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.

gems, jade, archaic jade, China, Chinese jade carving, nephrite, amphibole jade, cong, hsuen chi

For many years after its publication in 1912 Berthold Laufer's boo Jade : a study in Chinese archaeology and religion remained a standard referen work for Western scholars. In his third chapter Laufer discusses certain three-lobed jade discs (pl. I); he is in general agreement with the theories of the late-nineteenth-century Chinese scholar Wu Ta-ch'eng, who named the discs hsiian chi and suggested that they were origina intended to be used for astronomical purposes. After Laufer the discussion was taken up by other writers on jade, and was carried a stage further in series of papers by Henri Michel, beginning in 1947, in which he presented considerable amount of literary and scientific evidence in support of his interpretation of the astronomical purpose of the discs. Michel's theories were lent additional weight and given a wider circulation by their inclusion in Joseph Needham's survey of Chinese astronomy. Since Michel, those writers who have doubted the astronomical connexions of the discs have nevertheless tended to retain the name hsian chi, which now seems to have become established as the standard term for this particular jade form on museum labels and in archaeological reports in China as well as in the West.

corundum, Thailand.12, gems

The Tertiary Bo Phloi Basalt crops out in the area of approximately half a square kilometer, in the vicinity of Amphoe Bo Phloi, Kanchanaburi Province. It overlies quartzite of the Bo Phloi Formation of Silurian Devonian age. Generally, it is dark, dense, fme-grained and porphyritic. Megacrysts of clinopyroxene, black spinel and sanidine are commonly present. Ultramafic (spinel/peridotite/lherzolite) nodules or inclusions with varying size as well as xenoliths of gneissic rock, are frequently observed.

apatite cat’s eye, gems

Describes cat’s-eye apatite reportedly originating from the Umba Valley of northeastern Tanzania and identifies the inclusions responsible for its chatoyancy. Several kilograms of cuttable fragments offered in Nairobi as feldspar ranged from yellowish green and green to greenish brown and reddish brown. Although some fragments were transparent, most contained parallel fibrous inclusions that produced sharply defined cat’s-eyes when suitably fashioned as cabochons. The resulting stones were considered comparable in appearance and colour with fine chrysoberyl cat’s-eyes. Uniaxial optical behaviour excluded feldspar, and X-ray examination established apatite. Measured refractive indices range from 1.632–1.636 for the extraordinary ray and 1.636–1.640 for the ordinary ray, with a consistent birefringence of approximately 0.004. Dichroism separates yellowish and greenish, brownish and greenish, or reddish and brown components, and occasional colour zoning is observed. Sharp absorption lines between approximately 570 and 590 nm, attributed to the rare-earth elements praseodymium and neodymium, provide an additional diagnostic feature. Reported densities range from 3.22 to 3.35 g/cm³, with variation considered partly related to the inclusions. Microscopy shows fine reddish to blackish needles aligned parallel to the crystallographic c-axis. Their relatively coarse development, compared with fibres in previously known Brazilian and Indian cat’s-eye apatites, permits electron-microprobe investigation. Qualitative examination of fifteen needles detects iron, while quantitative analyses of a few sufficiently thick examples indicate a composition corresponding to FeOOH. The authors assign these needles to goethite rather than its polymorph lepidocrocite on the basis of their acicular habit. Larger irregular iron-rich masses occur among the fibres; one grain suitable for quantitative analysis is identified as hematite. Some specimens also contain reddish-brown discs composed of radially arranged goethite fibres. Their location almost exclusively within fissures indicates secondary formation, interpreted as evidence that iron remained available after the earlier inclusions had developed. The study attributes the cat’s-eye effect to light scattered by the parallel goethite fibres and demonstrates how conventional gemmological testing, microscopy and microprobe analysis together resolve both the identity of a mislabelled gem material and the mineralogical cause of its optical phenomenon.