gems, ancient gemology, early gemology, ancient mineralogy, early trade, India

Magadha was a region and kingdom in ancient India, based in the eastern Ganges Plain. It was one of the sixteen Mahajanapadas during the Second Urbanization period. The region was ruled by several dynasties, which overshadowed, conquered, and incorporated the other Mahajanapadas. Magadha played an important role in the development of Jainism and Buddhism and formed the core of the Maurya Empire (ca. 320–185 BCE).

corundum, color.4, gems

Richard H. Bube’s Photoconductivity of Solids is a comprehensive treatment of the physical principles, experimental investigations, preparation methods, and practical applications of photoconducting materials. Written for graduate students and researchers in solid-state physics, chemistry, and related fields, the book examines the increase in electrical conductivity that occurs when solids absorb electromagnetic radiation, including infrared, visible, ultraviolet, X-rays, and gamma rays. Beginning with Willoughby Smith’s discovery of the photoconductivity of selenium in 1873, Bube traces the historical development of the subject and the growing understanding of electronic processes in semiconductors and insulators. The theoretical discussion introduces crystal structures, chemical bonding, electronic energy bands, forbidden energy gaps, charge-carrier mobility, and the influence of impurities and structural imperfections on electronic behavior. Particular emphasis is placed on the generation of electrons and holes by optical excitation, their transport through crystals, and the processes by which they become trapped or recombine. The author distinguishes intrinsic photoconductivity, arising from excitation across a material’s fundamental energy gap, from impurity or imperfection photoconductivity, in which localized electronic states associated with foreign atoms, vacancies, and other defects determine the absorption and electrical response. The treatment includes detailed consideration of carrier lifetimes, trapping centers, recombination kinetics, photoconductive gain, spectral sensitivity, electrode effects, and the influence of temperature, applied voltage, and illumination intensity. Separate chapters examine the preparation of photoconducting materials, including powders, sintered and evaporated films, chemically deposited layers, and single crystals grown by vapor-phase, melt, solution, and zone-melting techniques. These methods are discussed in relation to chemical purity, crystal perfection, impurity incorporation, and the reproducibility of electrical and optical properties. Particular attention is given to materials such as selenium, diamond, zinc sulfide, cadmium sulfide, cadmium selenide, lead sulfide, lead selenide, germanium, silicon, and the alkali halides. The discussion of crystal imperfections is especially relevant to the study of color centers, including F centers formed by electrons trapped at anion vacancies, whose characteristic optical absorption can be accompanied by photoconductivity. The relationship between absorption, luminescence, and photoconductivity is examined throughout, providing a physical framework for understanding how defects and impurities modify the optical and electronic properties of crystalline solids. Later chapters address energy-band transitions, excitons, charge-carrier scattering, trapping phenomena, recombination mechanisms, and theoretical models of photoconductivity. Related phenomena, including photovoltaic, photomagnetoelectric, surface photoelectric, photodielectric, and bombardment-induced effects, are also considered. An appendix surveys practical applications of photoconductors in radiation detectors, infrared sensing, television camera tubes, electrophotography, and other electronic devices. Extensive references, mathematical treatments, experimental data, tables, and diagrams support the discussion. Although primarily concerned with solid-state physics rather than gemology, the book provides important background for understanding electronic defects, color centers, optical absorption, and luminescence in minerals and gemstones, particularly where these phenomena arise from impurities and structural imperfections in crystals.

gems, agate, Germany, Idar-Oberstein, history, lapidary, fashioning

A firsthand account of Idar-Oberstein’s gemstone industry following its postwar recovery. Visits to Professor Schlossmacher’s gemological institute, the Gebrüder Leyser cutting establishment, and the Heinz brothers’ historic water-powered workshop document laboratory equipment, specialized cutting operations, and traditional agate-working methods. Photographs illustrate sawing, grinding, and polishing. The article also describes the town’s extensive network of cutters, dealers, and jewelry manufacturers, its international rough supplies, and difficulties recruiting skilled workers and attracting younger people to the craft.

