corundum, Australia.12, gems

gems, diamond, imitation diamond, gemology

Gübelin surveys diamond and the principal materials used to imitate it, emphasizing the gemological properties by which natural diamond can be distinguished from simulants. He discusses diagnostic characteristics such as refractive index, dispersion, hardness, specific gravity, luster, thermal behavior, and optical appearance, showing how combinations of relatively simple gemological tests permit reliable separation. The article reflects the increasing variety and quality of diamond imitations available around 1980 and stresses systematic identification rather than reliance on visual appearance alone.

synthetic gems, synthetic corundum.7, synthetic beryl, emerald, gems, beryl

The production of synthetic and imitation gemstones is reviewed through the relationships between crystal growth methods, material properties, gemmological identification and commercial feasibility. Synthetic gems are distinguished from imitations by their correspondence to natural materials in composition and structure, whereas imitations reproduce appearance using different substances. The principal methods considered are Verneuil flame fusion, Czochralski pulling, Bridgman solidification, skull melting, flux growth, hydrothermal growth and high-pressure synthesis. Their suitability depends on melting behaviour, viscosity, phase stability, growth rate, crystal perfection, equipment investment, operating skill and production costs. Diamond growth is described in terms of high-pressure solution transport through a molten metal solvent onto cooler seeds, with controlled impurities producing yellow or blue material. At the time of writing, gem-quality synthetic diamond remained costly relative to natural diamond, although technical improvements offered possible future competition. Emerald requires solution growth, and the authors reconstruct aspects of incompletely disclosed commercial flux and hydrothermal processes from published evidence, patents and inclusions. Water content, optical constants and characteristic inclusions are discussed as indicators of growth history. Corundum receives detailed treatment, particularly the inexpensive Verneuil process, its feed preparation and thermal conditions, and the origin of diagnostic curved growth striations. Synthetic star ruby and sapphire are produced by incorporating titanium and subsequently precipitating oriented rutile needles through heat treatment. Alternative corundum methods provide improved crystal quality or different growth forms, often for technological applications. Hydrothermal quartz production illustrates the transfer of industrial crystal growth technology into jewellery, with impurities, irradiation and heating controlling colour. Further sections cover spinel, chrysoberyl and alexandrite, cubic zirconia, yttrium aluminium garnet, gadolinium gallium garnet, rutile and strontium titanate. Skull melting is highlighted as the means of overcoming containment difficulties in growing cubic zirconia. Synthetic opal is explained through the preparation, regular packing and consolidation of uniform silica spheres, while turquoise and other aggregate materials raise questions about the criteria for a true synthetic equivalent. Appendices introduce gem properties, valuation, shaping and testing. The authors emphasise that successful synthesis alone does not ensure a viable gem product: durability, appearance, consumer demand and distribution also matter. Future developments are expected particularly from research supported by technological applications, improved production economics and materials displaying special optical effects.

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

Mineralogy of semi-precious gems, such as nephrite, tremolite cat's-eye, blue chalcedony and veined stones, from Taiwan are reviewed, supplemented with some data (Fig.1). Nephrite and cat's-eye tremolite occur at the contacts of graphite-sericite schist and serpentinite sills in association with asbestus, talc and diopside-dominant skarn near Hualien (Fig.2). Cat's-eye tremolite was formed evidently later than nephrite. Nephrite jade is spinach-green to yellowish green in color; translucent to opaque. H. : 6.5; G. : 3.007-3.014. It is composed of sub-parallel tufts of fibrous tremolite in interfelted base with nephritic texture, accompanied by minor chromite, magnetite, picotite, garnet and chlorite which give rise to black spots or streaks (Fig.3). α : 1.609-1.612, β : 1.620-1.621, γ : 1.631-1.633; γ-α : 0.021-0.022. Noteworthy is that the Taiwan jade is similar in mineralogy to the New Zealand jade. Tremolite cat's-eye varies in color, from greenish yellow to black; translucent to opaque. H : 6-7, G. : 3.000-3.045. It consists solely of fine, Ionger sub-parallel fibers of tremolite without nephritic texture. α : 1.612-1.613. β : 1.620-1.626, γ : 1.637=1.639; γ-α : 0.024-0.027. Both nephrite and cat's-eye are similar in X-ray data to tremolite from St. Gotthard, Switzerland (Table 1). Chemical analyses also revealed that no marked differences in cornposition exislt between nephrite jade and cat's-eye and between cat's-eyes of various colors, all showing about 10 % of the ferro-actinolite molecule (Tables 2 & 3). Minor uvarovite with 10% Cr_2O_3 and vesuvianite were first found in Taiwan (Tables 5 & 6). Blue chalcedony occurs as irregular small veins in andesitic agglomerate north of Taitung. It is deep sky-blue to greenish blue in color; opaque to translucent. H. : 7; G. : 2.581; n : 1.539. Traversed by veinlets of chalcedony-quartz and quartz-pyrite, it consists mainly of radial-fibrous aggregates of chalcedony, with minor chlorite, opal and iron hydroxides (Fig. 5). Veined stones are produced on the Penghu Islands as globular concentric aggregates chiefly of calcite, aragonite and siderite in the amygdaloidal cavities of olivine-augite basalt (Figs.5 & 6). H : 3-4; G. : 2.83-3.30. Some gemological features of these gem materials are also given (Fig.4).

