corundum, inclusions.5, gems

The first substantiated identification of corundum (var. ruby) occurring as an inclusion in natural diamond is presented. The ruby is assigned to the eclogitic suite of inclusions in diamond, and the implications of its occurrence are discussed in relation to the genesis of “eclogitic” diamonds. It is concluded that diamond crystallizes from a melt over a long period of time with possible fluctuations in ambient temperature and geochemical environment.

beryl, inclusions, gems

Mineral inclusions in colourless, greenish and bluish beryls from Brazil, Afghanistan, Kenya and Switzerland reveal recurring assemblages that illuminate the pegmatitic environments in which their hosts formed. Microscopic observations, electron-microprobe analyses of inclusions exposed at polished surfaces, and selected X-ray examinations establish several combinations of mica, manganese-bearing minerals and niobium–tantalum oxides. A Brazilian goshenite contains a large brown phlogopite crystal associated with silvery muscovite flakes and metallic black columbite, termed niobite in the paper. A second Brazilian specimen contains a comparable association together with a dark green, barrel-shaped manganese-bearing apatite crystal. In pale blue aquamarine from Nuristan, Afghanistan, brownish isometric inclusions were identified repeatedly by microprobe analysis as spessartine. An accompanying large colourless crystal, initially resembling apatite because of its apparent hexagonal form and parallel cleavage planes, was identified optically as pseudohexagonal muscovite. The most diverse assemblage occurs in greenish-blue aquamarine from Kenya and includes conspicuous albite clusters, orange spessartine, phlogopite, and columbite–tantalite minerals. Microprobe results distinguish niobium-rich tabular inclusions from tantalum-rich acicular crystals. Small green inclusions were exposed by cutting down the host’s basal surface, and extracted fragments examined with a Gandolfi X-ray camera were identified as dravite tourmaline intimately associated with gahnite. The author presents this tourmaline–gahnite association as previously unrecorded within beryl. A Swiss aquamarine contains an orange crystal with characteristic garnet morphology, interpreted as spessartine; this identification was accepted without destructive exposure or chemical analysis to preserve the specimen. An additional aquamarine, not illustrated, contains lithium-rich mica associated with columbite. The repeated occurrence of related inclusions in beryls from widely separated localities indicates similarities in their mineral-forming environments. Columbite is considered especially informative because of its association with manganese-rich granitic pegmatites containing abundant albite and lithium minerals. Such conditions also account for accompanying spessartine and manganese-bearing apatite. Large pseudohexagonal mica crystals with prominent basal cleavage provide a particularly recognizable internal feature. The study demonstrates the value of combining inclusion morphology and optical behaviour with chemical and crystallographic evidence, both to distinguish visually similar guest minerals and to interpret the growth environment of their beryl hosts.

corundum, sapphire, Sri Lanka.12, treatments.6, gems

Examines the commercial heat treatment of Sri Lankan geuda corundum and considers the origin of its colour response and possible criteria for recognising treated stones. Gunaratne places this development within the established practices of heating ruby to reduce purplish tones and heating dark or unevenly coloured sapphire to improve appearance. Geuda is described as a milky, opalescent condition associated with abundant inclusions, particularly rutile, which had formerly reduced the commercial value of the rough. Its successful conversion into blue sapphire transformed demand, initially through extensive treatment in Thailand and subsequently through growing activity in Sri Lanka. Rough selection is presented as crucial: favoured material combines a faint powder-blue tint, milky sheen and honey-like transmitted appearance, locally termed diesel geuda. Fractures, fluid inclusions and other potentially damaging features influence suitability, while different grades require different treatment conditions. Gas-, diesel- and electrically heated furnaces are described as producing comparable transformations, with heating duration adjusted to the material and temperatures achieved. The author proposes that differences in the origin and crystallisation history of rutile help explain variable treatment responses, linking intense heating to redistribution of titanium-related colouring constituents within the host. These explanations are offered as theoretical interpretations requiring further investigation rather than results of controlled chemical experiments. Examination of successfully treated stones reveals diffuse or blotchy colour zoning, reduced sharpness of growth lines, occasional woolly white patches and healed fractures. Zircon inclusions and fissure stains were absent from the examined material, although their absence could reflect selection of the original rough. Most specimens were inert under short-wave ultraviolet radiation; only four deep-blue polished stones in a selected group of one hundred rough and polished samples showed a powder-blue glow. Some stones exhibited dirty brown to brownish-red luminescence under long-wave ultraviolet radiation. Optical and physical constants and handheld absorption spectra remained comparable with untreated sapphire, limiting their diagnostic usefulness. The paper calls for nondestructive identification methods, systematic comparison of stones before and after heating, and investigation of the critical temperatures governing colour development. Its conclusions are explicitly limited by reliance on commercially treated, successful products and insufficient examination of untreated starting material or failed treatment outcomes.

corundum, sapphire, star sapphire, inclusions.5, star quartz, gems

Weibel, Wessicken, Woensdregt, and Wüthrich examine the optical mechanism responsible for chatoyancy and asterism, with particular attention to black star sapphire from southeastern Thailand and milky-white star quartz from Ratnapura, Sri Lanka. They explain that each ray of a star results from light scattering by a set of parallel fibrous structures within the crystal, with refraction at the curved cabochon surface also contributing to the observed effect. Contrary to the usual explanation involving rutile silk, electron microscopy revealed no inclusions in the Thai black star sapphire; its fracture surfaces instead show stepped structures with trigonal dislocations, and the authors suggest regular lattice dislocations or twinning as possible causes of the asterism. In the Ratnapura star quartz, electron diffraction identifies the scattering needles as sillimanite, averaging about 0.02 μm thick, rather than rutile; their imperfect orientation accounts for the diffuse and incomplete star.

