corundum, beryl, emerald, inclusions, synthetic beryl, emerald, gems

This illustrated series presents gemstone inclusions as practical evidence for identification, distinguishing natural from synthetic stones, and interpreting the conditions under which gems formed. Drawn from Gübelin’s photomicrographic studies and a collection of Kodachrome transparencies supplied to the Gemological Institute of America, the installments combine explanatory text with photographs and descriptive captions. Microscopic examination, particularly with dark-field illumination, reveals structures that may be overlooked or misinterpreted with a loupe. The sapphire section illustrates oriented needles and silk, angular growth zoning, mineral crystals, fluid cavities, and featherlike networks. Examples include hematite plates, enclosed corundum crystals, and cavities containing liquid and gas. These features are compared with curved growth striae and gas bubbles in synthetic sapphire. Gübelin cautions that appearances can be deceptive: natural cavities may resemble bubbles, while the curvature of synthetic growth lines may be difficult to recognize within a small field of view. The ruby installment similarly contrasts natural rutile arrangements, straight structural features, mineral inclusions, and fluid-related formations with curved striae and concentrations of gas bubbles in synthetic material. Zircon inclusions surrounded by halos and intersecting rutile needles illustrate characteristic internal features of individual specimens from Sri Lanka and Myanmar. The emerald section describes enclosed crystals, irregular cavities, and inclusions containing liquid, gas, and a solid phase, while comparing these with wispy formations and other internal features observed in synthetic emeralds. The diamond installment demonstrates the importance of illumination when interpreting dark inclusions: objects commonly regarded as black or carbonaceous may prove to be transparent crystals when examined appropriately. Photographs show enclosed crystals, including diamond, together with cleavage features and fractures associated with inclusions or extending inward from the surface. Subsequent installments broaden the survey to additional sapphires and other gem materials. Illustrated examples include fine networks of channels, negative crystals, mineral plates, zircon-associated halos, liquid inclusions with mobile bubbles, and cavities containing separate liquids. Topaz and tourmaline provide further examples of fluid-bearing inclusions, while the concluding selection extends the illustrated material to emerald, peridot, quartz, garnet, and moldavite. Biotite flakes in peridot and fibrous actinolite in quartz demonstrate the variety of solid inclusions; a fluid-bearing negative crystal in citrine reproduces the host’s prismatic form. Throughout the series, the diagnostic value lies in the combined character, arrangement, and appearance of internal features rather than in an isolated resemblance. Gübelin advocates making inclusion study an early part of gem examination, potentially preceding routine measurements of physical and optical properties. The series also emphasizes the scientific and aesthetic interest of microscopic structures, presenting gemstone interiors as records of mineral growth and subsequent events as well as aids to identification.

geology, gems

Gübelin presents a schematic introduction to gemstone formation and deposits, using a circular diagram and an element-based table to make geological relationships more accessible to students of gemology. He emphasizes that such summaries necessarily simplify a complex subject but can clarify the individuality of gemstones, guide the practical study of deposits, and provide a foundation for further investigation. The classification distinguishes primary mineral formation from ascending solutions, termed magmatic in a broad sense, from secondary growth and concentration associated with decomposition, sedimentation, and metamorphism. Primary processes are subdivided into liquid-magmatic, pegmatitic and pneumatolytic, and hydrothermal and volcanic-exhalative categories. Secondary categories comprise chemical sediments derived from the atmosphere or hydrosphere, residual deposits produced through decomposition and metamorphism, and mechanically concentrated sediments, particularly alluvial deposits. The circular diagram places deposit types outside the circumference and representative gem materials within the corresponding sectors. Minerals occurring in more than one geological setting cross sector boundaries; corundum, spinel, and garnet are specifically identified as examples with multiple modes of occurrence. Related minerals are grouped according to chemical composition or paragenesis, while the more important gem materials receive typographical emphasis. Gübelin explains that the diagram favors practical usefulness over strict genetic classification. Thus, amber and jet are placed among metamorphic formations, while pearls and corals appear among chemical sediments, although he explicitly recognizes their organic origin. The accompanying table develops the survey through chemical elements, linking important minerals with magmatic, sedimentary, residual, and metamorphic settings. It includes familiar gems such as spodumene, tourmaline, beryl, chrysoberyl, corundum, diamond, quartz, opal, zircon, turquoise, and garnet, together with less common ornamental minerals and several metallic minerals. Separate columns indicate the different processes through which these materials may form or become concentrated. Notes draw attention to the production of aluminum-rich residues by weathering and their subsequent metamorphic transformation, the role of atmospheric carbon in carbonates and organic materials, and the redistribution of certain minerals into alluvial deposits. The inclusion of rare elements requires reference to some uncommon gem materials, but the author stresses that neither the mineral list nor the deposit classification is exhaustive. Together, the diagram and table offer a condensed teaching aid connecting gemstone chemistry, mineral associations, formation processes, and economically relevant occurrences, intended as a starting point for more detailed geological study.

