gems, garnet, grossular, hessonite, India, Orissa, tourmaline, sillimanite

The state of Orissa in eastern India has emerged as an increasingly important source of gemstones. Since 1989, rising quantities of rhodolite garnets from the region have been seen, followed by notable finds of aquamarine and ruby. At the 1993 Tucson Show, Amar J. Jain presented a 2.99 ct faceted alexandrite and dark grayish blue tourmalines from Orissa, one of which—a 1.74 ct emerald-cut specimen—showed gemological properties consistent with tourmaline from other locations, including refractive indices of 1.620 and 1.640, birefringence of 0.020, and specific gravity of 3.11. Hessonite (grossular) garnet is also being mined near Kanta Bhaji in the Kalahandi area, with faceted stones ranging from reddish orange to orangish brown; many exhibit a pronounced “roiled” appearance typical of Sri Lankan hessonites, sometimes resembling translucent sard. A 2.19 ct orange stone tested with an R.I. of 1.748 and S.G. of 3.65, confirming it as hessonite. Following the show, the editors received a report from Shyamala Fernandes of the Gem Testing Laboratory in Jaipur describing a December 1992 find of chatoyant sillimanite, initially misidentified and marketed as “moonstone cat’s-eye.” Identified as sillimanite, the material exhibited an R.I. of 1.659–1.678 (1.66 spot), S.G. of 3.25, biaxial optic character, and Mohs hardness of 7–8. Microscopy revealed parallel acicular inclusions responsible for the chatoyancy, along with “fingerprint” two- and three-phase inclusions and black platelets. The sillimanite occurs in colors ranging from colorless to gray, pinkish brown, yellow, green, and blue-green, typically in lighter tones, and most cabochons—some up to 20 ct—display sharp cat’s-eyes and a vitreous luster. Though precise production data is lacking, the material has been readily available in Indian markets since its discovery.

corundum, inclusions.5, gems

corundum, synthetic corundum.7, hydrothermal, Russia, color.4, gems

Three synthetic rubies marketed in Bangkok in January 1993 as hydrothermal products from Novosibirsk, Russia, were examined to establish characteristics useful for distinguishing them from natural ruby and other synthetic rubies. The faceted samples weighed approximately 0.62, 0.69, and 1.69 ct and displayed highly saturated red colors with medium to dark tones, resembling ruby from Thailand and Myanmar. Standard properties, including refractive indices, birefringence, specific gravity, pleochroism, ultraviolet fluorescence, and visible absorption spectra, broadly overlapped those of other natural and synthetic rubies. Their most conspicuous feature was strong internal graining that slightly reduced transparency and imparted a sleepy appearance. The graining appeared striated in most viewing directions and strongly roiled when viewed parallel to the basal growth plane; one specimen also displayed an unusual Christmas-tree pattern of uncertain origin. Color fluctuations followed these irregular growth structures rather than the planar or swirled zoning familiar in other rubies. Numerous highly reflective golden inclusions occurred as isolated platelets or small groups. Electron-microscope analysis identified two copper-rich inclusion types: one containing minor iron, nickel, and titanium, and another containing iodine and sulfur. No gold or platinum was detected. A slender, colorless needle-like feature was also observed, although its identity as a solid inclusion or negative crystal remained unresolved. Transparent fingerprint-like healed fractures, occasionally containing gas phases, resembled those in natural ruby and could complicate identification. Analysis of one surface-reaching healed fracture detected none of the lead, molybdenum, bismuth, or tungsten expected from certain flux residues. Chemical analyses showed chromium, iron, titanium, copper, and nickel, with vanadium and gallium absent or present only at very low concentrations. Iron contents were comparable to those of iron-rich natural rubies but higher than those previously observed by the authors in other synthetic rubies. The reported hydrothermal origin was consistent with the observations but remained unverified. Possible growth conditions, contamination from autoclave components, and the likely use of seed crystals are discussed as interpretations requiring further investigation. The distinctive graining and metallic inclusions provide practical identification criteria, although the latter could be mistaken for natural sulfides. Where microscopy is inconclusive, chemical analysis of the host and inclusions offers additional evidence for separation. Further study of rough crystals and fluid inclusions is recommended to clarify the growth process.

corundum, synthetic corundum.7, hydrothermal, Russia, color.4, gems

Until now the commercial production oi synthetic mby has consisted of two may or types of synthesis, the flame-fusion and flux-growth processes, even though the techniques for a third type involving the hydrothermal growth of synthetic rubies have been known since the late 1950's. The early hydrothermal ruby production was reported as consisting of thin overgrowths on natural ruby seeds (C ubelin, 1961 'l. The authors first became aware of the recent production of hydrothermal synthetic rubies in Novosibirsk during the Fall of 1991. In lanuary 1993, synthetic rubies described as hydrothermal” synthetic rubies produced at Novosibirsk first began appearing on the market in Bangkok (including the samples in this study, weighing 1.69, 0.69 and 0.62 Cl). The hydrothermal growth process is often responsible for the formation of ruby in natural deposits worldwide, excluding those resulting from magmatic melts. Therefore, it can be expected that the internal characteristics for hydrothermally grown synthetic rubies will include the presence of fluid inclusions comparable to those oi their natural counterparts as opposed to the flux remnants present in the healed fracture systems of other synthetic rubies. This could create potential problems in the separation between natural and synthetic rubies. The aim of this study is to provide the identification characlenstics and results of standard gerrimological as well as more sophisticated testing."

