synthetic corundum.7, synthetic ruby, hydrothermal, gems

A hydrothermal ruby acquired by the Gemmological Association is described, with emphasis on the microscopic features distinguishing its natural seed from the synthetic ruby grown around it. The specimen had a relatively thick hydrothermal overgrowth deposited on a natural ruby core. Examination by E. Gübelin confirmed observations he had published in 1961 on hydrothermal ruby produced in the United States. Under dark-field illumination, the seed was readily visible and clearly distinguishable from the surrounding synthetic material. Its natural inclusions consisted of microlites surrounded by liquid films, whose appearance led Gübelin to suggest that the seed was probably a ruby from Siam, now Thailand. The geographical attribution was tentative and based on the appearance of the natural inclusions. The hydrothermal overgrowth contained characteristic gaseous markings, illustrated as irregular tubes and hose-like forms. Photomicrographs taken in transmitted light showed these inclusions and their relationship to the natural core. Dark, paired growth lines meeting at angles characterised the natural seed, while numerous gaseous inclusions occurred along the boundary between the seed and its synthetic overgrowth. A further illustration showed the overall distinction between the two components and the natural inclusions retained within the core. The specimen’s physical properties corresponded to those reported by Gübelin in 1961, although numerical measurements were not supplied in this account. Its colour was dark red, an appearance the report considered sufficient to arouse suspicion. Nevertheless, a gemmologist who examined it briefly under a microscope incorrectly concluded that it was natural. This incident demonstrates the identification problem presented by a synthetic overgrowth surrounding a naturally included seed: observing natural inclusions in one part of a stone does not establish that the entire specimen is natural. The report therefore stresses careful microscopic examination before determining a ruby’s nature, particularly recognition of the boundary between the core and overgrowth and the contrasting inclusion populations on either side. Dark-field illumination was especially effective in revealing this distinction.

gems, jade, jadeite, fei cui

Chemical, optical and X-ray investigations demonstrate that jadeitic pyroxenes in California’s Franciscan metagraywackes contain substantial proportions of other pyroxene components and should not be treated as pure jadeite when interpreting metamorphic conditions. A purified concentrate from Angel Island, San Francisco Bay, was analysed chemically and examined for its physical properties, with comparisons drawn from Valley Ford, Pacheco Pass and previously described material from Celebes. The compared metagraywacke pyroxenes contain approximately 80–87 mol% jadeite, together with diopside, acmite and hedenbergite components. The Angel Island pyroxene has refractive indices of approximately 1.670, 1.671 and 1.678, birefringence of 0.008, strong optical dispersion and a measured density of 3.32 g/cm³, closely matching its calculated density of 3.33 g/cm³. Its unit-cell volume is slightly greater than that of nearly pure jadeite, reflecting compositional substitution. These characteristics distinguish the metagraywacke pyroxenes both from nearly pure jadeite in silica-deficient rocks enclosed by serpentine and from the less jadeitic omphacites of eclogites. The host rocks typically retain sedimentary textures and lack conspicuous schistosity, making field recognition difficult, although increased density provides a useful preliminary indication. Their characteristic assemblage comprises quartz, jadeitic pyroxene, lawsonite and muscovite, with variable glaucophane, aragonite, calcite and chlorite. Jadeitic pyroxene forms fine prismatic aggregates containing graphite and quartz inclusions. Albite is generally absent from the pyroxene-bearing groundmass but occurs in quartz veins lacking ferromagnesian minerals, suggesting that pyroxene formation involves reactions between albite and minerals such as chlorite rather than simple decomposition of albite alone. Comparisons of whole-rock analyses, sodium-to-potassium ratios and normative feldspar proportions reveal no significant chemical distinction between metamorphosed and unmetamorphosed graywackes and provide no requirement for introduction of alkalis during metamorphism. Reactions involving albite, chlorite or montmorillonite, and calcium carbonate are proposed to generate jadeitic pyroxene, glaucophane and quartz while releasing water and carbon dioxide. Incorporation of non-jadeite components may permit pyroxene formation at lower pressures than those experimentally established for pure jadeite plus quartz, but the magnitude of this effect remains uncertain and requires further investigation. Coexisting aragonite and lawsonite nevertheless support formation under high-pressure, relatively low-temperature conditions. An intermediate assemblage containing lawsonite, albite and chlorite is proposed to connect greenschist and glaucophane schist facies, with further regional mapping needed to establish their structural and metamorphic relationships.

