gems, peridot, olivine, Pakistan

Following the Fall 1994 Gem News report on a new peridot source in Pakistan’s far western Himalayas, further study of both rough and cut stones from the deposit has been conducted. The orthorhombic peridot crystals may initially appear hexagonal due to the symmetry of “columnar” and “pyramidal” faces, with face types identified using Goldschmidt’s Atlas der Krystallformen. Prominent faces included basal pinacoid (001), columnar (010) and (110), and pyramidal (021) and (111), with striations visible along the c-axis on the (010) and (110) faces, though many crystals, as confirmed by Laura Thompson of Shades of the Earth, also exhibit well-formed, lustrous faces. Two faceted stones—a 5.23 ct rectangular mixed cut and an 18.37 ct cushion modified brilliant—showed gemological properties consistent with known peridot: medium yellowish green color, transparent diaphaneity, R.I. values of α = 1.651, β = 1.669, γ = 1.687 (birefringence 0.036), specific gravity of 3.35, weak pleochroism, inert fluorescence, and distinct absorption bands at ~453, 477, 497 nm, and a weaker one at ~529 nm. These values suggest a composition of ~90% forsterite and 10% fayalite. No inclusions were visible under magnification in the faceted stones, though black rod-like inclusions, identified as ludwigite via X-ray diffraction, were noted in some cabochon-grade rough.

gems, garnet, grossular, hessonite, India, Orissa, Ghatpara, Dahikbala, Budhido, and Burubura

Hessonite garnets from the villages of Ghatpara, Dahikbala, Budhido, and Burubura in Orissa, India, are located in the high-grade metamorphic khondalite suite and occur either in calc-silicate lenses or in quartzite-amphibolite contact zones. The paragenesis of Orissa’s hessonite is linked to regional metamorphic processes, probably during Middle Proterozoic times. The colours of the stones range from pale yellowish and orange to brown, with refractive indices and densities for each locality as follows: Ghatpara: n = 1.738–1.752, D = 3.56–3.64 g/cm³; Dahikbala: n = 1.750–1.756, D = 3.58–3.64 g/cm³; Budhido: n = 1.751–1.758, D = 3.60–3.63 g/cm³; Burubura: n = 1.759–1.763, D = 3.60–3.66 g/cm³. In addition to calcium, aluminium, and silicon, chemical analyses reveal a distinct content of iron and traces of manganese and titanium. Microscopical study shows that the hessonite from Ghatpara is characterized by mineral inclusions, healing cracks with two- or three-phase inclusions, and growth marks which sometimes display strong interference colours under crossed polarizers. The inclusions in stones from Burubura are mainly healing cracks with two- or three-phase inclusions and growth marks. Budhido hessonite exhibits a strong oily appearance and mineral inclusions, while Dahikbala stones are marked by needle-like inclusions, growth marks, and some mineral inclusions.

gems, glyptic, engraved gems, agate, cameo, intaglio, mtorolite, chrome chalcedony, archaeology, archaeogemology

A green intaglio, described by the seal specialist as ‘plasma’, was identified as a chalcedony colored green by chromium. This is of particular interest as chrome green chalcedony is supposed to have been first discovered in Africa in 1955.

gems, ancient gems, glyptic, archaeology, archaeogemology, beads

Lepcis Magna (Libya), one of the greatest cities of North Africa and one of the most famous archaeological sites in the Mediterranean, was situated in the region (later province) of Tripolitania. Birthplace of the emperor Septimius Severus, the city has yielded many well- preserved monuments from its Roman past, but the extraordinary architecture and history of this city has never been examined in the context of the ancient region as a whole, encompassing north-west Libya and southern Tunisia. David Mattingly has filled this gap, presenting important new research on the military frontier, the pre-Roman tribal background, the urban centers, and the regional economy. Drawing on recent excavations and field surveys, he reinterprets many aspects of the settlement history of this marginal arid zone that once was prosperous. Partly through large-scale cultivation of olives, one of the least promising environments of the Mediterranean hosted one of the wealthiest Roman provincial towns–Lepcis Magna. David Mattingly also considers many wider themes in Roman provincial studies: Romanization, the military strategy on the frontiers, and the economic links between provinces and the sources of elite wealth. The dramatic rise and premature decline of this region, over the 500-year period between Caesar's victory at Thapsus in 46 B.C.E. and the conquest of North Africa by the Vandals, make it one of the most unusual provincial histories of the Roman world. David J. Mattingly is Lecturer in Roman Archaeology, University of Leicester.