synthetic corundum.7, flux, inclusions.5, gems

Five oval faceted synthetic blue flux sapphires, each weighing approximately 2 ct, grown by Chatham Industries were examined. The company had been experimenting with the growth of flux-melt blue sapphires for several years, but its early products were heavily included and unsuitable for faceting. The five recently examined stones were dark blue, with strong color zoning in two specimens. The zoning ranged from near colorless to deep blue and was confined to definite straight-sided, angular patches reflecting the growth and structure of the original crystal. Platinum flakes and splinters resembling submetallic included crystals were also observed. The most common inclusions were residual flux, which occurred as white, thick, veined, fingerprint-patterned curving layers, whitish curving and flowing smoke-like clouds, or a combination of both forms. The hydrostatic specific gravity ranged from 3.98 to 4.06, with platinum inclusions likely contributing to the higher values. Refractive indices were relatively consistent, ranging from 1.763 to 1.772, with a corresponding birefringence of 0.009. Spectroscopic examination revealed a very vague absorption band centered at 451.5 nm in the blue region, which was not diagnostic. X-ray fluorescence ranged from pale white through faint bluish white to yellowish white, with no phosphorescence observed after X-ray excitation. Under short-wave ultraviolet radiation, the sapphires showed dull brownish white fluorescence, while long-wave ultraviolet radiation produced a moderate whitish yellow glow. During exposure to both long- and short-wave ultraviolet radiation, two stones displayed distinct patches of bright yellow fluorescence. No inclusion centers for this fluorescence were observed under the microscope, and the bright yellow areas were not bordered by optically detectable irregularities.

gems, archaeology, archaeogemology, India, Indus River Civilization, Harappa, Pakistan, Iran

Since the early 1930s, archaeologists have identified a corpus of soft-stone vessels carved in a highly diagnostic style, found at sites ranging from Mesopotamia to the Indus Valley. Approximately 300 vessels or fragments have been recovered from at least 28 locations across Southwest Asia (figures 1 and 2), all sharing a common and easily recognizable repertoire of design elements, limited shape types, and a consistent use of related soft green stones, particularly chlorite and talc. In a broader study (Kohl 1975), these objects were termed Intercultural Style (IS) vessels. Although the origins of the style remain debated, stratigraphic evidence from Mesopotamia and the concentrated presence at Tepe Yahya suggest a relatively brief period of production and circulation, best dated to the mid-third millennium B.C. More recent excavations at Shahdad and Tepe Yahya in southeastern Iran, along with illicit digs on Tarut Island in the Persian/Arabian Gulf, have significantly reshaped our understanding of their distribution. While earlier scholars such as Frankfort (1954), Woolley (1935), and Piggott (1950) proposed origins in Mesopotamia, southwestern Iran, or Baluchistan, current evidence shows that the majority of finds come from Kerman province in southeastern Iran (plate 3), as well as from Tarut and Failaka Islands in the Gulf.

synthetic beryl, emerald, gems

As-grown and faceted crystals of synthetic hydrothermal emeralds from the USA and USSR were compared in terms of morphology, internal features, and physical properties. The USSR emeralds are notably closer to natural emeralds in physical and optical properties, although both types differ from natural stones primarily in their internal features. USA emeralds (SG: 2.67–2.68, RI: ω 1.572–1.574, ε 1.568–1.569) display bright red fluorescence under 365 nm UV, show Chelsea filter reactions (red), and often contain optical strain, “earthworm” cracks, phenacite, and 2- or 3-phase inclusions—often originating from natural beryl seed plates. USSR emeralds (SG: 2.70–2.71, RI: ω 1.583–1.586, ε 1.577–1.579) are slightly softer (H 7–7.5), show weaker UV fluorescence and pleochroism closer to natural emeralds, and lack spikes or strong zonation. Their inclusions include more naturalistic features like “wheat-head” textures, 2- and 3-phase inclusions, and reddish-brown plates. Growth habits differ slightly, with the USSR stones typically showing multiple growth planes ({112̅1} and {112̅0}) and shorter estimated growth times. Overall, USSR hydrothermal emeralds reach ~90% similarity to natural emeralds, versus ~80% for USA stones and 40–60% for flux-grown emeralds.

