corundum, synthetic corundum.7, gems

Gübelin describes the diagnostic characteristics of the newer flux-grown synthetic rubies produced by Chatham, Kashan and Knischka. Particular emphasis is placed on microscopic examination of their characteristic inclusions, some of which may resemble features encountered in natural ruby and therefore complicate identification. The article illustrates and compares the internal features of the three products, showing how inclusion morphology and growth-related characteristics can be used to distinguish these synthetic rubies from natural stones. The paper contains 42 figures, 41 in color.

corundum, synthetic corundum.7, flux, Knischka, gems

Gunawardene examines the gemmological and crystallographic characteristics of the newly developed Knischka synthetic ruby, produced by Paul Otto Knischka of Austria using a modified gradient-transport technique involving supercooling and supersaturation. The paper describes the unusual crystal morphology of the material, including the development of numerous additional crystal faces, and compares these forms with those of natural corundum. Particular attention is given to microscopic identification. Characteristic internal features include turbid clouds, swirls of colour, liquid or feather-like patterns, negative crystals associated with elongated crystalline tubes, metallic platelets, melt residues and two-phase inclusions. Although some inclusions can resemble features in natural ruby or other synthetic rubies, their morphology and associations provide useful criteria for recognizing Knischka material. The study emphasizes microscopy as the principal means of identification and illustrates the diagnostic inclusions and crystal-growth features in detail.

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

Duyk describes an unusual 51 ct sapphire cabochon, apparently from Sri Lanka, containing two conspicuous internal cavities with well-developed crystalline outlines. He examines the morphology and optical appearance of these voids and discusses their relationship to the host sapphire, illustrating the features with nine photographs. The observations show that apparently empty, crystallographically shaped cavities can occur as internal features in natural sapphire and may provide useful evidence concerning the stone’s growth history.

tourmaline, cat’s eye, gems

The causes of chatoyancy in tourmaline are investigated through examination of twenty-two specimens representing different colours, localities and types of elongated inclusion. Polished slabs and cat’s-eye cabochons from Brazil, the United States and Mozambique were studied by optical microscopy, X-ray powder diffraction, electron-microprobe analysis and heating-stage observation of fluid inclusions. The host crystals were assigned principally to elbaite, with fewer dravitic specimens, using unit-cell parameters because conventional refractive-index and density measurements proved insufficiently reliable in the inclusion-rich material. No close relationship was established between tourmaline colour and this structural classification. Three main inclusion types are distinguished: irregular thread-like trichites, growth tubes and solid needles. Trichites commonly contain two-phase fluids and occupy healed fractures, but their variable orientation prevents them from generating a coherent cat’s-eye effect. Chatoyancy instead arises from densely distributed tubes or needles aligned parallel to the host’s principal growth direction. Growth tubes are interpreted as primary cavities associated with growth irregularities, strain or rapid crystallisation, whereas needles are elongated crystalline inclusions incorporated during growth. Within the examined suite, tubes occur more frequently in green tourmalines, while needles predominate in pink-red and blue specimens; trichites show no comparable colour association. Microchemical analyses indicate that the most common solid material filling the tubes is tourmaline with a composition and minor-element pattern similar to those of its host. Less common fillings include prosopite and cookeite, together with iron oxides and sulphides. Opaque channel material is identified as pyrrhotite, while red-to-brown coatings and iron-rich yellow halos are attributed more tentatively to iron oxides or hydroxides. Most fine crystalline needles likewise have compositions matching tourmaline. Other straight rods are identified as epidote close to clinozoisite in composition. Columnar aggregates of subhexagonal muscovite plates are also described. Heating-stage behaviour of two-phase inclusions suggests water and carbon dioxide as principal constituents, supporting a hydrothermal setting, while several associated minerals are consistent with late pegmatitic or hydrothermal processes. The study concludes that tourmaline chatoyancy cannot be assigned to a single foreign mineral inclusion: both aligned growth channels with varied fillings and crystalline needles, commonly themselves tourmaline, can produce the effect.

