jade, jadeite, fei cui, nephrite, Wyoming, Burma, inlusions, gems

ekanite, gems

Gübelin gives a detailed gemological account of ekanite, a newly recognized metamict gem mineral from Ceylon, named for F. L. D. Ekanayake, who first recognized its unusual character. The material occurs in the gem gravels near Ellawala, northeast of Ratnapura, and is typically greenish-brown to yellowish-green, transparent to translucent, and sometimes displays chatoyancy or asterism caused by oriented clouds of minute inclusions. Gübelin describes its gemological properties, including its singly refractive character, refractive index of about 1.595, specific gravity of about 3.28, and weak absorption bands, together with microscopic features and inclusions. Chemical investigation showed calcium, thorium, silicon, aluminium, and lead, while measurements demonstrated significant radioactivity associated particularly with thorium. The destruction of the original crystal lattice through radioactive decay accounts for its metamict condition. Gübelin also discusses its probable original crystalline state, chemical composition, and age as estimated by thorium-lead dating, establishing ekanite as an unusual new addition to the gem minerals of Ceylon.

corundum, synthetic corundum.7, gems

Describes ruby specimens consisting largely of natural cores covered by thin synthetic layers, reportedly grown hydrothermally. Their physical constants match natural ruby, and inclusions within the cores can make identification misleading. Minute gas bubbles in the coating and a sharp boundary between core and overgrowth reveal their composite nature; the observed features suggest growth from a melt rather than a hydrothermal process.

corundum, Brazil.12, gems

Describes sapphire crystals from the Coxim River area of Mato Grosso, Brazil, noting unusual rounded inclusions resembling the gas bubbles commonly associated with synthetic corundum.

phase-contrast microscopy, gems

Explains the application of Zernike’s phase contrast microscopy to reveal subtle internal features in gemstones. By converting differences in optical path into visible brightness contrasts, the method enhances thin, transparent inclusions and structures whose refractive indices closely resemble those of their hosts. Specially adapted equipment permits examination within gemstones, revealing exsolution, alteration and healed fractures that are difficult to distinguish under ordinary illumination.

corundum, USA.12, Idaho.12, gems

A corundum occurrence examined in August 1950 in Valley County, Idaho, approximately five miles east of Smiths Ferry, provides an example of the mineral preserved in its original rock matrix and a possible model for the source of corundum recovered from Idaho gold placers. Earlier reports recorded corundum and sapphires from numerous placer localities, including tributaries of the Payette River, creeks near Pierce, the Stanley Basin, Salmon River gravels and the Burgdorf district, but their source rocks had generally remained unidentified. A historical account from Rock Flat near Meadows suggested derivation from a weathered basaltic dike, although this interpretation had not established an unequivocal occurrence in original matrix. At the newly described locality, corundum occurs as metacrysts within schist inclusions enclosed by granodiorite of the Idaho batholith. The largest inclusion observed measured approximately thirty feet across, and the limited dimensions were considered to preclude commercial development. The corundum-bearing schist consists principally of dark olive-green biotite, oligoclase of approximately An11 composition and corundum, the latter constituting an estimated 15–20% of the rock. Corundum crystals reach three centimetres in length and two centimetres in diameter, although crystals only one to two millimetres long are also common. Biotite grains average two to three millimetres across, while the much finer feldspar averages approximately 0.1 millimetres and tends to concentrate around the corundum. Minor associated minerals include an unidentified amphibole, chlorite, muscovite, magnetite and martite; muscovite, magnetite and martite also occur as inclusions within corundum. Well-formed corundum crystals are absent: many grains are irregular, some are nearly tabular, and most display a linear orientation within the schist’s foliation plane. Whole crystals range from light grey to buff, whereas crushed fragments are predominantly clear, with subordinate very pale blue, lavender and pink material. Selected material yielded a pycnometer specific gravity of 3.91. Refractive indices were not accurately determined, but identification was confirmed by an X-ray pattern. Although the locality itself was not regarded as a potential commercial source, the occurrence suggests that comparable metamorphic rocks could supply placer corundum. Examination of the narrow metamorphic belt bordering the Idaho batholith approximately twelve miles farther west is therefore proposed as a worthwhile direction for further investigation.

corundum, Sri Lanka.12, gems

Sinkankas: Describes the rock groups, mineral occurrences, typical deposits, rocks of secondary origin, fossils, and recent sedimentary rocks of Ceylon, together with gems and gem mining, a list of gemstones, and the arrangement of the mineral gallery at the Colombo Museum. Not seen; some sources identify the original publication as Spolia Zeylanica, Vol. 3, Part 9, March 1905, pp. 50–66, and also record its inclusion in the Colombo Museum’s Guide to the Collections (1905).

gems, early lapidaries, Marbode, Middle Ages, Medieval

Sinkankas: Generally regarded as the most authoritative and useful edition, due to the notes on previous editions and the citations of several versions of the poem. Schuh: Marbode, whose true name was de Marboeuf," received his early education at Angers. After teaching some time at the cathedral school of Angers, he was put at the head of the educational system of the city and Diocese of Anvers in 1067. Later he became archdeacon and in 1096 Urban II appointed him Bishop of Rennes. In his youth he indulged in many excesses, but from the time he became bishop his life was without reproach. In 1104 he was present at the Council of Tours, and in 1109 he was made administrator of the Diocese of Angers. At the age of eighty-eight he resigned his diocese and withdrew to the Benedictine monastery of St. Aubin at Angers where he died soon after. Of the 1799 edition, Schuh said: Scarce. Edited by Johann Beckmann. Regarded as the most authoritative and useful early edition because of the inclusion of notes and citations from previous editions, including those of Pictorius and Alaard."

corundum, treatments.6, inclusions.5, gems

Nice video lecture of gemologist John Koivula lecturing on gem treatments.