corundum, sapphire, Brazil.12, geology.11, gems

About four years ago, Professor J. E. de Souza Campos of the University of São Paulo, Brazil, reported on a new sapphire from Brazil. He mentioned strange inclusions, unknown until now in sapphire and resembling rounded gas bubbles so typical of synthetic corundum. At the author’s request, Professor de Souza Campos very kindly made available two cut stones of this sapphire and later some raw material, which could be tested more easily. The locality of these sapphires is quoted by de Souza Campos as Jauré and Quilombo, Rio Coxim, Mato Grosso. He found the refraction for sodium light to be nₒ = 1.770, nₑ = 1.762, and the birefringence 0.008. The dichroism for blue-coloured stones is o = blue to violet blue, e = green; for greenish-coloured stones o = green, e = yellow-green. With the hydrostatic balance he determined the specific gravity at 3.952 to 4.052. The stones exhibit a dark blue colour but, regrettably, the transparency is considerably reduced by many inclusions. At a first sight through the microscope, many of them indeed resembled rounded gas bubbles. But when using a higher magnification, it is seen that two kinds of inclusions are present: liquid and gas-filled discs, and negative crystals, many of them exhibiting rounded forms.

corundum, Australia.12, inclusions.5, gems

Examination of a parcel of approximately thirty blue Australian sapphires reveals exceptionally closely spaced growth zoning that can resemble the fine striations associated with synthetic corundum. The stones, submitted by John Fleming of New Zealand, attracted attention because their growth bands were of a similar order of size to those seen in synthetic material. Although the observed striations showed no curvature, this distinction alone was insufficient to resolve their origin immediately: in small stones fashioned from a large synthetic boule, curvature may be inconspicuous, particularly under strong magnification. The report therefore identifies a potential difficulty in interpreting fine zoning when only a limited portion of a growth structure is visible within a faceted stone. Further microscopic examination disclosed convincingly hexagonal zoning in some specimens, together with healed fractures, providing additional evidence for their identification as natural sapphires. Photomicrographs illustrate both the closely spaced straight bands that initially prompted concern and the more diagnostic hexagonal pattern found during the subsequent investigation. Other observations document the physical and optical characteristics of the parcel. Testing in Clerici solution showed the stones to have densities slightly greater than that of a reference sapphire with a density of 3.995, although individual numerical determinations were not reported. Refractive indices measured with a Rayner refractometer in sodium light ranged from 1.765 to 1.780. Dichroism was pronounced, producing green and purple shades of the blue body colour. Examination between crossed nicols revealed neither strain nor twinning, and no further features of particular interest were recorded. The stones were described as richly blue but somewhat dark. The principal contribution is the documentation of unusually fine natural growth zoning whose scale and appearance approach those of synthetic corundum. Its diagnostic implication is that closely spaced striations should be assessed through their geometry and associated internal features, with particular attention to the possibility that a small field of observation can conceal curvature. The note offers an observational account of this identification problem rather than an explanation of the geological conditions responsible for the exceptionally narrow zones.

