gems, corundum, chemistry.2, history of gemology, history of crystallography

This book is designed for the first part of a modern course on the physics of solids. It has been written from the author’s lecture notes for the first semester of a three-semester sequence on solids offered by the Physics Department at the University of Illinois. This first course is taken mainly by graduate students who have had an introductory course in quantum mechanics and the standard background of undergraduate physics courses including thermodynamics and elementary statistical mechanics.

gems, ancient gemology, ancient jewelry, Greece, Greek, Egyptian, gold jewelry, Alexander the Great

Until recently, our understanding of early Hellenistic jewelry relied almost entirely on the spectacular Greek gold finds made in South Russia during the nineteenth century, now housed in the Hermitage Museum. Between the two world wars, similar discoveries emerged in northern Greece—particularly in Thessaly and Macedonia—thanks to finds by local peasants. The most notable hoards, reportedly from Carpenisi and Demetrias, were divided between the Benaki and Stathatos collections in Athens, the latter now part of the National Museum. While the Hermitage’s holdings are primarily known through nineteenth-century publications and travel to Leningrad, the Benaki and Stathatos gold has been well documented in two exemplary catalogues. Nonetheless, knowledge of Greek jewelry from the Age of Alexander remained fragmented. In the past decade, however, this picture has changed dramatically. A wave of important discoveries—largely from clandestine excavations in northern Greece, Asia Minor, and other regions—has entered both private and institutional collections in Europe and America, while official excavations have also yielded substantial new material, much of which remains unpublished or entirely unknown. The exhibition Greek Gold from the Age of Alexander was conceived to bring together, for the first time, many of these remarkable works. Of the 148 groups of objects selected, 83 come from private collections, 68 are illustrated here for the first time, and three-quarters have never before been publicly exhibited. Dr. Herbert Hoffmann, drawing on his deep expertise and familiarity with European collections, assembled one of the most impressive displays of Greek jewelry ever seen. During a year at the University of Heidelberg’s Institute of Classical Archaeology, he traveled extensively across Europe to secure loans for the exhibition. Patricia F. Davidson, Research Associate at The Brooklyn Museum and a trained goldsmith, contributed her specialized knowledge of ancient techniques, reproducing methods based on her microscopic analyses using tools and materials believed to be historically accurate. She was assisted by William J. Young, Head of the Research Laboratory at the Museum of Fine Arts, Boston, who used X-ray fluorescence and other non-destructive tests to analyze alloy and inlay compositions. The catalogue addresses not only the stylistic, historical, and iconographic aspects of Hellenistic gold but also its technology, with schematic drawings by Suzanne E. Chapman of the MFA, Boston, some based on sketches by Helmut Prüickner of Heidelberg University.

synthetic corundum.7, synthetic ruby, hydrothermal, gems

A hydrothermal ruby acquired by the Gemmological Association is described, with emphasis on the microscopic features distinguishing its natural seed from the synthetic ruby grown around it. The specimen had a relatively thick hydrothermal overgrowth deposited on a natural ruby core. Examination by E. Gübelin confirmed observations he had published in 1961 on hydrothermal ruby produced in the United States. Under dark-field illumination, the seed was readily visible and clearly distinguishable from the surrounding synthetic material. Its natural inclusions consisted of microlites surrounded by liquid films, whose appearance led Gübelin to suggest that the seed was probably a ruby from Siam, now Thailand. The geographical attribution was tentative and based on the appearance of the natural inclusions. The hydrothermal overgrowth contained characteristic gaseous markings, illustrated as irregular tubes and hose-like forms. Photomicrographs taken in transmitted light showed these inclusions and their relationship to the natural core. Dark, paired growth lines meeting at angles characterised the natural seed, while numerous gaseous inclusions occurred along the boundary between the seed and its synthetic overgrowth. A further illustration showed the overall distinction between the two components and the natural inclusions retained within the core. The specimen’s physical properties corresponded to those reported by Gübelin in 1961, although numerical measurements were not supplied in this account. Its colour was dark red, an appearance the report considered sufficient to arouse suspicion. Nevertheless, a gemmologist who examined it briefly under a microscope incorrectly concluded that it was natural. This incident demonstrates the identification problem presented by a synthetic overgrowth surrounding a naturally included seed: observing natural inclusions in one part of a stone does not establish that the entire specimen is natural. The report therefore stresses careful microscopic examination before determining a ruby’s nature, particularly recognition of the boundary between the core and overgrowth and the contrasting inclusion populations on either side. Dark-field illumination was especially effective in revealing this distinction.

