretation of inclusions in gemstones, recognizing their significance in distinguishing natural materials from synthetic counterparts and understanding the geological environments in which gems crystallize. The concluding critical synthesis examines the classification and formation of inclusions, the nature of mineral-forming solutions, and the principles and limitations of inclusion geothermometry. Extensive bibliographies arranged by author and subject make the volume an important reference to the early scientific literature. The work provides a valuable historical foundation for modern fluid-inclusion studies and gemological microscopy, documenting the development of techniques that permit microscopic features within crystals to reveal information about their origins and conditions of formation.