corundum, gems

Farn outlines a systematic approach to ruby identification, emphasizing the distinction between establishing a stone as corundum and determining whether it is natural or synthetic. Although experienced observers may recognize characteristic appearances and inclusions immediately, he argues that laboratory conclusions require corroborating tests rather than intuition or commercial reputation. Refractive-index measurements and the characteristic chromium spectrum establish ruby but do not distinguish natural from synthetic material. The spectrum is described through its red doublet, broad absorption across the yellow-green region, and fine absorption lines in the blue; Farn favours spectroscopy for small or worn stones because it avoids contact with the comparatively soft refractometer prism. Microscopic examination provides the principal evidence of origin. Features discussed include rutile silk, mineral crystals, twin planes, feathers, and the uneven colour distribution termed “treacle,” which Farn associates particularly with Burmese rubies. He contrasts these with features observed in Siamese material, including distinctive halo-like feathers surrounding opaque inclusions, while acknowledging that commercial geographical labels may follow colour and appearance rather than actual provenance. Particular attention is given to misleading similarities: natural crystals may resemble gas bubbles, synthetic bubble groups may suggest natural feathers, and internal colour effects may resemble striae in glass. Comparison specimens and repeated observation are therefore recommended. For apparently inclusion-free stones, immersion in a liquid approaching ruby’s refractive index reduces surface interference and assists the search for bubbles or curved growth structure. Farn describes rotating the specimen while adjusting focus, condenser height, diaphragm aperture, and illumination angle to reveal faint internal features. Excessive magnification may obscure slight curvature by restricting the visible length of a growth line, while focusing beneath the specimen can mistakenly bring bubbles or striae in the glass immersion cell into view. When microscopy remains inconclusive, he discusses X-ray transparency, X-ray-excited fluorescence and phosphorescence, and immersion contact photography. He regards phosphorescence following X-ray excitation as strong evidence of synthetic origin, illustrating the need for continued observation with a specimen whose afterglow appeared only after a delay. Short-wave ultraviolet fluorescence is treated more cautiously: differences in brightness may assist comparison within a parcel, but variation among natural rubies prevents its use as an independent diagnostic test. Immersion contact photography can disclose curved structure that escapes direct microscopic observation, and simple low-power examination against a diffusely illuminated white background may also prove effective. Throughout, Farn stresses the difficulty created by the closely similar optical and chemical properties of natural and synthetic ruby. His central conclusion is that careful interpretation of internal structure and inclusions, supported by complementary tests where necessary, provides the strongest basis for identification.

corundum, gems

Farn presents a practical account of sapphire identification, concentrating on the use of absorption spectroscopy when microscopic examination reveals no diagnostic inclusions. Drawing on routine testing experience, he describes an initial assessment of colour, cutting, and general appearance, followed by examination with a microscope or hand lens. Rotating the stone permits observation of silk, crystals, laths, twin planes, liquid feathers, two-phase inclusions, and colour zoning, which he regards as evidence of natural origin and, in favourable cases, geographical provenance. Dichroism and doubling of rear facets provide additional optical information, while refractive-index measurements establish corundum when an apparently inclusion-free specimen requires further investigation. Surface chatter or shatter marks are considered supplementary clues associated particularly with cheaply cut synthetic stones, although Farn explicitly acknowledges that they are not conclusive. The principal discussion concerns an absorption feature near 450 nanometres, which he presents as diagnostic of natural blue sapphire and absent from synthetic sapphire. His procedure begins by adjusting the spectroscope slit against daylight until the Fraunhofer lines appear sharp. A microscope with its eyepiece removed serves as an optical support, and a temporary ground-glass screen assists alignment of the lamp, specimen, and transmitted beam before the spectroscope is placed over the microscope tube. This arrangement permits examination of sapphires while still mounted in jewellery. Farn emphasizes adequate illumination and exclusion of stray light, recommending an aperture in cardboard beneath small specimens so that only light transmitted through the stone enters the instrument. He describes variation in absorption strength, contrasting the pronounced complex around 450–460 nanometres in iron-rich Australian sapphires with the weaker spectra commonly encountered in Ceylon material. Turning the specimen and slightly tilting the spectroscope may improve visibility of faint features. Practice with known natural stones is recommended to establish familiarity with the position and appearance of the spectrum before modifying the apparatus. The article also addresses heat generated by powerful lamps, noting that concentrated illumination can damage gemstones. A water-filled glass flask is proposed as both a condenser and a heat filter, while an additional flask containing copper sulphate solution suppresses the red portion of the spectrum and may enhance weak blue-region absorption. The account combines an experience-based testing sequence with detailed advice on alignment, illumination, filtering, and observation, illustrating Farn’s reliance on spectroscopy as a rapid aid to sapphire identification.

