corundum, Australia.12, treatments.6, gems

gems, fluorite, inclusions in fluorite, fluid inclusions

Several fluorite ± barite mineralizations, mainly controlled by post-Pliocene disjunctive faults, occur in silicified and altered Mesozoic limestones in the area of Termini Imerese (NW Sicily). In this study, we examined fluid inclusions in fluorite from the localities of Rocca Grande and Poggio Balate. Fluorite from both localities contains abundant two-phase liquid-rich aqueous inclusions. Less common types are: (a) monophase (liquid or gas); (b) two-phase, mostly gas-rich, hydrocarbon inclusions; (c) three-phase (liquid + gas + an accidentally trapped solid); and (d) three-phase (gas + two liquids: an aqueous brine and a hydrocarbonic fluid). In many inclusions, the presence of gas under pressure (most probably methane) is revealed by crushing tests. Homogenization temperatures (Th) of aqueous inclusions spread over a large range (60° to over 300 °C), being on average higher at Rocca Grande (∼200 °C) than at Poggio Balate (∼150 °C). Pressure corrections to Th are presumably minimal. However, several factors concur in suggesting that most Th’s are probably too high with respect to true trapping temperatures. Tentatively, the lowest Th-values (∼100 °C at Poggio Balate, and ∼150 °C at Rocca Grande) may be taken as indicative of trapping conditions. Temperatures of final melting of ice are, with few exceptions, higher than −3 °C. The geological setting and previous geochemical studies suggest that the fluorite-forming fluids were essentially heated meteoric waters. This is in agreement with the low salinities of most inclusions. On the other hand, reconnaissance δD determinations on bulk sample inclusions (‰ vs. SMOW) may reflect minor contributions of seawater to the hydrothermal fluids. The presence of abundant oil and methane is ascribed to interaction with organic matter-rich beds occurring in the local stratigraphic sequence.

corundum, inclusions.5, microscope, gems

The eyepiece pointer is a highly useful microscope accessory for the gemologist, as it remains in focus and consistently indicates the center of the microscope’s field of view regardless of magnification or the focal plane within the gemstone. It greatly simplifies the task of identifying and showing microscopic features in both mounted and unmounted gems, and it can be easily adapted for use with nearly any microscope.

corundum, ruby, sapphire, Sri Lanka.12, inclusions.5, gems

tourmaline, gems

A comprehensive synthesis of tourmaline mineralogy and gemology, drawing on more than 2,500 publications and incorporating nearly 1,000 references. Dietrich examines nomenclature, crystal morphology and structure, chemical composition, and the relationships between chemistry, species classification, and physical properties. Coverage includes crystal habits, exceptionally large crystals, inclusions and intergrowths, causes of color, color patterns, pleochroism, luminescence, and the effects of heating and irradiation. Additional chapters address physical properties, laboratory synthesis, industrial applications, and recovery. The gemstone chapter discusses tourmaline’s historical use in jewelry and decorative arts, fashioning, and notable gems. Geological coverage considers occurrences and formation in igneous, metamorphic, and sedimentary environments, while an appendix lists important sources of mineral specimens and gem material worldwide. The work’s principal strength is its organized compilation and evaluation of a widely scattered literature, making it useful to mineralogists, gemologists, and collectors. Individual deposits receive limited treatment, however, and the locality appendix lacks references directing readers to detailed accounts.

Thailand.12, Bo Ploi, blue sapphire, inclusions.5, corundum, gems

Gunawardene and Chawla describe the sapphire deposits of Bo Phloi, Kanchanaburi Province, western Thailand, a locality that had become an important source of commercial blue sapphire during the preceding decade. The paper gives details of the locality and its accessibility and reviews geological investigations of Kanchanaburi, comparing the occurrence with the better-known basalt-associated gemfields of Chanthaburi–Trat in eastern Thailand. The authors present chemical and physical data for the sapphires and grade their colours using the DIN colour system. Particular attention is given to microscopic examination: characteristic internal features are illustrated with photomicrographs and analyzed for their value in characterizing Kanchanaburi material. The study provides an early detailed gemmological description of sapphires from this important Thai basalt-related deposit.

corundum, Sri Lanka.12, gems

As known to the gemmologist and jeweller, East Africa's famous gem locality, Tanzania, is well known not only for garnets of various colour varieties, but also for corundums of many colours and hues. The occurrence of corundum in Tanzania is reported by many researchers (Zwaan, 1974; Dolenc, 1976; Amstutz & Bank, 1977; Bank, 1978). However, these reports mainly describe the common corundum varieties such as ruby and blue and yellow sapphires. Recent observations made by the author on new occurrences of sapphires from Umba Valley revealed a reddish-brown colour variety which has often been termed as 'padparadschah* in the trade. It therefore became necessary to investigate systematically the differences between the 'real' padparadschah and this new occurrence. The chemical and physical properties of the latter are given with special emphasis on the cause of colour. Further, the inclusions are reported, which may be of help in documenting the locality.

Pakistan, pink topaz, gems

Gübelin describes gem-quality rose to pink topaz from the Katlang area, northeast of Peshawar, Pakistan. The crystals are well developed and occur together with colorless and brown topaz. Gemological examination gave refractive indices of approximately 1.629–1.642, birefringence 0.009–0.011, and specific gravity 3.515–3.53. The stones show yellow, purple, and lilac-to-violet pleochroism and weak dark-red fluorescence under long-wave ultraviolet radiation. Chemical analysis showed small amounts of chromium and vanadium, with Cr³⁺ principally responsible for the pink coloration. Characteristic internal features include two-phase inclusions and parallel needle-like growth features. The article contains 17 color illustrations.

corundum, inclusions.5, photomicrography, gems

corundum, orange sapphire, Umba, Tanzania.12, inclusions.5, gems

As known to the gemmologist and jeweller, East Africa's famous gem locality, Tanzania, is well known not only for garnets of various colour varieties, but also for corundums of many colours and hues. The occurrence of corundum in Tanzania is reported by many researchers (Zwaan, 1974; Dolenc, 1976; Amstutz & Bank, 1977; Bank, 1978). However, these reports mainly describe the common corundum varieties such as ruby and blue and yellow sapphires. Recent observations made by the author on new occurrences of sapphires from Umba Valley revealed a reddish-brown colour variety which has often been termed as 'padparadschah* in the trade. It therefore became necessary to investigate systematically the differences between the 'real' padparadschah and this new occurrence. The chemical and physical properties of the latter are given with special emphasis on the cause of colour. Further, the inclusions are reported, which may be of help in documenting the locality.