gems, spinel, spinel inclusions, root-like inclusions

G.R. Crowningshield records unusual inclusion features observed during examination of natural pink and red spinels at the Gemological Institute of America’s New York laboratory. The note places these observations in the context of increasing consumer familiarity with pink and red spinel and their more frequent appearance in the gem trade, both locally and in East Asia. Several lots, together weighing hundreds of carats, provided the material examined. Among these collections, two stones attracted particular attention because their inclusions differed from the forms more commonly encountered in natural spinel. One contained branching, root-like inclusions whose appearance recalled features previously observed in diamond, another mineral of the cubic crystal system. Earlier published diamond observations are cited as visual comparisons, without establishing that the inclusions in the two host minerals have the same composition or origin. A second spinel contained a series of rounded, frosted-looking features likened to tennis balls. These are identified as negative crystals, despite their superficial resemblance to gas bubbles in slag glass. The comparison concerns their microscopic appearance rather than an identification of the spinel as glass or of the cavities as ordinary gas bubbles. A third illustration provides a contrast by showing more familiar inclusions, including octahedral forms, in a red spinel. Three photomicrographs accompany the account: root-like inclusions photographed with dark-field illumination at 20× magnification, rounded negative crystals at 30×, and common natural-spinel inclusions, also at 30×. Together, the images document both unusual branching structures and rounded cavities alongside the more recognisable octahedral forms. The report is descriptive and does not assign a mineral species to the root-like inclusions, specify the contents of the negative crystals, or propose a formation mechanism for either unusual feature. Its principal contribution is to broaden the documented range of inclusion appearances in natural spinel and to distinguish the observed negative crystals from the bubble-like features they visually resemble.

synthetic beryl, emerald, natural beryl, emerald, gems

Electron-microprobe analysis is investigated as an additional means of distinguishing natural from synthetic emerald when conventional gemmological properties and internal features are inconclusive. Refractive indices, birefringence, specific gravity and fluorescence can overlap, while inclusions and growth structures may be absent or difficult to interpret. The study therefore examines differences in minor-element chemistry, contrasting the relatively near-ideal beryl composition of many synthetic emeralds with the greater chemical substitution commonly found in natural material. Forty-five faceted stones from different natural sources and synthetic manufacturers were examined, with four point analyses performed on each specimen. Magnesium and sodium provide the clearest separation within the investigated population. Natural emeralds contained at least approximately 0.8 wt% MgO, with most values between 1.5 and 3.0 wt%, whereas synthetic specimens commonly contained around 0.1 wt% and reached approximately 0.4 wt%. Natural stones contained at least 0.4 wt% Na₂O, while most synthetic stones had no measurable sodium; the highest reported synthetic value was 0.2 wt% in a Lechleitner sandwich product. Chromium and iron concentrations overlap between the groups and consequently do not provide a general diagnostic separation. Compositional variations among natural emeralds also show patterns associated with different geographic sources, with Colombian specimens tending to contain fewer impurities than most other natural samples. A Brazilian stone labelled as emerald from Conquista contained vanadium and iron but no detectable chromium, illustrating the variability of the colouring constituents. Additional observations include 0.3–0.4 wt% chlorine in Linde hydrothermal synthetic emeralds and exceptionally high chromium concentrations in Lechleitner synthetic emerald overgrowths. The author relates the characteristic network of fissures in these coatings to lattice-dimensional differences caused by chromium substituting for aluminium. Electron-microprobe analysis is presented as a means of obtaining diagnostic chemical information from cut stones without destructive sampling. However, the author explicitly recognizes that 45 stones cannot represent the full compositional range of either natural or synthetic emerald. The magnesium–sodium distinction is therefore proposed as a useful supplementary criterion requiring broader testing, including examination of new synthetic products. Water content and additional trace elements are identified as potentially valuable future discriminants.

