gems, inclusions, beryl, emerald, Brazil, Santa Terezinha de Goiás

Describes the emerald deposits of Santa Terezinha de Goiás, Brazil, presenting evidence for their stratiform occurrence and documenting the stones’ gemological properties, chemistry and inclusions. Refractive indices reach 1.593–1.602, with birefringence of 0.008–0.010, reported as the highest values then observed in emerald. Chromium and iron show the highest mean concentrations among Brazilian emeralds. Fluid inclusions are generally very small. Mineral inclusions include spinel, carbonates, mica, talc, amphibole and pyrite, with rutile, hematite, chalcopyrite, pentlandite and ilmenite also recorded.

gems, spinel, Tanzania, Morogoro, inclusions, spinel inclusions, högbomite inclusions

A 2.28 ct purplish pink faceted pear-shaped stone submitted to the West Coast laboratory was identified as natural spinel and reported by its owner to originate from Tanzania. Its refractive index was 1.714, and it was singly refractive with very weak anomalous double refraction. Hydrostatic specific gravity was approximately 3.60. The stone displayed strong red fluorescence under long-wave ultraviolet radiation, weak red fluorescence under short-wave radiation, and a characteristic absorption spectrum. Its most unusual optical feature was a moderate to strong whitish blue transmission effect observed when intense light was directed through a small opening onto the stone. The phenomenon was also visible without magnification when the spinel was held a few inches from an incandescent or fluorescent source, while a faint bluish haze could be seen at arm’s length in sunlight. The effect was interpreted as probably resulting from light scattering by minute inclusions or dislocations, comparable to similar reactions in other gem materials. Microscopic examination showed that the stone was only slightly included. Parallel rows of tiny octahedra, commonly encountered in spinels from classic Myanmar and Sri Lankan localities, were conspicuously absent. Instead, the dominant internal features were numerous sheets of polysynthetic twinning intersecting in two directions throughout the gem. Coarse needles or growth tubes were associated with these planes in several areas. Immersion in methylene iodide revealed faint color zoning apparently aligned with some of the twinning features. Densely packed clouds of minute particles occurred through much of the stone, appeared to represent exsolutions, and were oriented in three directions. A few small, thin, transparent, nearly colorless tabular euhedral crystals were also present. The combination of physical and optical properties, color, and visual appearance matched spinels attributed to a newly reported Tanzanian deposit that the author had examined during a visit to Idar-Oberstein. Tanzanian spinel was also available at the 1990 Tucson Show. The note documents distinctive optical and microscopic characteristics of this specimen while retaining its Tanzanian origin as a reported attribution.

corundum, asterism, 12–ray star, properties.3, gems

Unusual multiple chatoyancy in Australian sapphire is investigated through visual and microscopic examination of cabochons reportedly cut from Rubyvale, Queensland, and Inverell, New South Wales, rough. The study began with a Rubyvale sapphire measuring 10 × 8 × 4.5 mm that displayed a weak, diffuse white star together with three bright, mobile satellite reflections on its dome. Examination of two parcels revealed several comparable Rubyvale specimens, including four stones with three symmetrically arranged satellite reflections and three small twelve-rayed star sapphires; one specimen combined both features. The Inverell parcel yielded no comparable multiple chatoyancy, although one small stone displayed two stars attributed to twinning. Ordinary asterism is explained by reflection from crystallographically oriented acicular inclusions, whereas the additional reflections are associated with aligned, approximately equant platelets whose individual reflections appear as spots rather than lines. These inclusions occur predominantly in bands approximately parallel to prism faces, and rough angular measurements suggest reflecting surfaces inclined about 45° to the basal plane. Their mineral identity remains uncertain: non-acicular rutile, anatase and titanite are considered possible constituents. Most multiply chatoyant specimens were deep blue, strongly zoned with silk and green when viewed perpendicular to the crystal axis, features taken to suggest appreciable iron content. Their satellite reflections occupied alternate arms of a bronze-coloured star. A pale-blue exception displayed a diffuse white star with the three reflections positioned between its arms. Detailed examination of a twelve-rayed specimen identified two inclusion systems producing white and bronze six-rayed stars rotated approximately 30° relative to each other. The white system consisted of fine, long, relatively colourless needles resembling rutile, while the bronze system comprised shorter, tapering, blade-like inclusions concentrated in bands associated with hexagonal or chevron zoning. Some bronze blades showed interference colours consistent with very thin platelets. An iron-rich, titanium-depleted ilmenite-related phase, discussed in connection with previous work on ferrilmenite, is proposed for the bronze silk. The article documents the geometrical relationships between the stars, satellite reflections and host-crystal symmetry, while presenting the identities and formation mechanisms of the responsible inclusions as hypotheses requiring further confirmation.