jade, nephrite, USA, California, gems

Diamonds are said to be forever, but there are very few gemstone materials about which there has developed throughout the ages such a curious lore as there has about jade. In California, this lore has attracted statewide attention, principally because deposits containing the jade minerals, jadeite and nephrite, occur at several places throughout the state and because gem or lapidary quality jade has been recovered in substantial amounts from several of these localities. Many dense, fine-grained, green-colored rocks have mistakenly been called jade; but, from a gemological point of view, jade is a name given to the massive, gem-quality varieties of the two rock-forming minerals nephrite and jadeite. Nephrite is an amphibole, a silicate of calcium and magnesium that usually contains a small amount of iron. Jadeite, on the other hand, is a pyroxene and is a silicate of sodium and aluminum; usually, however, it contains variable amounts of two other pyroxene minerals, diopside (silicate of calcium and magnesium) and acmite (silicate of sodium and iron), which, when present in sufficient amounts, produce a dark green variety of jade called chloromelanite. It is true that nephrite and jadeite resemble each other very closely, but they can be distinguished by their different physical and chemical properties. Not only is jadeite harder than nephrite but it has a higher specific gravity. In general, the specific gravity of jadeite is 3.32 and that of nephrite is 2.98. Both of these minerals have a wide range of colors and color shades. Jade ranges in color from pure white, through every possible shade of green to amethyst, mauve, violet and light blue, yellow, orange and diverse tints of brown, red, and black. Because the colors in nephrite and jadeite usually are distributed unevenly, descriptive terms such as mutton fat, spinach green, and onion green have been employed to describe jade. Successful use of jadeite or nephrite as gem quality jade depends upon several important properties, such as desirable color, color pattern, and a certain degree of translucency. Because of this, the amount of jadeite and nephrite that is of gem quality is rather small in comparison to the amounts of these materials that are of mineralogical significance only. The occurrences of nephrite and jadeite, especially nephrite, are comparatively widespread and common in California. Most deposits of these interesting gemstone materials have been found only in or adjacent to bodies of serpentine, an association that seems to be characteristic of nephrite and jadeite occurrences throughout the world. Exceptions to this, however, are the unusual occurrences of nephrite associated with magnetite, epidote, chlorite and garnet in irregular contact metamorphic zones between granitic rocks and dolomitic limestone, near Victorville in San Bernardino County and in the western part of the Eagle Mountains in Riverside County. Many of the occurrences of nephrite and jadeite in California are well known to individuals and groups of amateur mineralogists but the several reports that follow, which have been prepared and published by the Division of Mines and Geology, describe in detail a few of the best known and most significant occurrences of nephrite and jadeite in California.

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

The Jaguar’s Children: Pre-Classic Central Mexico has as its subject one of the most arresting topics of New World prehistory. The Olmec of Mexico—originators of the earliest great civilization in Middle America—produced an extraordinary art. Its impact on contemporary and subsequent Mexican developments was enormous. It is this impact on an area in the Central Highlands, parts of the states of Morelos, Puebla, and the Valley of Mexico, that is described here by Michael D. Coe of Yale University. Long a student of the Olmec era, Dr. Coe discusses the extensive site of Tlatilco, the transitional site of Tlapacoya, and the very important and previously unpublished site of Las Bocas. Problems of symbolism, iconography, and the close relation of Olmec art to religion are examined, as well as the relation of Olmec culture to that of Central Highland tradition. Illustrated by over 200 pieces, many published for the first time, the emphasis has been placed on material from Las Bocas. The most important “baby-face” figures of the period have come from that site. These are graphic and humanized representations of the major Olmec deity, a rain god whose shape was that of a were-jaguar, a fat, childlike creature with feline features. Believed to have been born of a jaguar father and a human mother, they are the Jaguar’s Children. Dr. Coe first published on Pre-Classic Middle America and the Olmec in 1957 and is the author of the important articles on them in the Handbook of Middle American Indians. His excavations at the early village site of La Victoria on the Pacific coast of Guatemala were reported in the Papers of the Peabody Museum of Archaeology and Ethnology, Harvard University (1961). He wrote the volume on Mexico (1962) in Praeger’s Ancient Peoples and Places series and was engaged in a work on the Maya to appear in the same series.

gems, jade, fei cui, pyroxene jade, jadeite, amphibole jade, nephrite, dyed nephrite, dyed jade, dyed nephrite

Since we first encountered dyed jadeite in 1956, we have expected the appearance of dyed nephrite, but until recently we had not seen or heard of any. Figure 13 is a photograph of a well-carved nephrite tablet with chrome-green mottling. Spectroscopic examination of the green areas proved to us that the color is due to dye. Possibly, nephrite does not take the dye uniformly; therefore, this accounts for the absence of dyed material in the trade.