gems, diamond, North Africa, Algeria, Sahara, Bled-el-Mass Valley

Diamonds and the indicative minerals (pyrope, picroilmenite, and chromite) are found on a vast area of submeridional elongation of 300 km of the Reggan district in the Algerian Sahara. The Bled-el-Mas ancient valley is in its centre, and here Late Pleistocene alluvials and proluvials are diamondiferous. Diamonds are represented by octahedral, dodecahedral and transitional colorless and yellowish crystals with chromite, graphite and other mineral inclusions. Among the pyropes the knorringite-containing varieties of diamond association is found. As an intermediate diamond source the Early Cretaceous conglomerates are regarded, while their primary source has not yet been established.

gems, garnet, almandine, Egypt, Greco-Roman jewelry, ancient jewelry

During a 1991 visit to Egypt, a Gem News editor observed gem-set antiquities in the Egyptian Museum in Cairo, including dark brownish red stones in Greco-Roman jewelry that resembled almandine garnet. A museum chart listed garnet among the materials used by ancient Egyptians, though without specifying species. Later, in Luxor, the editor encountered a necklace of similarly colored beads from a gem dealer, who claimed they were garnets sourced from the south-central Sinai Peninsula, near Gebel Musa (Mt. Sinai), though the exact mine location was lost. John D. Rouse, in Garnet, referenced Pliny’s mention of Egypt as a source of “carbuncles,” likely garnets, possibly originating from a Theban trading station rather than a mine. The necklace, acquired for gemological study, comprised 36 off-round beads, 12.3–13.0 mm in diameter, appearing brown and opaque in reflected light but brownish red and transparent in transmitted light. Magnification revealed dark inclusions and stained fractures. Spot refractive index readings exceeded 1.80, and spectroscopic analysis showed absorption features typical of almandine and spessartine. EDXRF analysis confirmed the presence of iron and manganese, leading to the identification of the beads as almandine–spessartine garnets.

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

Lamellar inclusions in gem spinels reportedly originating from the Morogoro area of Tanzania are identified as an iron-free, titanium-rich member of the högbomite series. The investigation concerns rough and faceted material obtained through several independent trade sources following the first receipt of samples in June 1987. The crystals include red, pink, orange, reddish purple, purplish blue and blue octahedra reaching approximately 1 cm. Most suppliers independently reported Morogoro as the source, and the occurrence of similar inclusions across the parcels supported a common locality; an earlier attribution to the Umba Valley was therefore considered probably incorrect. Conventional physical properties, trace-element compositions and absorption spectra did not distinguish these stones significantly from natural spinels from Sri Lanka and Myanmar. Their colour-related absorption was attributed to chromium, vanadium, iron in different valence states and cobalt, with cobalt detected by X-ray fluorescence despite concentrations below the electron microprobe detection limit. In contrast, approximately 70% of the examined Tanzanian samples contained characteristic lamellar inclusions. These occur in four orientations parallel to the octahedral {111} faces of the spinel host. Viewed along a ⟨110⟩ direction, two sets intersect at angles of 109.47° and 70.53°. Immersion microscopy with crossed polarizers established that the lamellae are doubly refractive. Their extreme thinness prevented successful identification by electron microprobe, but transmission electron microscopy of ion-beam-thinned petrographic sections resolved their structure and composition. Individual lamellae measured 0.01–0.1 µm thick. Electron diffraction indicated trigonal, rhombohedral symmetry, with unit-cell dimensions of approximately a = 5.7 Å and c = 55.8 Å. Quantitative energy-dispersive X-ray analyses using a 15 nm electron probe identified magnesium–aluminium–titanium oxides, supporting their assignment to iron-free, titanium-rich högbomite. The structural relationship between högbomite and spinel is discussed in terms of titanium substituting for magnesium, with related structures also occurring in taaffeite and musgravite. The authors propose these oriented, birefringent inclusions as a practical indication of natural Tanzanian spinel, potentially useful in distinguishing such material as flux-grown synthetic spinels become increasingly available.

