corundum, treatments.6, gems

gems, Ceylon, Sri Lanka, scapolite, composition

A study of the composition of gem scapolites. Additional abstract: Dunn, Nelen and Norberg examine gem scapolites in terms of the marialite–meionite solid-solution series, relating composition to gemological identification. They distinguish Na-dominant marialite from Ca-dominant meionite and discuss compositional variation in gem material.

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

This volume contains many of the papers presented at the Dumbarton Oaks conference on falsifications and misreconstructions of Pre-Columbian art, organized by Elizabeth P. Benson and held on October 14th and 15th, 1978. The purpose of the conference, and thus this volume, was to raise the issue of Pre-Columbian forgeries. A surprising number of falsified or largely reconstructed objects do exist in public and private collections and, in the case of architecture, in the public domain; many have been published in the literature as representative of Pre-Columbian artistic forms. The danger is that these recreations, unless identified as such, can distort our understanding of Pre-Columbian art and can lead to erroneous stylistic and iconographic interpretations. Thus the papers in this volume note the range of “antiquities” produced in relatively modern times, suggest why these were and still are being created, and show how such forgeries can be detected. In his 1964 article, “The Problem of Fakes in Pre-Columbian Art” (Curator 7: 19–32), Gordon Ekholm mentioned most of the published studies pertaining to Pre-Columbian forgeries. These studies need not be reviewed again here, but it is clear that the subject has been sparsely treated. Yet forgeries have a considerable time depth. Ekholm noted that fakes created as early as the 1820s in Mexico were of concern to such scholars as W. H. Holmes, Francisco Plancarte, and Leopoldo Batres near the turn of the century. Esther Pasztory, in this volume, discusses the Mexican falsifications of the nineteenth century in greater depth and argues strongly for a reappraisal of some well-known pieces acquired during this period. It would seem that one can no longer argue for the validity of an object solely because it has a known history of some 150 years.

gems, ancient gemology, early gemology, ancient mineralogy, early trade, ancient history, lapis lazuli, China, Rome

Ferguson examines contacts between China and the Roman world, bringing together classical and Chinese evidence for knowledge of one another and for the movement of goods across the long-distance trade routes linking the Mediterranean, Central Asia, India, and China. He discusses geographical knowledge, diplomatic contacts, and commerce, including the transmission of luxury commodities, and considers the limitations of the literary evidence for direct Sino-Roman relations. The study is relevant to the history of the gemstone and luxury trade because it places precious materials within the broader exchange of high-value goods between East and West during the Roman period.

corundum, USA.12, North Carolina.12, gems

A practical guide to North Carolina’s mineral and gemstone collecting localities, combining introductory gemology with a county-by-county directory of occurrences. Preliminary sections review gemstone history, physical and optical properties, cutting and polishing, color modification, and synthetic, imitation, and assembled stones. An account of the state’s gem-mining history introduces its principal gem materials, including diamond, ruby, sapphire, emerald, aquamarine, hiddenite, garnet, rutile, and quartz varieties. Locality descriptions identify minerals and associations, give directions and historical information, and refer readers to fifty accompanying maps. Particular attention is given to the emerald and hiddenite deposits of Alexander County, the ruby and sapphire workings around Franklin and Cowee Valley, and the pegmatites of the Spruce Pine district. Appendices list museums, mineral dealers, and collecting clubs, and summarize identifying properties of minerals from the Franklin and Spruce Pine areas. Color photographs illustrate representative specimens. Compiled principally from earlier publications and information supplied by collectors, with limited field checking, the circular documents collecting opportunities and locality knowledge at the time of publication. It also discusses equipment, specimen labeling, landowner permission, responsible collecting, and hazards around mines and excavations.

gems, jade, nephrite, Taiwan, nephrite cat’s eye

Two samples of Taiwan's jade, one of them with a clear cat's-eye effect, have been studied by optical, x-ray, thermal and electron microprobe analyses and SEM investigations. They showed that both samples are tremolitic members of the tremolite-actinolite- ferroactinolite series, with identical chemical and mineralogical composition. The diverse shades of green colour and cat's-eye effect are related to different arrangements of the fibres.

gems, jade, nephrite, Taiwan, amphibole jade, jade cat’s eye, tremolite cat’s eye

The Taiwan Cat's-Eye"is a tremolite cat's-eye. The gem material, cat's-eye tremolite occurs as veins at the contacts of graphite-sericite schist and serpentinite sills in association with nephrite, asbestus, talc and diopside-dominant skarn in the Fengtien area, south of Hualien. It is greenish yellow, pale yellow, honey yellow, green, rarely dark green, dark brown or black in color; translucent to opaque. H. 6-7, G. 3.045. Under the microscope, cat's-eye tremolite is colorless or pale green in color, consisting solely of fine, long sub-parallel fibers of tremolite in contrast to nephrite. Twisting or bending and wavy extinction are common. c∧Z' 0゜-10゜. α 1.613, β 1.626, γ 1.637; γ-α 0.24. The X-ray data are very similar to those of tremolite from St. Gotthard, Switzerland. Four chemical analyses reveal no marked differences in composition between the varieties of different colors, showing about 10% of the ferro-actinolite molecule. Some gemological features are also given. Diopside shows more crystal forms than previously reported, and the occurrence of grossularite is limited to diopside-grossularite veins near the contacts. Minor uvarovite and vesuvianite were first found in Taiwan. The former occuring as minute inclusions in diopside has n l. 778 and a_0 11.87A, corresponding to uvarovite with 10% Cr_2O_3. The latter of small prismatic crystals shows similarity in X-ray data to vesuvianite from Canzoccoli, Italy. The mineralization of the Fengtien nephrite-asbestus deposits may be divided into two stages : skarn formation and ore deposition, which might have taken place during serpentinitization by hydrothermal solutions rich in silica and lime. Cat's-eye tremolite was formed evidently later than nephrite."