gems, leucite

gems, gemology, advanced gemology, gem testing, x-ray powder diffraction, analytical

Instruction in the various laboratory methods for investigating crystals has long been part of the mineralogy and geology curriculum at the Massachusetts Institute of Technology, encompassing both optical and x-ray techniques. While suitable texts exist for optical methods, there has been no adequate textbook on the x-ray powder method. To support lectures and prepare students for laboratory work, the authors initially wrote a set of notes on the theory and practice of this method, which eventually evolved into this book. The expanded format allowed for more detailed discussion and the inclusion of advanced material beyond what could be covered in a short course. The powder method is inherently simple yet widely valuable across science and industry, often used by individuals with no formal training in crystallography. This book is written with such users in mind, maintaining a fundamental approach while assuming only limited prior knowledge. It omits detailed coverage of general crystallography, x-ray generation, and equipment beyond powder cameras, as these are addressed in other sources. Detection methods using photographic film are emphasized, given their simplicity and permanence, despite the growing use of ionization-type detectors. The principles outlined apply regardless of detection technique, but film is expected to remain relevant in routine applications for the foreseeable future.

gems, corundum, History.1, Indian gemology, Indian mineralogy, history of gemology, history of mineralogy, Indian lapidary

This small volume brings together two Sanskrit treatises on the traditional Indian examination of gemstones, one extracted from the Smṛtisāroddhāra and the other attributed to Īśvaradīkṣita, with the Sanskrit text in Devanagari accompanied by a Tamil translation by K. S. Subramanya Sastri. The works belong to the Indian ratna-parīkṣā tradition, in which precious stones are classified and assessed according to their appearance, physical characteristics, desirable qualities, defects, provenance, and suitability for use. Attention is given to the recognition and valuation of gems and to traditional ideas concerning the beneficial or harmful effects associated with stones of particular qualities. The volume is valuable for preserving relatively short Sanskrit sources on practical gem knowledge and for illustrating the close relationship in traditional Indian gemology between observation and commercial evaluation on the one hand and religious, astrological, and cultural concepts on the other. The two texts were originally issued in 1958 in the journal of the Tanjore Maharaja Serfoji’s Sarasvati Mahal Library.

Zimbabwe, Rhodesia, gems

Gübelin examines emeralds from the newly discovered Sandawana deposits in the Belingwe area of present-day Zimbabwe, combining an account of their discovery and geological setting with measurements and microscopic observations intended to establish distinguishing characteristics. Laurence Contat and Cornelius Oosthuizen encountered emerald while prospecting for pegmatite minerals, with an initial discovery in October 1955 followed by a significant deposit found in May 1957. The emeralds occur in association with tremolite schists and pegmatite dikes in the Mweza Range, a setting compared with that of emeralds from Austria’s Habachtal. Geological knowledge remained preliminary, and the workings were still limited, although emerald-bearing material derived from erosion was also recognized. An initial lot of ninety-two emeralds was submitted for investigation. The faceted specimens described are small, weighing 0.15–0.38 carat, but display vivid, comparatively uniform green color with a warm yellow component that remains strong even at these sizes. A reported chemical analysis includes chromium, iron, magnesium, sodium, and lithium in addition to the principal constituents of beryl. Measured optical properties are relatively high for emerald, with representative refractive indices of approximately 1.593 and 1.586 and birefringence near 0.007. Specific gravity ranges from 2.744 to 2.768. Most specimens show the familiar emerald absorption spectrum, a weak red appearance through the Chelsea filter, and distinct bluish-green and yellowish-green dichroic colors. They are inert under the long-wave and short-wave ultraviolet radiation used in the study, with ultraviolet transmission ending near 320 nm. Because these properties overlap those of emeralds from other deposits, Gübelin places particular emphasis on inclusions. The most characteristic assemblage consists of fine tremolite needles approaching actinolite in composition, occurring as short scattered rods and long, slender, sometimes curved fibers. Tiny disk-like fissures along some needles create the appearance of flakes pierced by rods. Compared with Habachtal material, Sandawana emeralds contain finer needles, less densely grouped, with short rods accompanying the longer fibers. Other observed inclusions include brown garnet, limonite coatings and fracture fillings, and rare altered plagioclase, magnetite, and hematite. Dust-like green or brown patches, described as splashes, may form halos around resorbed garnets; an illustration identifies such formations as comprising extremely minute liquid droplets. Additional fissures form interrupted lines and bands parallel to the basal plane, differing in appearance from the more extensive layers of disk-like fissures described in Russian emeralds. Gübelin concludes that the combination of physical properties, tremolite morphology, internal irregularities, and vivid color provides a practical basis for recognizing Sandawana emeralds, while emphasizing the importance of direct observational experience.