corundum, ruby, sapphire, Kenya.12, Tanzania.12, East Africa, geology.11, gems

An illustrated survey of East African gemstones, emphasizing the deposits of Kenya and Tanzania and combining regional geology with accounts of discovery, exploration, mining, and gemological properties. Following an introduction to the geological setting, Keller discusses diamonds, ruby and sapphire, emerald and alexandrite, tanzanite, garnets, tourmaline, and green opal, with a concluding chapter on less prominent gem materials. Individual accounts place the deposits within their geological environments while recording their development and the people involved. Particular subjects include tanzanite from Merelani and prase opal from Haneti Hill, Tanzania. Photographs of rough and cut stones, inclusions, mining operations, and historical scenes complement locality maps, including some previously unpublished examples. Contributors include E.J. Gübelin, Harold and Erica Van Pelt, and J.I. Koivula. Appendices list 177 noteworthy gem localities with geographical coordinates and document East African gemstones in the collections of the Los Angeles County Natural History Museum and the Smithsonian Institution. References accompanying each chapter provide access to the region’s geological and gemological literature. The volume offers a substantial record of East African gem deposits and industry as understood at the beginning of the 1990s.

corundum, chemistry.2, inclusions.5, geology.11, Australia.12, gems

R.R. Coenraads examines the surface morphology of natural rubies and sapphires from volcanic-associated placer deposits in eastern Australia and Thailand, distinguishing features inherited from crystal growth and magmatic transport from damage acquired in alluvial environments. Samples from the New England gemfields and the Bo Phloi and Chanthaburi–Trat districts were studied with binocular microscopy, followed by scanning electron microscopy of selected cleaned and gold-coated specimens. The observed features fall into three broad categories: negative crystal impressions, resorption and etching structures, and fractures or impact damage associated with subsequent transport. Deep, sharply bounded geometric sockets are interpreted as impressions left by neighbouring minerals in a coarse crystalline aggregate containing corundum, anorthoclase, zircon, and spinel. Coenraads proposes that corundum-bearing assemblages formed from evolved, silica-poor magmas and were subsequently disaggregated and partly dissolved by alkaline basaltic carrier magmas during ascent. Most rounded surfaces are attributed to this magmatic resorption rather than prolonged stream wear. Their sculpturing reflects corundum’s trigonal symmetry and varies with surface orientation relative to the c-axis. Features include triangular prismatic hillocks, pyramids, inverted pyramidal pits, and shallow triangular or hexagonal depressions containing central remnants. Surfaces approximately parallel to the c-axis may display inclined stacks resembling elongated triangular bricks, while intermediate orientations favour triangular pyramidal depressions. Continued dissolution enlarges and merges these structures into irregular channels, porous textures, and deeply sculptured surfaces. Fine corrosion pits and microscopic steps indicate superimposed etching and successive layer removal. Curved or subparallel chatter marks are interpreted as products of mechanical stress; crystallographically controlled etching within them suggests that they formed before or during magmatic ascent and were subsequently modified by dissolution. Later mechanical damage includes conchoidal fractures radiating from impact points, chipped edges, and broken hillocks exposing clean fracture surfaces. Breakage along previously healed or partly healed fractures can reveal fingerprint-like networks of fine tubes, connecting external surface observations with familiar internal inclusions. Despite these examples of damage, many delicate surface projections remain intact. Their preservation, considered alongside spatial differences in corundum characteristics within individual placers, indicates limited downstream reworking and mixing. Coenraads concludes that the sources are likely to lie close to the placer deposits. The study demonstrates how successive generations of surface features can preserve evidence of crystal association, reaction with carrier magma, stress, and fluvial history, allowing rounded gem corundum to be interpreted through processes more specific than abrasion alone.

gems, spinel, star spinel, Sri Lanka

Recent developments in Sri Lankan gemstone production are summarised from information supplied by dealer Gordon Bleck, with particular attention to unusual materials and newly reported occurrences. Mining was reportedly being hindered by terrorist activity, especially in remote jungle areas around Okampitiya, while Ratnapura remained relatively safe. Rubies from a newly reported locality near Hambantota were described as unusually good in quality and deeper in colour than material generally associated with Sri Lanka, although individual stones rarely reached one carat. Deep pink fancy sapphires had also been found in the Matara district on the southern coast, but production was limited and fashioned stones seldom exceeded two carats. A notable departure from previously encountered Sri Lankan star spinel was the discovery in the Ratnapura district during 1991 of saturated red material with a high degree of transparency. Earlier examples familiar to the editors had generally been almost opaque, very dark, and weakly saturated purple. A photographed 1.12-carat red star spinel illustrates the distinctive combination of colour, transparency, and asterism. Other reported finds included clean, light yellow danburite from the Nirialla River, approximately ten kilometres from Ratnapura near Palawela and Nirialla. A large river-bed specimen yielded an 11.52-carat pear-shaped gem, while smaller fragments came from the river bank; this newer production was less included than earlier material. Two translucent yellowish green andradite crystals were among the year’s rarities, the larger measuring about two centimetres across and showing combined dodecahedral and trapezohedral forms. Increased quantities of colour-change spinel, sapphire, and garnet were also reported. Facetable kornerupine had become more available, including a 17.01-carat brownish green stone from central Sri Lanka whose unusually light tone was noteworthy for its size, whereas cat’s-eye kornerupine had become scarce. An unusually large, 5.00-carat blue sillimanite from Ambalapitiya completed the selection. The report documents the diversity of the country’s gem output through specific examples, emphasising differences in colour, transparency, size, inclusion abundance, and availability.