gems, euclase

E.J. Gübelin describes a sapphire-blue variety of euclase from the Miami district near Karoi, Zimbabwe, then Rhodesia. Previously reported euclase from the district was colorless, pale blue, or light green. The dark blue material was traced to a locality about 5 miles southwest of Miami, near the southwestern edge of a beryl- and muscovite-bearing gneiss shield. Gübelin proposed that euclase formed as a secondary mineral when beryl broke down during the cooling of the region’s pegmatites, at approximately 400–600 °C. Of the 33 rectangular and square faceted stones examined, only a few appeared uniformly dark blue. Most showed alternating dark blue and colorless zones. Electron microprobe measurements gave iron contents equivalent to 0.12% Fe₂O₃ in the dark blue portions and 0.06% in the colorless portions. Gübelin attributed the sapphire-blue color to ferric iron and suggested that color centers might also contribute. Spectrophotometry showed an absorption minimum at 465 nm and a slight shoulder near 570 nm. The specimens were inert under both long-wave and short-wave ultraviolet light. Measurements on the 12 largest stones gave refractive indices spanning 1.652–1.672 and a consistent birefringence of 0.019. The stones showed pronounced pleochroism in azure blue, Prussian blue, and greenish blue. The reported hardness was 7½ and the specific gravity ranged from 3.06 to 3.13. X-ray diffraction data from five Gandolfi patterns agreed closely with published values for monoclinic euclase and confirmed the identification. Under magnification, even apparently uniform blue stones showed cloudy or zoned color distributions resembling those of some blue sapphires. The colorless portions were nearly inclusion-free, while blue portions commonly contained fractures, including partially healed cracks with irregular liquid inclusions and open cracks that produced bright reflections as the stones moved. Gübelin observed no mineral inclusions and found the fracture patterns insufficient to establish the material’s identity or geographic origin. The resemblance to sapphire underscored the importance of optical and crystallographic measurements in identifying the new color variety.

corundum, synthetic corundum.7, Verneuil, Czochralski, pulling, flux, hydrothermal, gems

Crystal growth techniques are reviewed through the physical principles that govern growth rate, composition, crystal quality, and process control. Single crystals are distinguished from polycrystalline solids by the continuity of atomic order, which makes them important for measuring material properties and producing devices such as lasers and oscillators. The account emphasizes that imperfections are unavoidable and can influence growth beneficially as well as adversely. Temperature and concentration gradients provide the principal driving forces for transporting material to the growth interface and removing latent heat. Rough interfaces offer numerous incorporation sites, whereas smooth crystal faces grow by the lateral spreading of layers, often sustained by defects such as spiral sources. Control of temperature, fluid motion, growth rate, and seed orientation is therefore central to obtaining useful crystals. Impurity accumulation ahead of an advancing interface can produce constitutional supercooling, destabilizing the interface and generating cellular or dendritic structures and inclusions. Dopant incorporation is related to segregation behavior, diffusion, growth rate, and the boundary layer, explaining how thermal and hydrodynamic fluctuations can create compositional variations. A classification based on solid, liquid, and vapor transformations distinguishes batch from continuous processes and provides a framework for comparing techniques. Selection depends on melting behavior, solubility, volatility, chemical stability, and requirements for purity, orientation, size, and perfection. Directional freezing methods—Kyropoulos, Bridgman, and Czochralski pulling—are compared in terms of heat flow, motion, interface shape, and controllability. Solution methods encompass low-temperature aqueous or organic growth, high-temperature flux growth, and hydrothermal synthesis, with supersaturation generated by evaporation, cooling, or thermal-gradient transport. Their generally slower growth is balanced against their suitability for materials that cannot readily be grown from a melt. Other methods include gel growth, Verneuil flame fusion, zone crystallization, chemical vapor transport, and vapor–liquid–solid growth. The discussion connects Verneuil process fluctuations with bubbles, unfused powder, and dopant banding, while zone methods illustrate purification and controlled doping. Emerging developments include combined flux–vapor growth, edge-defined film-fed growth, liquid-phase epitaxy, crystallization within optical-fiber capillaries, and temperature oscillation to suppress unwanted nuclei. Processing under reduced gravity is considered promising but complicated by surface-tension effects. Throughout, the emphasis is on relationships between methods and the mechanisms limiting control, providing a basis for understanding technological developments rather than detailed manufacturing instructions.

gems, ancient mining, Europe, archaeology, archaeogemology

Our knowledge of the organization and life of the Roman mines in the Danubian provinces is strikingly incomplete considering the importance of the subject. Fresh finds and research, however, make the picture somewhat clearer; the following discussion concentrates on several points which, studied primarily on the basis of written sources, allow of a certain progress. The main conclusion of the present study is that Roman mining in the Danubian provinces—and, no doubt, also elsewhere—was more of a system than is commonly thought. That branch of industry demanded special care which exceeded the means of an area or a province, as illustrated by the transportations of peregrini from Dalmatia to Moesia Superior and Dacia for compulsory work in the mines. The hard fact that metals, especially precious ones, were both rare and needed, naturally led to the relative centralization of the mining administration, and to a distinction between the provinces which were rich in minerals and those which were not. Conceivably, such a state of affairs must have had manifold consequences. One of them should be stressed: the gradual municipalization of the provincial territory, which is a process common to all the Empire, was bound to affect the countries of central Noricum, southern Pannonia, northern Dalmatia, and almost the whole of Moesia Superior in a far lower degree, owing to the occurrence of mines within the vast fiscal domains. This had a bearing on all aspects of life there, notably on the organization of the portorium and on the degree of Romanization of the indigenous population.