corundum, chemistry.2, synthetic corundum.7, gems

Investigates the use of proton-induced X-ray emission (PIXE) to distinguish natural from synthetic ruby and assess relationships between trace-element composition and source. The study analyzes 160 specimens comprising 133 natural rubies from Afghanistan, Burma, two Indian localities, Kenya, Sri Lanka and Thailand, together with 27 synthetic rubies representing Chatham, Inamori, Kashan, Knischka, Ramaura, Seiko and an unidentified flame-fusion source. Some natural origins were supported by characteristic inclusions, whereas others depended on supplier information because the specimens were insufficiently transparent for microscopic verification. Measurements employed 2 MeV protons from a Van de Graaff accelerator, a silicon-lithium detector and a counting time of 150 seconds per specimen. Spectra were fitted using the AXIL program, with calibration standards enabling quantitative determination of trace-element concentrations relative to aluminum oxide. Natural rubies generally contained a greater variety and higher concentrations of impurities than synthetic specimens. Besides chromium, detected elements included silicon, chlorine, sulfur, potassium, calcium, titanium, vanadium, manganese, iron and gallium. Vanadium was undetectable in every synthetic specimen but occurred in most natural rubies, with exceptions among Thai and Indian samples. The detection limit was approximately 20 ppm in the absence of titanium. Burmese rubies had the highest mean vanadium concentration, with one specimen reaching 1800 ppm, while Thai rubies had the lowest mean. Consequently, detectable vanadium strongly supported natural origin within the studied population, although its absence did not establish synthetic origin. Most synthetic rubies contained little iron, with the Knischka specimen providing an exception; Thai rubies and some Sri Lankan specimens were comparatively iron-rich. Chromium concentrations varied considerably between groups but were relatively consistent within several individual sources, suggesting additional discriminatory value. The authors emphasize that source attribution requires combinations of elements rather than a single concentration. For example, high iron together with low chromium and vanadium favored a Sri Lankan attribution within their dataset. Titanium, calcium and potassium also offered potentially useful information in some cases. The results agree with published analyses obtained by energy-dispersive X-ray fluorescence and neutron activation. PIXE is presented as a rapid and useful identification technique, and the authors recommend developing a larger database of specimens with known origins. They nevertheless caution that synthetic ruby manufacturers could modify product compositions, potentially reducing the future reliability of distinctions based on trace-element chemistry.

corundum, sapphire, USA.12, Montana.12, inclusions.5, Dry Cottonwood Creek, gems

gems, inclusions, beryl, emerald, Australia, Norway

The second installment of Schwarz’s systematic study of the chemical properties of emeralds from different geographic sources, dealing with material from Australia and Norway. Norwegian specimens are from Eidsvoll near Lake Mjøsa, while the Australian material represents several occurrences, including Pilangoora, Wodgina, Calvert White Quartz Hill, Warda Warra, Melville, Torrington, Emmaville and Menzies. Chemical analyses are used to compare major and trace-element compositions and to evaluate variations among deposits and against previously studied Brazilian emeralds. Schwarz notes, among other distinctions, generally lower magnesium contents than in Brazilian material. The paper demonstrates the usefulness of chemical composition, considered together with gemological properties, for characterizing emeralds and assessing their geographic origin.

corundum, treatments.6, agate, chalcedony, dying, gems

corundum, quality.10, gems

An illustrated introduction to mineralogy and gemstones, drawing chiefly on specimens in the Smithsonian Institution’s National Museum of Natural History. White explains how chemical composition and atomic structure distinguish minerals, how they form in different geological environments, and how crystallization produces varied shapes, intergrowths, inclusions, and replacements. Sections on physical and optical properties, classification, mineral groups, modern analytical methods, and collecting establish a foundation for understanding the specimens illustrated. The gemstone chapters discuss discovery, mining, cutting, and polishing, followed by accounts of diamond, ruby and sapphire, beryl, opal, quartz, garnet, jade, and less familiar gem materials. Decorative stones and organic gems, including pearls, coral, and amber, broaden the coverage beyond transparent faceted stones. Gem nomenclature, color modification, laboratory-grown crystals, imitations, and assembled stones are also explained. Historical accounts trace the development of the Smithsonian’s mineral and gem collections, emphasizing the complementary roles of exhibition specimens, reference material, and scientifically documented samples. Famous jewels, including the Hope diamond and earrings associated with Marie Antoinette, illustrate the collections’ historical significance. Color photographs, many specially taken by Chip Clark, combine specimen portraits with explanatory captions, making the volume both an accessible scientific introduction and a visual companion to the museum’s displays.