gems, corundum, properties.3, synthetic corundum.7, spinel, chrysoberyl, quartz, tourmaline, zircon, scapolite, spinel inclusions

W.F. Eppler examines the inclusions responsible for asterism in spinel and chatoyancy in chrysoberyl, quartz, tourmaline, zircon, and scapolite, emphasizing the need to distinguish solid crystals from apparently similar hollow channels and to assess whether inclusions were trapped during growth or formed subsequently by exsolution. In natural spinel, oriented rutile needles following octahedral edges provide one explanation for asterism, but other fibrous inclusions remain unidentified. Sphene crystals in Ceylon spinel illustrate the distinction between relatively large primary crystals enclosed during host growth and minute needles attributed to exsolution. Partial dissolution and the arrangement of larger crystals on former growth planes support their primary origin, whereas their sparse distribution prevents them from producing a star. Burmese spinels contain additional unidentified dark crystals and minute brownish particles tentatively interpreted as rutile; patterned concentrations around larger inclusions suggest localized strain may influence exsolution. Experiments with synthetic spinel show that heat-induced separation of excess alumina can generate oriented plates and weak asterism, but the resulting effects lack commercial value. Elongated gas inclusions can also produce a four-rayed star in suitably oriented cabochons. Examination of a sharply chatoyant chrysoberyl reveals short, birefringent needles with a refractive index higher than the host, contradicting an explanation based exclusively on hollow channels for that specimen. Their identity and origin remain uncertain, although exsolution is suggested. Similarly, inclusions in a rose-coloured tourmaline that resemble channels in reflected light prove in transmitted light to be brown, birefringent crystal fibres with a higher refractive index than tourmaline. Eppler interprets these as primary inclusions formed alongside the host. Quartz cat’s-eye and tiger’s-eye are discussed in terms of aligned amphibole-asbestos fibres, while an earlier observation of zircon chatoyancy is attributed to unidentified minute crystals parallel to its principal axis. Madagascar scapolite displays a combination of hollow and liquid-filled channels, crystalline needles, and oriented blades, all potentially contributing to its cat’s-eye effect. The blades are interpreted as products of exsolution within the marialite–meionite series. Photomicrographs demonstrate that similar optical phenomena can arise from inclusions differing in composition, physical state, morphology, and developmental history, making detailed optical examination essential to explaining individual specimens.