gems, spinel, Sri Lanka

An unusually coloured natural spinel examined after the 1994 Tucson gem show provides evidence that nickel can contribute to the colour of natural spinel. The 4.88-carat cushion-cut stone, reportedly from Myanmar, displayed a slightly greenish blue or “teal” colour rather than the saturated royal blue more commonly associated with natural cobalt-bearing spinel. Standard gemmological testing gave a refractive index of 1.714, anomalous double refraction, and a specific gravity of 3.60. The specimen was inert to long-wave and short-wave ultraviolet radiation, fluoresced red under visible light, and showed a moderate red reaction through a colour filter. A handheld spectroscope revealed broad absorption bands near 460, 550, and 585 nm, together with total absorption above 610 nm, consistent with natural cobalt-blue spinel. Microscopic examination found the stone essentially clean apart from elongated yellow stains in surface-reaching fractures near a corner of the table; these could be mistaken for flux inclusions. Energy-dispersive X-ray fluorescence analysis supported natural origin through substantial zinc and gallium contents typical of natural spinel. In addition to magnesium and aluminium, the analysis detected abundant iron, trace manganese, and an unusually high nickel content compared with other natural blue spinels in the laboratory’s database. Cobalt was not detected, as its usual concentration in natural cobalt-blue spinel lies below the instrument’s detection limit. Ultraviolet–visible absorption spectroscopy identified a transmission window near 500 nm, compared with approximately 490 nm in typical royal-blue cobalt-bearing spinel. This shift towards greenish blue was attributed to a broad absorption underlying the principal cobalt feature. Absorption at 480 nm was also approximately as intense as that at 460 nm, whereas the former is usually weaker in other natural cobalt-blue spinels. Comparison with a Russian flux-grown synthetic spinel doped with divalent nickel suggested that nickel caused the additional absorption, consistent with the chemical analysis. The authors regarded the specimen as the first reported example of nickel contributing to the colour of natural spinel.

jade, jadeite, fei cui, assembled stones, treatments, Burma, gems

Two examples of coated fei cui illustrate a treatment in which surface varnish improves colour and appearance while producing gemmological properties that can obscure the identity and treatment of the underlying material. During a visit to Taiwan, an editor examined a 117.99 ct bead, approximately 24 mm in diameter, supplied by Ten S.-T. Wu and Peter Chiu. The bead consisted of greyish purple fei cui covered with mottled green varnish and, viewed from a distance, convincingly resembled fine-quality material. Closer examination revealed that part of the coating had spalled away, exposing the original colour. Its refractive index of 1.52 was too low for fei cui and was attributed to the coating, while its specific gravity of 3.29 was slightly below the usual value. Strong chalky blue fluorescence under long-wave ultraviolet radiation, with a weaker short-wave reaction, was also considered to originate primarily from the varnish; natural fei cui fluorescence was described as generally spotty and yellowish white. Contact with a hot point melted the coating. A similarly treated pipe, approximately 8 cm long, was coated externally but not internally. Refractive-index readings of 1.54 on coated areas and 1.66 on exposed material distinguished the surface layer from the substrate. A moderate absorption line at 437 nm supported identification of the underlying material, which was further confirmed by energy-dispersive X-ray fluorescence comparison with documented reference samples. Reflected-light microscopy of chipped areas revealed two distinct coatings: an inner mottled green layer apparently intended to enhance colour and an outer colourless or very pale yellow layer interpreted as a protective varnish. Both fluoresced yellow-green under ultraviolet radiation, with differing intensities, whereas the substrate was inert. Infrared spectroscopy showed strong absorption around 2900 cm⁻¹, consistent with an organic coating. Because comparable absorption can occur in bleached and polymer-impregnated B-type fei cui, the authors emphasise that infrared evidence alone could lead to an erroneous diagnosis of impregnation. Microscopic examination of the surface, supported by optical, spectroscopic and chemical observations, established coating as the treatment present.

corundum, jade, jadeite, fei cui, gems

corundum, synthetic corundum.7, gems

Flux treatment of synthetic ruby is reviewed, and a previously uncharacterised inclusion pattern is described in stones encountered in the gem trade, often represented as natural rubies from Afghanistan. Conventional treatment involves immersing Verneuil flame-fusion synthetic ruby in an aluminium oxide-bearing flux, which penetrates fractures and promotes partial healing, leaving residual flux arranged in fingerprint-like patterns that can resemble healed fractures in natural ruby. Such treatment can also obscure curved growth striations. Products associated with Chatham, Knischka, and Lechleitner are discussed, although the authors note that preliminary heating and quench cracking have not been experimentally demonstrated for every product. Treatment may produce a flux-grown synthetic ruby overgrowth on the Verneuil core; remnants can reveal distinct boundaries, parallel growth lines, coarse flux inclusions, or small synthetic corundum crystals. Identification may depend on curved growth striations, gas bubbles following curved growth layers, or trace-element detection of molybdenum, lead, or tungsten derived from the flux. Since 1989, the authors had encountered approximately 60 treated synthetic rubies with a different inclusion structure. Twenty were examined by standard gemmological methods, and two, weighing 1.99 and 9.93 carats, underwent scanning electron microscopy with energy-dispersive spectroscopy and energy-dispersive X-ray fluorescence analysis. These stones contained thin, continuous, three-dimensional networks of flux-filled fractures, producing a honeycomb-like cellular appearance in transmitted light and whitish to colourless surface-reaching networks in reflected light. Their refractive indices, specific gravities, ultraviolet fluorescence, and absorption spectra fell within ranges that overlap those of natural and synthetic ruby. Extremely weak curved striations were resolved in one sample, but were insufficient to establish Verneuil growth conclusively; Czochralski growth remained possible. Analysis of the fracture fillings detected calcium and lead but no aluminium. The authors infer treatment in a flux possibly containing lead fluoride and calcium fluoride, while emphasising that the precise procedure remains unknown. The absence of dissolved aluminium oxide, insufficient treatment duration, or a different treatment process could account for the lack of conventional partial-healing patterns. Unlike the discontinuous fingerprints typical of earlier treated synthetics, the continuous cellular networks generally do not resemble natural ruby inclusions and permit ready identification with a gemmological microscope or even a hand lens.

corundum, geology.11, gems

corundum, UK.12, Scotland.12, gems