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.

corundum, quality.10, gems

A practical guide to buying, selling, evaluating, and investing in precious gemstones, written by New York gem dealer Benjamin Zucker. Originally published in 1976 as How to Invest in Gems, this revised second edition reflects the dramatic increases in gemstone prices during the late 1970s and advocates fine rubies, sapphires, emeralds, and diamonds as long-term investments and hedges against inflation and currency depreciation. Individual chapters examine the geological occurrence, mining, cutting, identification, quality factors, geographical origins, and market values of the four principal gemstones, with particular attention to color, clarity, size, and inclusions. Ruby sources discussed include Burma, Sri Lanka, Thailand, Cambodia, Afghanistan, and Kenya; sapphire sources include Kashmir, Burma, Sri Lanka, Thailand, Australia, and Montana; and emerald sources include Colombia, Brazil, Rhodesia, Zambia, Afghanistan, and others. Zucker describes methods of distinguishing natural from synthetic gemstones using microscopy, refractive index measurements, ultraviolet fluorescence, and characteristic inclusions, drawing upon the research of Eduard Gübelin and other gemologists. A substantial section examines the history and operations of De Beers, including its control of diamond production and distribution, relationships with Soviet producers, and methods of stabilizing diamond prices. Other chapters address gem appraisals, auctions, retail and wholesale pricing, and the investment potential of tourmaline, garnet, aquamarine, and other gemstones. Suggested investment portfolios range from $10,000 to $1 million, with recommendations concerning gemstone varieties, sizes, and qualities. Appendices provide comparative gemstone prices from 1968 to 1979, descriptions of major museum collections, an overview of gemological institutions and grading systems, and historical accounts of jewelry craftsmanship, Fabergé, Marco Polo, and Louis XIV. Particularly interesting are the author's firsthand account of purchasing a 94 ct blue star sapphire subsequently exhibited at the American Museum of Natural History and his descriptions of the Iranian Crown Jewels. Illustrated with numerous color and black-and-white photographs of gemstones, inclusions, mining operations, jewelry, and museum treasures, the book offers a revealing contemporary perspective on the international gemstone trade and investment philosophy of the late 1970s, although its price information and some gemological interpretations are now dated.

amber, inclusions, gems

gems, fluorite, inclusions in fluorite

Illustrates characteristic inclusions in fluorite through colour photographs, including green chlorite crystals, secondary liquid inclusions, three-phase inclusions and well-formed pyrite crystals.

quartz, topaz, inclusions, gems

Reports microthermometric observations of fluid inclusions in an amethyst of unknown origin and a blue topaz from St Anne’s Mine, Miami, Zimbabwe, extending an earlier study of comparable inclusions in amethyst. Both specimens contain primary negative crystals and irregular inclusions interpreted as pseudosecondary, with liquid and vapour phases occurring in varying proportions. In the amethyst, primary cavities are aligned parallel to the host’s c-axis. After cooling to −150 °C, subsequent warming reveals a phase change described as sublimation at −108 °C in the primary inclusions, followed by ice melting at −1.6 °C; ice in the pseudosecondary inclusions melts at −0.2 °C. The latter homogenise between 153 and 170 °C. Comparison with the previously examined amethyst reveals broadly analogous behaviour, which Gübelin interprets as indicating a common source. He infers water-bearing primary inclusions at low internal pressure and weakly saline aqueous fluid in the pseudosecondary inclusions. Necking down limits the precision with which homogenisation temperatures can be related to formation conditions. A proposed model places amethyst crystallisation in cavities within volcanic rocks, from hydrothermal solutions at approximately 150–200 °C and 20–30 bar. Boiling and entrapment of vapour are invoked to explain some cavities, with an additional gas, possibly carbon dioxide, tentatively suggested. The topaz was cooled to −180 °C and warmed while changes in its inclusions were observed. Ice begins melting near −2 °C, some daughter crystals dissolve between 20 and 100 °C, and many remaining solids dissolve by 232 °C. Heating was stopped at that temperature to avoid cracking, so the proposed homogenisation temperature near 250 °C was estimated rather than measured. Repeated cooling and warming demonstrate spontaneous nucleation and growth on existing crystals. The author interprets the topaz as hydrothermal, consistent with field observations, but notes that the inferred temperature is unusually low compared with published values. Its inclusions appear highly saline, although the salts remain unidentified; their optical behaviour and limited depression of the ice-melting temperature lead him to suggest sulfates rather than chlorides. The interpretations are explicitly presented as working hypotheses requiring further investigation with more abundant material.

inclusions, crystal angles, gems