corundum, synthetic corundum.7, gems

Gemological investigations of Tairus hydrothermal synthetic ruby revealed characteristic microscopic features, including solid alloy inclusions consisting mainly of copper–iron alloys and wavy growth lines. Chemical analysis by microprobe showed that the chromium concentration in the area of the growth lines averaged 3.81 wt.% Cr₂O₃, as compared to 1.53 wt.% Cr₂O₃ in the remainder of the stone. Characteristic infrared absorption peaks are 3308, 3233, and 3186 cm⁻¹.

gems, beryl, aquamarine, morganite, inclusions, Pakistan

Emerald mineralization is found within 0.1- to 1-m-thick hydrothermal veins and granitic pegmatites cutting amphibolite within the Nanga Parbat-Haramosh massif, in northern Pakistan. The amphibolite forms a sill-like body within garnet-mica schist, and both are part of a regional layered gneiss unit of Proterozoic (?) age. The 40 Ar/ 39 Ar data for muscovite from a pegmatite yield a plateau age of 9.13+ or -0.04 Ma. Muscovite from mica schist and hornblende from amphibolite yield disturbed spectra with interpreted ages of 9 to 10 Ma and more than 225 Ma, respectively, which indicate that peak Tertiary metamorphism reached 325 to 550 degrees C prior to 10 Ma. Pegmatites were emplaced after peak metamorphism during this interval and are older than pegmatites farther south in the massif. At Khaltaro, simply zoned albite-rich miarolitic pegmatites and hydrothermal veins containing various proportions of quartz, albite, tourmaline, muscovite, and beryl are associated with a 1- to 3-m-thick heterogeneous leucogranite sill, that is locally albitized. The pegmatites likely crystallized at 650 to 600 degrees C at pressures of less than 2 kbar. Crystals of emerald form within thin (<30 cm) veins of quartz and tourmaline-albite, and more rarely in pegmatite, near the contacts with altered amphibolite. The emerald-green coloration is produced by Cr and Fe. The Cr and total Fe contents, expressed as Cr 2 O 3 , and Fe 2 O 3 , respectively, decrease systematically from emerald (>0.20, 0.54-0.89 wt%), to pale blue beryl (< or =0.07, 0.10-0.63%), to colorless beryl (<0.07, 0.07-0.28%). The amphibolite is metasomatized in less than 20-cm-wide selvages that are symmetrically zoned around veins or pegmatites. A sporadic inner zone containing F-rich biotite, tourmaline, and fluorite, with local albite, muscovite, quartz, and rare beryl, gives way to an intermediate zone containing biotite and fluorite with local plagioclase and quartz, and to an outer zone of amphibolite containing sparse biotite and local quartz. The inner and intermediate zones experienced gains of K, H, F, B, Li, Rb, Cs, Be, Ta, Nb, As, Y and Sr, and losses of Si, Mg, Ca, Fe, Cr, V and Sc. The outer alteration zone has gained F, Li, Rb, Cs, and As. Oxygen isotope analyses of igneous and hydrothermal minerals indicate that a single fluid of magmatic origin with delta 18 OH 2 O = 8 per mil produced the pegmatite-vein system and hydrothermal alteration at temperatures between 550 and 400 degrees C. The formation of emerald result from introduction of HF-rich magmatic-hydrothermal fluids into the amphibolite, which caused hydrogen ion metasomatism and released Cr and Fe into the pegmatite-vein system.

gems, ancient gemology, ancient jewelry, early metallurgy, collection, comparanda, catalog

On the occasion of the 50th anniversary of the Würth Group in 1995, a unique exhibition on the history of the screw and the thread in antiquity was presented for the first time through a joint effort by the Museum Würth in Künzelsau-Gaisbach and the Archaeological State Museum of Baden-Württemberg. The exhibition was supported by over twenty museums in Europe and the USA with precious Late Antique jewelry exhibits. Special thanks are due to co-initiator Dr. Rüdiger Krause, director of the Archaeological State Museum and president of the State Heritage Office of Baden-Württemberg, to Prof. Dr. Dieter Planck, and especially to Reinhold Würth and all the scholars involved in the research project, for making this exhibition possible, which has now been crowned with a scholarly publication on a topic previously neglected in general cultural history. The exhibition’s preparation and the development of the volume were preceded by intensive and thorough research on the topic of threads in antiquity. This involved not only ancient threading techniques based on archaeological remains or written sources attesting to such techniques, but also the political and social conditions of Late Antiquity, which were particularly defined by rank insignia and prestige objects (fibulae, arm rings, bracelets, pectorals, pectoral crosses, belts, etc.) using screw fastenings. The richly illustrated and high-quality volume, featuring numerous (including full-page) color and black-and-white images, drawings, and maps, is structured as follows: after the introductory foreword by Reinhold Würth (pp. 7–13) and the exhibition introduction by Dieter Planck (pp. 14–22), the main thematic section is divided into four specific areas: Rüdiger Krause writes on “The Thread in Antiquity” (pp. 23–54), Astrid Schürmann on “The Transmission of Ancient Authors” (pp. 55–76), Barbara Theune-Großkopf on “Onion-Head Fibulae and Their Wearers – Jewelry and Rank Insignia” (pp. 77–112), and Barbara Deppert-Lippitz on “The Golden Jewelry of Late Antiquity” (pp. 113–140). A special feature of the volume is the inclusion of English and French summaries preceding each article, along with trilingual captions (German, English, French) for all images.

corundum, synthetic corundum.7, gems

, gems

synthetic corundum.7, ruby, sapphire, synthetic spinel, flame fusion, Verneuil, gems

Describes the Verneuil flame-fusion process and the diagnostic features used to identify gemstones produced by it. Particular attention is given to microscopic inclusions and absorption spectra, with illustrations showing characteristic features of flame-fusion synthetics. The article explains how evidence resulting from the growth process can distinguish these laboratory-grown materials from their natural counterparts and provides practical criteria for routine gemological identification. A contemporary Journal of Gemmology abstract specifically confirms this emphasis on the Verneuil process, inclusions and absorption spectra.

gems, inclusions, beryl, emerald, Madagascar

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

gems, beryl, emerald, inclusions, Brazil

quartz, inclusions, gems