jade, jadeite, fei cui, nephrite, Burma, China, jade carving, Chinese jade, gems

W.L. Hildburgh examines Chinese snuff-bottles carved from parti-coloured hardstones, emphasizing the lapidary’s ability to transform natural layers, stains, inclusions, and irregularities into coherent decorative designs. Extending an earlier discussion of Chinese hardstone carving, he argues that these small utilitarian objects often display exceptional artistic invention alongside technical mastery. He explains that the exterior is completed before hollowing begins, allowing the craftsman to investigate colour distribution, exploit useful features, and remove defects before undertaking the lengthy excavation of the interior. Reports from carvers using treadle-driven tools suggest that shaping and ornamenting a fine bottle could require ten to fifteen days, with another ten to thirty days devoted to hollowing and internal polishing. Thin walls enhance translucency, reduce weight, and demonstrate skill, while the precision achieved inside opaque or awkwardly shaped vessels reflects sophisticated control of tools and material. Hildburgh distinguishes several approaches to coloured decoration. Contrasting layers may be carved in rounded cameo relief against a relatively uniform body, as in agate bottles bearing horses, birds, bamboo, or a cricket among vegetables. Rock crystal with adhering white quartz matrix provides another combination, with the matrix shaped into trees, animals, and figures; one smoky-quartz example retains the crystal’s natural hexagonal form beneath carved decoration on all six faces. More complex stones permit the coordination of several coloured strata, variations in translucency, and differentiated polish within a single composition. Hildburgh also notes that separately carved reliefs may be cemented over flaws so skilfully that the repair is difficult to detect. Where colour occurs only in a thin surface concentration, the carver must preserve its irregular level and avoid rounding edges that would expose the underlying body colour. The article’s most sustained analysis concerns agates containing dispersed dark markings. Here the craftsman selectively lowers and shapes the surface to reveal coloured areas at different depths, adjusting their contours and opacity to create silhouettes, figures, foliage, birds, and landscape effects. Some natural formations remain untouched, while others are integrated with carefully worked details. Hildburgh contrasts this responsive manipulation with European uses of patterned stones, crediting Chinese carvers with an unusually sensitive appreciation of each specimen’s individual possibilities. Throughout, he stresses that photographs inadequately convey many effects dependent on subtle colour, translucency, depth, or decoration extending around the vessel. The study presents successful snuff-bottle carving as an accommodation between the demands of handling, the geological character of the stone, and the craftsman’s imaginative interpretation.