corundum, synthetic corundum.7, gems

Discusses seven misconceptions about flux-grown synthetic rubies from the perspective of a partner in the J.O. Crystal Company, producer of Ramaura ruby. The author first rejects the assumption that laboratory growth permits unlimited control over crystal size, clarity, variety and cost, stressing that synthesis remains constrained by physical laws and practical growth conditions. Inclusions are not deliberately inserted to imitate natural ruby: trapped flux, internal fractures, fingerprints and feathers arise during growth, and the producer seeks to minimise them because cleaner material commands higher prices. The article distinguishes the implications of the terms laboratory-grown, flux-grown, created and cultured, explaining the company’s preference for “cultured” as a description of crystals grown from a nutrient solution with human involvement. It contrasts flux growth with inexpensive, high-volume flame-fusion production and argues that the two products differ substantially in appearance and manufacturing cost. Carter attributes Ramaura ruby’s natural-looking appearance to slow precipitation from a supersaturated solution, spontaneous nucleation without a seed, and a relatively regular crystal lattice with few dislocations. Addressing fears that synthetic stones will overwhelm the market, she states that annual flux-grown ruby and emerald production amounts to no more than approximately 1% of the number of newly mined and faceted natural counterparts, and that difficult, costly production prevents supply from meeting demand. Particular attention is given to the identification dopant intentionally incorporated into every marketed Ramaura ruby. According to the author, this shifts long-wave ultraviolet fluorescence towards yellow-orange relative to natural ruby; its effect varies with the dopant concentration prevailing when individual crystals form. Examination should therefore take place in a darkened room, using a long-wave ultraviolet lamp and direct comparison with a natural ruby. The company describes doping as a voluntary measure intended to preserve reliable distinction from natural material. Finally, the article explains why synthetic origin does not imply negligible value: high-purity platinum crucibles, months of furnace operation, substantial electricity consumption and low cutting yields all contribute to cost. Reported prices range from US$50–350 per carat according to size and grade, or approximately 5–10% of the price of comparable natural ruby. Company and partner biographies provide context for these explanations and the commercial position from which they are presented.

gems, spinel, Tanzania, spinel inclusions

A brief gemological report on spinels from Tanzania’s Umba Valley, occurring in pink, red, orangish red and bluish violet colors. The specimens examined had refractive indices of 1.713–1.718 and specific gravities of 3.54–3.69. Spectroscopic examination was used to investigate the causes of the different colors. The note documents the range of gem spinel then reaching the market from the Umba Valley and provides basic properties useful for characterizing this East African material.

corundum, sapphire, Kenya.12, Turkana, asterism, inclusions.5, gems

Examines cabochon-cut sapphires from northwestern Kenya to characterise their inclusions, explain their asterism and distinguish them from synthetic star sapphires. Material entering the Kenyan market from mid-1987 was collected from superficial secondary deposits west of Lake Turkana, although its primary geological source remained unidentified. Ten cabochons, ranging from blue and greenish blue to greenish yellow and dark brown, were investigated using conventional gemmological testing, optical microscopy, electron-microprobe analysis and X-ray diffraction. Eight displayed six- or twelve-rayed asterism of varying quality, while two showed concentrated silky areas rather than a complete star. Some specimens produced exceptionally sharp, evenly developed six-rayed stars resembling those of Linde synthetic sapphires. Refractive-index measurements gave an approximate value of 1.765, and the stones were inert under long- and short-wave ultraviolet radiation. Visible absorption commonly showed iron-related features near 450, 460 and 470 nm. Microscopic examination documented cloudy areas, acicular structures, rutile silk, tubular cavities, transparent crystals, fluid feathers and healed fractures. The structures associated with asterism were separated into microstriae compositionally similar to the sapphire host and distinct needle-like inclusions interpreted as rutile or hematite. Their crystallographically controlled orientations and variable distribution were considered responsible for differences in star development. Rutile was supported by weak reflections in bulk X-ray diffraction patterns. Darker colours were associated with iron-rich inclusions, including hematite needles and iron oxide or hydroxide material occupying channels and healed fractures. Transparent, low-relief hexagonal crystals were assigned to corundum, while reddish-brown prismatic titanium-rich inclusions were interpreted as rutile. Straight-edged colour bands and angular growth zoning record successive growth episodes and changing chemical conditions. Together with the absorption spectrum, these features help distinguish the natural material from synthetic star sapphire despite similarities in the appearance of the stars. The authors reconstruct an initial history of crystal growth and inclusion formation followed by fluid penetration, fracture healing and deposition or transformation of iron compounds. They suggest that some iron hydroxides subsequently dehydrated to oxides as temperature increased. Mineral-equilibrium considerations are used to propose high-temperature, high-pressure growth, with maximum crystallisation temperatures exceeding approximately 500 °C. The study links the stones’ optical effects to their internal structures while leaving their precise primary occurrence unresolved.