corundum, inclusions.5, gems

Pinpoint illumination uses a highly flexible but extremely durable glass fiber-optic bundle that incorporates six easily interchangeable light wands of various shapes and cross-sectional thicknesses down to one millimeter in diameter. The wands are hand held and can be used to illuminate hard-to-reach areas in complex jewelry ino~intingsW. ith the pinpoint, ill~lmintaor, a gemstone can be examined from any angle; the light source is placed exactly where it is needed, minimizing glare and unwanted external or internal reflections.

peridot, St. John’s Island, Egypt, gems, Classical world, geology, inclusions

Hydrothermal origin of gem olivines from Zabargad Island (St. John), Red Sea, through the study of their inclusions. The conditions of deposit and nature of the fluid inclusions in olivine gems from Zabargad prove that all the minerals have crystallized by an hydrothermal process which affected the island's principal peridotite body. Circulations of hypersaline fluids at high temperature (750°-900°C) with abundant volatile elements (CO₂, N₂, Cl, S, H₂O), with low pressure (partial pressure of CO₂ between 0.4 to 0.8 kbar) caused mobilisation of the major elements contained in the peridotite ; the chemical composition of included minerals which appeared during the cooling of the brines demonstrates this. The same fluids as well as CO₂ satured silicate liquids, which chemical composition is similar to basaltic andesites, characterize « normal » olivines of peridotite. By comparison to fluid inclusions in olivines from Assab peridotite nodules (Erythrea), untouched by hydrothermal processes, we note, in olivines from Zabargad, the absence of carbonic fluids with high filling density (Assab pCO₂ = 7.5 to 8.3 kbar). Hydrothermal process responsible for olivine crystallization seems to be associated with whole tectonic and magmatic events connected with first stages of Red Sea opening.

gems, Arabic mineralogy, jewelry from the Middle East, ethnic jewelry

Development in the Kingdom of Saudi Arabia has progressed at an astonishing pace, and nowhere is this more evident than in the field of archaeology—an area the author argues holds the key to unlocking many of the mysteries surrounding Bedouin jewellery. In light of newly available information, the documentation and preservation of this cultural heritage is both timely and vital. *The Art of Bedouin Jewellery* by Heather Colyer Ross presents a clear and engaging exploration of the remarkable range of ornaments crafted not only for adornment but also as portable wealth. Beginning with a historical overview, Ross traces the diverse influences that have shaped this art form—from Vikings and Chinese artisans to ancient Etruscans and modern Asian cultures—while also offering a detailed look into the life and traditions of the Bedouin people, which give this jewellery its cultural context. With over 100 colour photographs, primarily taken by the author, the book serves as a comprehensive visual and textual catalogue of necklaces, bracelets, armlets, anklets, belts, headpieces, and more, found across the Arabian Peninsula. Regional styles, the silversmith’s techniques, and the materials used are thoroughly examined, and the inclusion of an extensive glossary and list of technical terms in both English and Arabic adds significant value. *The Art of Bedouin Jewellery* is not only a treasure trove for collectors, but also an indispensable resource for anyone seeking to understand the rich traditions and craftsmanship of Arabia.

corundum, synthetic corundum.7, gems

Single crystals of corundum attaining 5 cm across were synthesized from cryolite (Na₃AlF₆) flux by the seed rotation method. The effect of growth conditions such as growth temperature, temperature difference, baffle aperture, and rotation rate upon crystal perfection is discussed to clarify the optimum conditions required to obtain crystals of high quality, containing the minimum amount of flux inclusions. The external shape of the corundum crystals did not show a noticeable change, except that the edges became more rounded with an increase in rotation rate. Experiments to simulate convective flow in solution were carried out on two systems—water and water–saccharose—under conditions simulating those of flux growth. When a baffle plate with 20% aperture was used, the flow velocity reached a maximum.