gems, gem testing, gemology, specific gravity, scales, weights, weighing

This unique survey of the history of weighting and its instruments, from the earliest known examples in the millennia before Christ to the modern era, is generously illustrated with 98 plates depicting scales, weights, and containers from the great collections of the world. It includes the known hallmarks of the scale and weight makers of Western Europe and lists of the weights of the world and their metric equivalents, by country and by name of weight. [RWH: Like most Western works, this book completely ignores the tremendous work done by Arabic-language scholars like al-Bīrūnī and al-Khazinī, who were measuring specific gravity hundreds of years before European scholars.]

jade, nephrite, treatments, dyed jade, gems

Liddicoat reports the identification of dyed nephrite jade at the Gem Trade Laboratory in Los Angeles, describing a carved tablet whose green coloration was established by spectroscopic examination to be artificial. The observation follows an interval during which dyed jadeite was already known to the laboratory but comparable treatment of nephrite had remained unconfirmed in its experience. The author states that dyed jadeite was first encountered in 1956 and that the subsequent appearance of dyed nephrite had therefore been anticipated. Until the specimen described in this note was examined, however, the laboratory had neither seen nor heard of such material. The object is characterized as a well-carved nephrite tablet with chrome-green mottling and is illustrated in a photograph showing its ornamental openwork design. The description of its colour records the visual appearance of the green patches; the note attributes their coloration to dye on the basis of spectroscopy. Examination specifically targeted the green areas, linking the identification of treatment to the coloured portions of the carving. Although the spectroscopic conclusion is stated unequivocally, no absorption wavelengths, spectral illustration, instrumental details, or comparison with untreated nephrite are supplied. The account likewise provides no information about the tablet’s geographical origin, the identity of the colouring substance, the method of application, or the depth and durability of the treatment. Liddicoat suggests that nephrite may not take dye uniformly and offers this as a possible explanation for the previous absence of dyed nephrite from the trade. This explanation remains tentative rather than an experimentally demonstrated property of the material. The report thus combines a definite identification of artificial coloration in an individual nephrite carving with a cautious suggestion concerning the practical limitations of dyeing nephrite. Its principal contribution is to document the laboratory’s encounter with a treatment it had expected following the recognition of dyed jadeite, while identifying spectroscopy as the means by which the artificial origin of the specimen’s green coloration was established.

Burma, jade, gems

Further investigation of maw-sit-sit, a vivid green ornamental stone from northern Burma, identifies its colouring constituent as a chromium-rich alkali pyroxene dispersed through a predominantly albite groundmass and leads to the proposed descriptive name jade-albite. Earlier examination had established the rock’s albite-rich composition but failed to identify the extremely small green pigment grains because they could not be adequately separated for chemical or X-ray analysis. Electron microprobe examination of a polished specimen demonstrates that chromium and iron are concentrated in the pigment rather than the surrounding albite. The reported chromium-to-iron ratio is approximately 3:1, with silicon also abundant and smaller quantities of titanium, calcium, and potassium detected. The article explains the principles and capabilities of electron-probe analysis, emphasizing its value for examining minute constituents in heterogeneous rocks. Although the initial measurements narrow the identification to a chromium-bearing pyroxene related to jadeite or aegirine, the grains remain too small for a satisfactory quantitative analysis. Improved concentration is achieved by grinding the rock to particles smaller than 10 micrometres and centrifuging them in a heavy-liquid mixture with a density of 2.75. The resulting sediment is substantially greener than either the original material or the lighter fraction. Comparative X-ray powder diffraction places the pigment within the alkali-pyroxene group, with lattice spacings intermediate between those of jadeite and aegirine. Partial chemical analysis of an approximately 70 per cent pigment concentrate yields about 10 per cent Na₂O, 7 per cent Cr₂O₃, and 4 per cent Fe₂O₃. Allowing for residual albite and possible iron contamination during preparation, Gübelin estimates that the pigment contains approximately 10 per cent Cr₂O₃ and constitutes roughly 20–25 per cent of the rock. He interprets it as jadeite in which substantial aluminium is replaced by chromium and iron, represented approximately by Na(Al,Cr,Fe)Si₂O₆, and proposes the name chrome-jadeite. Complete chemical characterization remains unattained because the minute, intimately intergrown crystals cannot be isolated in sufficient purity. The nomenclatural conclusion distinguishes the composite ornamental rock from jadeite itself, chloromelanite, and epidote: its dominant constituent is albite, while its striking colour arises from disseminated chrome-jadeite. Jade-albite is therefore recommended as a mineralogically informative designation, with maw-sit-sit retained as an acceptable local name.

corundum, Montana.12, USA.12, gems

Lab notes - NY. Note on 10 ct. stone (with photograph). Probably not Yogo (as it has rutile silk)