corundum, inclusions.5, Sri Lanka.12, geology.11, gems

Mineral and fluid inclusions were studied in seven gem corundums from gravels of three areas in Sri Lanka. All fluid inclusions are pure CO2. Microthermometry results on primary fluid inclusions suggest formation of corundum under granulite facies metamorphism (>630 ~ 5.5 kbar). Secondary fluid inclusions indicate different retrograde events of post-metamorphic cooling and uplift for different source areas.

corundum, Australia.12, color.4, gems

G. Brown and S.M.B. Kelly describe an unusual apparent colour change in a natural sapphire from the Central Queensland sapphire fields, attributing the effect to the interaction of illumination with strongly zoned colour rather than to a true alexandrite effect. The specimen is a 2.03 ct oval brilliant that appears bluish in daylight and colour-corrected fluorescent light but purplish under incandescent illumination. Routine testing gives a hardness of 9, specific gravity of 3.98, refractive indices of 1.762 and 1.770, and birefringence of 0.008. Pleochroic colours are blue and reddish blue, the Chelsea-filter response is blackish, and no visible absorption features are reported. Examination also reveals a conspicuous orange patch within the otherwise predominantly blue sapphire. Microscopy establishes that this patch is discrete and closely associated with angular colour banding, readily seen when the stone is viewed obliquely through its crown. Rounded inclusions tentatively identified as zircon are scattered throughout the specimen and are surrounded by disc-like stress halos. Dust-like silk is prominent around both the angular zoning and the orange region. A particularly bright, irregularly outlined disc proves to be reflected light from a stress halo surrounding one of the presumed zircon crystals, rather than a separate reflective inclusion. Experimental illumination shows that the apparent colour depends on both the direction of incident light and its spectral composition. In blue-green-rich daylight, or when light passes through the major blue component of the stone, the sapphire appears blue. Under red-rich incandescent light, or when illumination is deliberately directed through the orange patch, it becomes reddish blue or dark purplish blue. Illumination from two separate directions can also produce a visibly bicoloured appearance. The authors locate the orange zone deep within the pavilion and regard it as the apparent control on the observed change. They therefore distinguish the specimen’s initially alexandrite-like appearance from a true alexandrite effect, explaining the observation in terms of differently coloured regions contributing unequally under changing lighting conditions. Photographs document its contrasting appearances, colour zoning, inclusions, and directional response. The report presents the stone as an exceptional example of colour-changing behaviour in Central Queensland sapphire while emphasizing the need to examine internal zoning and illumination geometry when interpreting such effects.

corundum, color.4, gems

The expanding role of recording spectrophotometers in gem identification is illustrated through the development of the Gem Testing Laboratory of Great Britain’s equipment and several diagnostic case studies. Although the hand-held spectroscope remains valuable, its limitations become significant when precise wavelength measurements, absorption-band shapes, or information outside the visible region are needed to distinguish synthetic gems and treated natural material. Diamond absorption features provide an example: the H3 zero-phonon line at 503.2 nm and the H4 line at 496 nm require careful distinction because an H3 phonon sideband can be mistaken for the latter, potentially affecting interpretation of color origin. Cooling diamonds to approximately 120 K improves visual resolution, but recording instruments provide more complete spectral information. The laboratory initially acquired a Pye Unicam PU 8800 ultraviolet-visible spectrophotometer and subsequently added a Nicolet 510 Fourier-transform infrared spectrometer as infrared analysis became increasingly important. Guidance is given on interpreting absorbance and transmittance curves and relating recorded features to observations through a hand spectroscope. Examination of De Beers synthetic yellow to greenish yellow and brownish yellow diamonds combines ultraviolet luminescence, growth-sector zoning, metallic and dust-like inclusions, and infrared spectra. The examined synthetic stones show isolated-nitrogen absorption characteristic of type Ib diamond without aggregated-nitrogen features, whereas a natural yellow type Ib comparison stone also contains an aggregated-nitrogen peak. Infrared spectroscopy also identifies amber in mounted earclips and beneath artificial coatings on beads when conventional tests are restricted by mounting or surface treatment. The earclips display colored outer layers surrounding colorless interiors, consistent with heat treatment; the beads have an additional orange artificial coating over a yellow surface layer. A further case concerns a 5.80 ct diamond whose appearance varies among green, gray, and brown under different lighting. Its visible spectrum does not fit a straightforward conventional category. Strong blue-green phosphorescence following short-wave ultraviolet exposure and electrical conductivity suggest type IIb diamond, and comparison of its infrared spectrum with recorded reference spectra confirms that classification despite its atypical color. These examples demonstrate how instrumental spectroscopy complements microscopy and routine gemological observations, providing decisive information in cases where appearance or simpler tests are insufficient. The article argues that increasing identification challenges justify advanced instrumentation and that clearly presented spectral curves remain accessible and useful to practicing gemologists.

corundum, Inclusions.5, Burma.12, gems