inclusions, gems

Gübelin investigates mineral and fluid inclusions in phenakite from Brazil to reconstruct stages of crystal growth and assess the nature of the mineral-forming solution. Three phenakite crystals containing unusual acicular aikinite inclusions were supplied by Pete Dunn following an earlier report of the occurrence. The largest specimen contained two adjacent, parallel aikinite crystals, one projecting into a slender cavity and occupying approximately 98% of its volume. The remaining space held liquid, a gas bubble, and an unidentified anisotropic solid. Further examination revealed small green needles and numerous fluid inclusions along a partially healed fracture. Electron-microprobe analysis of the green needles detected lead, copper, bismuth, and sulphur, supporting their identification as altered aikinite. Their green, disintegrated condition is interpreted as evidence that they existed and underwent alteration before incorporation into the growing phenakite, making them protogenetic inclusions. Fresh aikinite needles and the associated primary fluid cavity represent inclusions formed during host growth, whereas the fracture-related fluid inclusions are classified as pseudosecondary because they were trapped before growth ended. Microthermometric examination involved cooling to −140 °C and subsequent controlled warming. In the primary inclusion, ice began melting at −2.5 °C, carbon dioxide hydrate dissociated near +8 °C, and minute solid grains disappeared between +20 and +50 °C. The anisotropic solid remained undissolved at +60 °C. Gübelin interprets the fluid as a dilute aqueous saline solution containing 4.2 wt% sodium-chloride equivalent and a detectable carbon dioxide component below 6 wt%. The pseudosecondary inclusions, measuring approximately 5–350 µm, contained liquid, gas, and several solid phases. Ice melting began at −2.1 °C and hydrate dissociation occurred near +9 °C, yielding an estimated salinity of 3.5 wt% sodium-chloride equivalent and a similarly low carbon dioxide content. Their comparable fluid compositions suggest limited chemical change between the two trapping episodes, possibly separated by only a short interval. The daughter solids indicate a more complex original solution, although their identities remained unresolved. Together, the three inclusion generations document successive events before and during phenakite growth and support a hydrothermal origin for the host crystal.

corundum, Australia.12, gems

corundum, quality.10, Kremlin, Tajikistan.12, spinel, gems

David Douglas Duncan’s Great Treasures of the Kremlin is a lavishly illustrated photographic and historical survey of the Russian imperial treasures preserved within the Moscow Kremlin, particularly the collections of the Armory Chamber, its cathedrals, and royal palaces. Beginning in 1956, Duncan made five visits to Moscow over three years, obtaining exceptional permission from Soviet authorities to photograph the Kremlin’s interiors and treasures in color. His photographs, taken with 35 mm Leica cameras, are accompanied by historical narratives and a substantial research supplement providing additional information on individual objects, their materials, craftsmanship, provenance, and historical associations. The book traces the development of the Kremlin from a medieval fortress into the ceremonial and political center of Russia, emphasizing the accumulation of precious objects under successive grand princes, tsars, and emperors. Of particular gemological interest are the elaborate crowns, ecclesiastical ornaments, jeweled Gospel covers, ceremonial weapons, and imperial regalia incorporating diamonds, rubies, sapphires, emeralds, turquoise, topaz, garnets, and pearls. The Cap of Monomakh, the traditional symbol of Russian sovereignty, is described as a gold filigree headdress decorated with emeralds, rubies, and pearls, its origins obscured by legends associating it with Byzantium. The Cap of Kazan, commissioned by Ivan the Terrible following his conquest of Kazan in 1552, features intricate gold filigree, turquoise, pearls, rubies, and a large yellow topaz that replaced an earlier ruby. Other notable objects include the diamond-encrusted crown of Peter the Great, the crown of Empress Anna incorporating diamonds from Catherine I’s crown, and the magnificent jeweled orb and throne of Tsar Alexei Mikhailovich. Duncan also documents the exceptionally rich ecclesiastical treasures of the Russian Orthodox Church, including a seventeenth-century patriarchal mitre decorated with emeralds, rubies, enamel, and pearls, and a Gospel cover commissioned during the reign of Feodor Alexeievich containing fifty-seven pounds of gold and numerous pear-shaped emeralds. The jeweled Gospel book presented by Ivan the Terrible in 1571 is particularly remarkable for its rubies, large sapphires, golden topazes, silver reliefs, and enamel decoration. Earlier Russian goldsmithing traditions are represented by the thirteenth-century Ryazan treasure, comprising gold filigree ornaments decorated with garnets and enamel. The book further illustrates pearl-embroidered ecclesiastical vestments, elaborate icon covers, gold and silver ceremonial vessels, jeweled horse trappings, and precious objects exchanged as diplomatic gifts. Among the latter is an Ottoman presentation to Catherine the Great incorporating rubies, diamonds, gold, and a large emerald. Duncan concludes with the Romanov dynasty’s decline, including the magnificent Fabergé egg commemorating its tercentenary in 1913, and the preservation of imperial treasures following the Russian Revolution. Although primarily a photographic history rather than a systematic gemological catalogue, the volume provides valuable visual documentation of historic gemstone settings, goldsmithing, enameling, pearl embroidery, and the ceremonial use of precious materials in Russian court and religious art.