corundum, synthetic corundum.7, synthetic spinel, inclusions.5, gems

Gübelin describes unusual gas inclusions in synthetic corundum and spinel that closely resemble fluid inclusions in natural gems, emphasizing the need to examine their contents and optical behavior rather than identify origin from shape alone. Natural and synthetic corundum have closely similar chemical and physical properties, while differences in refractive index and luminescence may be too small or overlapping to provide decisive evidence. Microscopic characteristics therefore assume particular importance. The author reviews natural corundum’s oriented rutile needles, other mineral inclusions, fluid cavities, and growth structures, contrasting these with the curved striae and rounded gas bubbles commonly associated with synthetic material. He cautions that twinning occasionally occurs in synthetics and that internal cracks near facet junctions can result from strain in either natural or synthetic stones. Recent examinations revealed rare, irregular gas cavities, particularly in blue synthetic sapphires, with elongated, tubular, wormlike, dendritic, and mesh-like forms. Some resemble coarse liquid feathers in natural corundum so closely that they could lead to misidentification. Small accompanying spherical bubbles and, in one illustrated specimen, curved striae exposed by closing the microscope’s iris diaphragm provide additional evidence of synthetic origin. Dark, hazy areas in another sapphire are attributed to localized concentrations of coloring material. Gübelin distinguishes the illustrated gas-filled cavities from natural liquid inclusions by rotating the stone in an immersion cell: the gas inclusions remain black, whereas liquid-filled cavities appear transparent when viewed through their flat sides and may contain a separate gas bubble. He notes that such deceptive forms were uncommon at the time but might become more frequent as manufacturing improved. The discussion then turns to synthetic spinel, whose variable excess of aluminum oxide affects refractive index and specific gravity, limiting reliance on these properties alone. Although curved striae are absent, occasional gas inclusions may likewise be elongated, wormlike, sharply outlined, or apparently oriented. Anomalous double refraction caused by internal strain offers a further means of recognition. Under polarized examination, synthetic spinel displays incomplete extinction and irregular bright and dark patterns, including cloudy, fibrous, feathery, and crosshatched appearances. The author contrasts these with the weaker, indistinct, blotchy anomalous double refraction sometimes observed in natural spinel, commonly associated with solid or fluid inclusions. He also distinguishes the latter from the more checkered patterns seen in garnet. The article concludes that characteristic strain patterns, considered together with inclusion morphology, cavity contents, and other microscopic evidence, permit recognition of synthetic material despite its potentially deceptive resemblance to natural gems.

beryl, emerald, Russia, Colombia, inclusions, gems

Gübelin investigates microscopic criteria for distinguishing emeralds from Colombia and Russia’s Ural Mountains, arguing that color alone provides an unreliable indication of origin. Although Colombian emeralds are associated with a velvety green and Russian stones with more yellowish hues, examples from either source may resemble those from the other, particularly in small sizes. A comparative table records their appearances through several colored filters, but the author emphasizes that interpreting these subtle differences requires considerable experience, a sensitive eye, and suitable comparison material. Seeking more objective evidence, he examined numerous emeralds of known provenance, including specimens supplied by the Colombian Consulate in Paris. He identifies minute fluid inclusions, rather than conspicuous fractures or cloudy areas, as the most useful distinguishing features. Colombian emeralds are described as containing scattered, irregular groups of delicate, frequently tail-like cavities. Their boundaries are faint, suggesting that the enclosed liquid has a refractive index relatively close to that of the host. The liquid’s composition was not established, although behavior during heating and considerations of formation led the author to suggest water. The cavities show no consistent crystallographic orientation and remain separate even when grouped. Almost every cavity is reported to contain a tiny cubic crystal, commonly adjoining a rounded gas bubble with a dark outline, so that solid, liquid, and gaseous phases coexist within one inclusion. Carbon dioxide is proposed as the gas, while the solid’s chemical identity remains unresolved. Gübelin regards the cubic form of this solid inclusion as the principal diagnostic feature of Colombian material. Russian emeralds likewise contain multiphase inclusions, but their distribution, cavity shapes, and enclosed crystals differ. Their cavities are more closely associated with fractures and moss-like internal features, lack the characteristic Colombian tails, and contain solid crystals displaying lozenge-shaped or rhombic outlines rather than clearly rectangular cubic forms. The author presents this contrast as a dependable means of separating the two sources and supplies a mnemonic linking Colombian origin with cubic crystals and Russian origin with rhombic crystals. He recommends photomicrography to document the observations and notes that the features can also be examined with a diamondscope. The concluding discussion separates geographical interest from intrinsic quality: identifying a fine emerald as Russian need not diminish its value, while knowledge of provenance may increase an owner’s appreciation of either a Colombian stone or an unusually fine-colored Ural specimen.