jade, jadeite, fei cui, nephrite, nomenclature, gems

J.J. Reed clarifies the mineralogical distinctions underlying the terms greenstone, nephrite, bowenite, and jade, responding to uncertainty in their application to Māori artefacts. He explains that the materials commonly grouped together as Māori greenstone include two compositionally distinct substances. Nephrite consists essentially of amphibole belonging to the tremolite–actinolite series, whereas bowenite consists essentially of serpentine. Jadeite, a sodium aluminium pyroxene, is mineralogically distinct from both. These differences make the customary group terms unsuitable as substitutes for precise material identification. In strict gemmological usage, jade encompasses nephrite and jadeite alone; bowenite therefore falls outside its definition. Greenstone, as applied to Māori objects, covers both nephrite and bowenite, so the two collective terms overlap without being synonymous. Reed notes that pounamu and tangiwai are generally considered the Māori names for nephrite and bowenite, respectively, while leaving the interpretation and acceptance of broader ethnological terminology to ethnologists. He recognizes a practical need for a collective expression covering jadelike artefacts regardless of their mineralogical composition. Although a broader definition of jade might have served this purpose, its established restriction to nephrite and jadeite makes descriptions that include bowenite under “Māori jade” misleading. “Māori greenstone” offers a suitable alternative if greenstone is accepted in the inclusive sense proposed. Examples from European archaeological writing demonstrate that greenstone has also been used outside New Zealand for jadeite and other materials, supporting its potential as a general descriptive category rather than a designation confined to particular minerals. Reed suggests that the term would presumably have encompassed jadeite in New Zealand had that mineral occurred there and been used by Māori. His recommendation combines broad classification with explicit identification: scientific descriptions should employ nephrite, jadeite, or bowenite whenever the material is known, while an inclusive archaeological designation can retain the specific identification in parentheses, as in “greenstone (nephrite).” The note thus proposes a terminological framework that accommodates established ethnological usage while preserving the mineralogical distinctions necessary for accurate descriptions and comparisons of artefacts.

inclusions, microscopy, gems

Gübelin explains the principles of phase-contrast microscopy and describes equipment adapted to examining inclusions and subtle internal structures in gemstones. Developed from F. Zernike’s work, the method converts differences in the phase of transmitted light, arising from variations in thickness or refractive index, into visible differences in brightness. It thereby reveals transparent features that produce insufficient contrast under ordinary bright-field illumination. Closing the condenser aperture or defocusing can improve conventional contrast but reduces resolving power, while dark-field illumination chiefly emphasizes sharp boundaries and may inadequately display gradual transitions or details within inclusions. Phase contrast employs an annular illuminating diaphragm and a corresponding phase plate in the objective to modify the relationship between direct and diffracted light. Positive phase contrast renders optically denser features darker than their surroundings, whereas negative phase contrast reverses this relationship. Conventional equipment initially presented difficulties because its high-power objectives had insufficient working distance and depth of focus for inclusions situated within relatively thick gemstones. With assistance from H. Piller of Zeiss-Winkel, Gübelin obtained a specially designed arrangement incorporating suitable illumination components, annular diaphragms, and objectives of lower magnification with longer working distances. An auxiliary microscope permits alignment of the illuminating ring and the objective’s phase ring. The arrangement allows convenient changes between phase contrast and conventional illumination, facilitating comparison and interpretation of the same features. Its principal value lies in increasing the visibility of inclusions and compositional irregularities, rather than providing quantitative refractive-index measurements. Comparative examples include muscovite flakes in yellow beryl from Madagascar, structures in a Colombian emerald attributed to incomplete calcite exsolution, alteration to pinite in Sri Lankan iolite, and partly healed fissures in sapphire, fluorite, and beryl. Phase contrast makes the boundaries and internal details of muscovite conspicuous despite its small refractive-index difference from beryl. It also distinguishes residual liquid-filled portions of healed fractures from the surrounding healed material and can reveal gas bubbles within those residual cavities. Structural irregularities and zoning may become visible as contrasting light and dark areas where exsolution, precipitation, alteration, or healing has produced slight local differences in refractive index. Gübelin emphasizes that the method is most useful when optical differences are small and the relevant structures sufficiently thin. It offers little advantage for many ordinary inclusions whose refractive indices differ greatly from those of their hosts, and it does not reveal strain or deformation caused by stress. The article presents phase contrast as a valuable addition to gemological microscopy for investigating internal heterogeneity and interpreting processes recorded within gemstones.