corundum, ruby, Vietnam.12, inclusions.5, gems

Rubies from newly developed deposits near Luc Yen in northern Vietnam are described through their geological occurrence, physical properties, absorption spectra and microscopic features, with particular emphasis on their resemblance to rubies from Mogok, Myanmar. First reported in 1988 and received by the author for examination in September 1989, the Vietnamese material ranges from pale to dark red, sometimes with a weak to moderate violet tint. The deposits lie approximately 270 km northwest of Hanoi. Marble is identified as the source rock, although the stones are recovered from secondary deposits, particularly brownish lateritic sediments, as rounded, water-worn pebbles. A direct geological connection between the Vietnamese and Myanmar marble-hosted ruby occurrences had not been established. Measured physical properties fall within the normal range for corundum, including birefringence of 0.008 and specific gravity of 3.93–3.98. Absorption spectra exhibit the characteristic chromium bands in the green and violet regions and a red chromium line at 692 nm. Fluorescence is strong red under long-wave ultraviolet radiation and red under short-wave ultraviolet radiation. Microscopic examination reveals the inclusions and structural features characteristic of marble-hosted ruby. Common observations include twinning lamellae, fine rutile, healed fractures, crystal inclusions, and growth and colour zoning. Twin lamellae parallel rhombohedral faces and intersect at approximately right angles; tubes containing a polycrystalline substance, probably boehmite, may occur within them or along their intersections. Fine rutile needles form dust-like clouds that commonly follow growth planes. Healed fractures contain either small rounded liquid-filled cavities or more elongated cavities. Heat treatment can modify the latter into worm-like shapes, which may be partly filled with an artificial glass-like substance. Discrete crystal inclusions are comparatively uncommon, but rounded transparent carbonates and zircons, sometimes accompanied by tension cracks, were observed. Distinct growth structures frequently coincide with colour zoning, and colour can be distributed unevenly. The study concludes that these Vietnamese rubies display the typical internal characteristics of marble-hosted ruby and closely resemble material from the commercially important Mogok deposits.

gems, lapis lazuli, Afghanistan, gem trade, Central Asia, Pakistan, Mehrgarh

Lapis lazuli working at Mehrgarh, Pakistan, dates back to the 4th millennium BC, as documented by Massimo Vidale and Maurizio Tosi in their 1990 study published in Paléorient (Vol. 16, No. 2, pp. 89–99). Their research highlights evidence of early lapis working techniques in one of the earliest Neolithic settlements of South Asia. The Chagai Hills are considered a possible source of the material, with lapis lazuli from this region characterized by a greenish hue due to diopside inclusions—an observation consistent with later gemological accounts, including those in ExtraLapis. Earlier use of lapis at Mehrgarh has also been noted by Jarrige (1985: 285), who reports finds from Period I, dating to the 7th millennium BC, making it one of the earliest known occurrences of lapis lazuli use, as later referenced by Moorey.

gems, beryl, emerald, Egypt, inclusions

The aim of latest expedition to Djebel Sikeit and Djebel Zabarah by the brothers Angelo and Alfredo Castiglioni was the re-discovery of the Pharaoh's emerald mines. The Castiglioni expedition was successful in the re-discovery of these forgotten ancient mines and has collected samples and documents on these famous deposits of precious stones, providing emer- ald specimens of great interest to gemmologists and archaeologists, as will be revealed in this paper.

corundum, sapphire, Malawi.12, inclusions.5, gems

Describes newly available gem-quality blue sapphires from Malawi. The material has refractive indices of 1.762–1.770, birefringence of 0.008, and specific gravity of 3.97–3.99. Chemical analyses detected FeO, TiO and Cr₂O₃, while absorption spectroscopy indicates that the blue coloration results principally from Fe²⁺–Ti⁴⁺ intervalence charge transfer, together with Fe³⁺ absorption. Microscopic examination revealed lamellar twinning and inclusions of boehmite, rutile and zircon. The report supplements earlier studies of red and orange corundum from Malawi and documents the occurrence there of transparent blue gem-quality sapphire.

corundum, inclusions.5, Burma.12, gems