corundum, properties.3, gems

Walcott investigates asterism in garnet, spinel, quartz and sapphire through microscopic observations, measurements of angular relationships, and geometrical reconstructions of luminous bands on spheres and crystal models. His principal aim is to relate star patterns to crystallographic symmetry and to identify the internal structures responsible for their formation. Two almandine garnet spheres in the Field Museum display four great-circle chatoyant bands intersecting to produce twelve four-rayed stars, each with alternating angles of 70°32′ and 109°28′. These bands are associated with fine elongated inclusions oriented parallel to the crystal’s threefold symmetry axes. A garnet cabochon possesses an additional inclusion system parallel to the fourfold axes, producing a combination of four- and six-rayed stars. A dark-red spinel cabochon contains inclusions aligned with the twofold symmetry axes; projected onto a complete sphere, its six bands would generate eight six-rayed stars with 60° angles and six four-rayed stars with 90° angles. These observations directly challenge the assumption that cubic minerals can exhibit only four-rayed stars with right angles. Walcott develops a classification of possible inclusion arrangements parallel to the three classes of symmetry axes in the hexoctahedral crystal class, considering both complete and incomplete sets and their combinations. He calculates a minimum of 179 possible arrangements, while distinguishing the few represented by available specimens from hypothetical configurations. The most elaborate configuration considered would produce thirteen great-circle bands and combinations of six- and eight-rayed stars. Turning to colourless quartz, rose quartz and sapphire, he describes three intersecting bands forming six-rayed stars at the poles of the crystallographic c-axis. Restricted illumination reveals fine internal striae that he interprets as surface growth striations incorporated into the crystal during oscillatory development of different crystal forms. In sapphire, he further suggests that some striae lengthened through minute cracks associated with metamorphism. He attributes the greater abundance of star sapphires than star rubies to differences in prevailing crystal habits and their propensity to develop striations. Variations in the fineness, continuity and arrangement of these structures are used to explain sharply defined, broad or feathery star bands, while zoning, twinning and other inclusions may diminish their brightness. A predominantly single directional system can produce a sapphire cat’s-eye when appropriately cut. Throughout the study, Walcott interprets asterism chiefly as a diffraction phenomenon, supported by transmitted-light stars in quartz and spectral colours observed in sapphire bands. The paper combines documented observations with geometrical predictions and proposed explanations for the origin of the structures producing the optical effects.

gems, Arabic mineralogy, al-Biruni, rock crystal, glass

Kahle presents and translates sections of al-Bīrūnī’s eleventh-century Kitāb al-jamāhir fī maʿrifat al-jawāhir dealing with rock crystal, glass, enamel/glass fluxes (mīnā), and ruby glass (adrak), using two manuscripts and emphasizing the value of al-Bīrūnī’s account for understanding the materials and techniques represented among the Fatimid treasures. Rock crystal is described as a transparent, colorless stone prized for vessels, hardness, clarity, and resemblance to water and air; al-Bīrūnī discusses its sources, working, value, inclusions, and supposed formation, including contemporary observations and historical anecdotes concerning valuable crystal vessels. Glass is described as produced by melting quartz or sand with alkali, prolonged firing increasing its clarity and hardness; properly made colorless glass could approach rock crystal in transparency, though its greater abundance and softness reduced its value. Particularly important is al-Bīrūnī’s treatment of mīnā, explicitly described as a type of glass, softer and heavier according to its lead content. He records recipes employing finely powdered quartz or rock crystal with red lead or tin oxide, together with natron or borax-type fluxes, and gives coloring materials: lead compounds for yellow, copper compounds for green, burned brass for red, iron residues for black, manganese for wine-purple, lead white for white, burned gold for ruby color, and lapis lazuli and carnelian for violet. Kahle notes that these descriptions strongly support the interpretation of mīnā in Fatimid inventories primarily as enamel or vitreous flux. The final section discusses adrak, an ancient Alexandrian red or garnet-colored glass reportedly comparable in appearance and value to ruby and whose manufacture was said already to have been lost by the ninth century; al-Bīrūnī preserves several recipes or traditions for attempting its production, along with observations on other artificial colored materials, mosaics, and objects recovered from ancient Egyptian and Yemeni burials.

corundum, ruby, Thailand.12, Cambodia.12, Siam, inclusions.5, gems

gems, ruby, synthetic ruby, treatments.6, chromium, corundum, sapphire, fluorescence, absorption spectrum, ultraviolet light, emerald, beryl