gems, Ceylon, Sri Lanka, ekanite, metamict mineral

Anderson, Claringbull, Davis and Hill describe ekanite, a newly recognized metamict mineral from the gem pits of Eheliyagoda in the Ratnapura district of Ceylon. Known since 1953 as green transparent-to-translucent pebbles, some fashioned as cabochons showing a gemstone-quality smoky asterism, the material was recognized as unusual by F.L.D. Ekanayake, after whom the mineral was named. Chemical analysis indicates a thorium-rich calcium silicate containing uranium, lead and minor rare-earth elements, with the approximate formula (Th,U)(Ca,Fe,Pb)₂Si₈O₂₀. The mineral is metamict, with refractive index about 1.5969 and density 3.276. Heating between 650 and 1,000 °C causes recrystallization to an X-ray powder pattern resembling thorite or zircon; at higher temperatures it melts and, if subsequently recrystallized, produces an X-ray pattern analogous to huttonite. Microscopic examination shows occasional larger opaque inclusions but no identifiable inclusions responsible for the asterism.

synthetic corundum.7, hydrothermal, gems

Gübelin investigates two recently introduced gem products—rubies represented as hydrothermally grown and natural beryl coated with synthetic emerald—emphasizing the identification difficulties created when synthetic growth surrounds a natural crystal containing convincing natural inclusions. He first reviews the hydrothermal synthesis of corundum developed by Laudise and Ballman at Bell Telephone Laboratories, describing the transport of dissolved nutrient through a temperature gradient in a pressurized vessel and its deposition on suspended seed crystals. Chromium supplies the ruby colour, while growth conditions and the materials used in the apparatus influence the resulting crystals. The ruby specimens personally examined, claimed to originate from Chatham, consisted predominantly of natural ruby cores covered by relatively thin synthetic layers. Their refractive indices, birefringence, specific gravity, dichroism, absorption spectra, and fluorescence provided no reliable separation from natural ruby. The cores contained rutile silk, mineral inclusions, and liquid feathers, while the overgrowth reproduced the original crystals’ external forms. Identification depended on minute features interpreted as gas bubbles within the surface layer, occurring singly or in lines, clouds, and planes, together with the abrupt termination of natural inclusions at the boundary between core and overgrowth. Gübelin notes that ordinary cutting could remove most or all of these thin coatings. The second product, manufactured by Johann Lechleitner and marketed as Emerita, comprised a previously fashioned natural beryl nucleus overgrown with a thin hydrothermal synthetic emerald mantle. The coating continued the crystallographic orientation of the seed, forming a continuous crystal rather than a cemented assembly. Its thickness varied with crystallographic direction and controlled the apparent colour. Standard gemmological properties again overlapped those of natural emerald, and refractometer readings primarily represented the synthetic surface. Microscopy, particularly with immersion and examination from the side, revealed the dark green rim around a pale or colourless core, occasional reflections at the interface, and characteristic structures within the overgrowth. These included parallel or intersecting tension fractures, partly healed fissures containing residual liquid droplets, and particles provisionally interpreted as other mineral phases, such as phenakite or euclase. Some particles obstructed growth and produced tapering cavities containing liquid and a bubble. High magnification and phase contrast helped clarify these delicate features and their relationship to the growth process. Gübelin concludes that natural inclusions within a seed cannot establish the natural origin of the entire stone. Careful examination must instead distinguish the core from its synthetic mantle. He also stresses that altered manufacturing conditions can eliminate many diagnostic inclusions; in exceptionally clean emerald coatings, the contrast between the green outer layer and pale interior may provide the only decisive evidence.

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, 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.