The ruby is a mineral composed of aluminum oxide with traces of chromium oxide which gives it its color. The pigment is very probably in molecular solution. As aluminum oxide has a strong crystalline urge, the ruby is quite easily obtained synthetically by just fusing its components in an oxygen-hydrogen flame. The product thus obtained differs but little from the natural ruby, as far as chemical and physical properties are concerned. Its color is produced in distinct zones which are curved instead of being straight as is the case with real rubies. While the real material contains inclusions which are peculiar to certain proveniences, the synthetic stone is rather clean except that it contains gas bubbles which render it at times unfit for technical uses as for jewels, etc. Both, the real and synthetic rubies, exhibit the same properties when heated to high temperatures. They turn a dull deep red and cool, via a greenish state (near 600 degrees C.). The color, after heating, is identical to the original color. The pigment is, therefore, very closely attached to the molecule and is probably isomorphously mixed. There exists only one analysis showing a trace of chromium but recent spectroscopic investigations have revealed that all pink corundums contain some chromium, i. e., the rose Montana sapphire, the pink Ceylon sapphire, and the blue Ceylon stone with a purple tinge (this variety loses its blue color when heated and the result is a rose sapphire the color of which is stable). Ruby fluoresces when exposed to ultra violet light of an iron arc or of a mercury vapor lamp. The color which it emits is of a deep red and this red light is excited by the invisible ultra violet rays as well as by green light. The same fluorescence can be observed with emeralds which also owe their green color to an addition of chromium, but here, to the silicate molecule. A plate of ruby placed between a source of white light and a spectroscope which allows the white light to be fanned into a band showing the spectrum colors, red, orange, yellow, green, blue and violet, shows that some of the light rays are absorbed by the ruby molecule. Thus all violet rays and part of the green rays are held back or filtered off. Besides, certain distinct wavelengths are absorbed and closer investigation shows that some red light waves are filtered off. There are two sharp absorption lines in the red part of the spectrum and these coincide with the red lines emitted under the influence of ultra violet light. The emission and absorption lines are identical. This is of high scientific importance. Emerald shows the same phenomenon. Besides visible light, the ruby also filters off some of the ultra violet invisible rays emitted by a carbon arc containing iron or nickel. Recent investigations along these lines have revealed that the transparency of the synthetic material is greater than that of the real stone. The higher absorption of the latter is probably due to a certain iron content which tends to absorb ultra violet light as is shown by glass which invariably contains iron and is more or less opaque for ultra violet light. Expressed in terms of spectrum measurement the absorption of the synthetic ruby begins at a region near 2700 Angstrom Units while that of the real ruby begins near 3200. A spectrum taken with a plate of ordinary glass would be still shorter than that of the real ruby; glass absorbs even more ultra violet rays. The spectrum would end somewhere near the heavy line bordering the absorption regions of the synthetic ruby spectrum. It would, however, let those violet rays pass which we find filtered off by the rubies so that we would find a continuous band from the red end down to the point indicated.

corundum, inclusions.5, Burma.12, Sri Lanka.12, Thailand.12, gems

Escard provides a concise survey of the ruby, describing its varieties, physical properties, geographical sources, mining, cutting, valuation, and methods of distinguishing natural stones from imitations and artificial products. [655] He identifies ruby as red corundum and discusses differences in color among rubies from Burma, Siam, and Ceylon, noting that terminology such as “Oriental ruby” and “Siam ruby” was often applied inconsistently in commerce. [656] Particular attention is given to microscopic examination: natural rubies may contain crystalline inclusions and other internal features, while differences in color and dichroism can help separate stones from different sources; illustrations show characteristic inclusions and a Ceylonese lapidary at work. [657] Escard discusses the distinctive internal structure of Burmese and Siamese rubies, differences observed with the dichroscope, and variations in specific gravity, accompanied by photomicrographs and a map of the ruby-bearing district of Burma. [658] Fluorescence and phosphorescence are described as useful diagnostic properties, Burmese rubies showing particularly strong fluorescence; the principal ruby deposits are said to occur in Burma and Ceylon, where ruby-bearing gravels are washed and sorted, with an account of mining and recovery methods in the Mogok district and illustrations of the Burmese mines. [659] The article gives production and value figures for Burmese ruby mining, mentions occurrences in Ceylon, Siam, Afghanistan, and elsewhere, discusses the considerable variation in value according to color, quality, and size, and briefly describes cutting practices, including the preference for the oval form. [660] Escard concludes with remarks on celebrated rubies, including stones associated with European collections, and emphasizes the commercial importance of distinguishing natural rubies from artificial stones, illustrating a certificate of authenticity for a natural Burmese ruby.