corundum, properties.3, synthetic corundum.7, inclusions.5, gems

It has been generally accepted that asterism in corundum (star rubies and sapphires) is caused by needles of rutile (TiO₂) aligned along crystallographic planes of the corundum (e.g. Webster, 1962). The evidence given by Tait (1955) was: (1) the presence of titanium, (2) the needle-like habit, and (3) the square cross-section of the needles. Based on the analogy with rutilated quartz, and by eliminating octahedrite and brookite by the morphology, rutile was accordingly identified. This type of evidence, however, is explained equally well by either TiO₂ or the compound aluminum titanate Al₂TiO₆.

gems, jade, pyroxene jade, fei cui, jadeite, omphacite, kosmochlor, Guatemala, Costa Rica, Mexico, Maya, Olmec, Aztec, serpentine

In the central part of the San Augustin Acasaguastlan Quadrangle north of the Metagua River Valley, Guatemala, jadeite-rich rocks occur as inclusions in serpentine. The associated minerals are albite and in minor amounts, muscovite, actinolite and zoisite. The country rock is generally highly sheared serpentine, although massive serpentine is also present in lesser amounts. Most of the jadalte in the area is white or slightly greenish, having only small amounts of diopside, acmite and hedenbergite molecules. The green variety has a higher content of these pyroxene molecules and the variation in optical properties of the different specimens of jadeite analyzed is related to the impurities present. Jadeite seems to have formed before serpentinization of the ultrabasic body and later reacted with silica-bearing aqueous solutions forming secondary albite. Albitites are quite abundant in the area, occurring as large included bodies in the serpentine. From field relationship, chemical and mineral composition, they seem to have originated from a pegmatite which underwent desilication.

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

corundum, inclusions.5, gems

gems, garnet, red garnet, Dark Age garnet, Sweden

Mellis presents a nondestructive mineralogical investigation of 41 red stones from Merovingian- and Carolingian-period jewelry found in Sweden, undertaken both to establish whether the stones were actually garnets and, if possible, to determine their geographical origin. Because of the cultural and historical importance of the objects, the examination was restricted chiefly to refractive index, color and absorption spectra, specific gravity, anomalous birefringence, inclusions, and, for some specimens, single-crystal X-ray study. The small polished garnet plates are described individually, with detailed observations of their optical properties and inclusions, including various types of needles, prismatic and plate-like crystals, opaque minerals, zircon, and other phases. Chemical compositions were estimated from physical and optical properties and compared with established garnet compositional groups; the examined stones include pyrope-rich and almandine-rich varieties and mixtures of the principal garnet components. Mellis explores whether inclusions and composition can identify the geological environment and source of the stones, comparing the archaeological specimens particularly with garnets from Bohemia and other known occurrences. He concludes that inclusions alone cannot, at the existing state of knowledge, provide a reliable determination of geographical provenance, although inclusions combined with chemical composition can exclude certain geological environments and help characterize possible source rocks. The study demonstrates the value of detailed mineralogical examination of archaeological garnets while emphasizing the limitations of assigning ancient worked stones to specific deposits solely from their observable mineralogical properties.

gems, ancient gemology, ancient jewelry, Egypt, Egyptian jewelry

The majesty and splendor of ancient Egypt were largely due to the remarkably advanced technological skills developed by its artisans and craftsmen. This comprehensive and detailed study of ancient Egyptian technology meticulously documents how these workers, along with other Egyptians, exploited the land’s abundant resources. First published in 1926 and later revised and enlarged, this monumental work became a standard reference, unmatched in any other field of archaeology. The present volume reprints the fourth edition, thoroughly revised in light of more recent research and archaeological discoveries. Topics covered include a wide range of materials and techniques central to Egyptian life: the use of animal products, building materials, cosmetics, perfumes, incense, fibers, glazed ware, glass and its production, metals and alloys, painting materials, pottery, woodworking, precious and semi-precious stones, distillation of alcoholic beverages, and substances used in mummification. Profoundly erudite and rich in detail, Ancient Egyptian Materials and Industries is an indispensable reference for students of Egyptology and classical civilizations, and a vital resource for anyone interested in the long and remarkable history of technological innovation. Sinkankas: Drastically revised, rearranged: the substances now include beverages, animal products, building materials, cosmetics, perfumes & incense, ceramics & glass, fibers, metals & alloys, mummification materials, oils, fats, waxes, painting materials, pottery & its manufacture, gemstones, other stones, woods & woodworking, and a historical analysis. Ch 12, [335–54], on gemstones, among which now additionally appear coral, amber, malachite, and jade, while horn, ivory, nacre and tortoiseshell are described in Ch 2. Ornamental stones are treated in Ch 13, [355–75]. The author notes that “diamond, opal, ruby and sapphire were not known to the ancient Egyptians.” In his preface, Harris notes the inclusion of information taken from recent studies, with references added to the list in the previous edition. Much technological information is also added, with an appendix of reliable chemical analyses. “The most consistent modification has, however, been in matters of lexicography, in order to eliminate invalid evidence derived from inaccurate or disputed translations of Egyptian texts.” In this connection, see also Harris’ Lexicographical Studies in Ancient Egyptian Materials, 1961. In this edition, the following places are of gemological interest: beads, Ch 4, [41–7] (includes gemstone materials); inlaid gemstone eyes, Ch 7, [98–127] (many types & examples); gemstones in general, Ch 16, [386–405]; other stones, Ch 17, [406–28]. Lucas should always be consulted whenever one writes or lectures about Egyptian jewelry.

corundum, ruby, sapphire, Tanzania.12, East Africa.12, inclusions.5, gems

gems, corundum, properties.3, synthetic corundum.7, spinel, chrysoberyl, quartz, tourmaline, zircon, scapolite, spinel inclusions

inclusions, microscopy, gems

corundum, ruby, sapphire, synthetic corundum.7, synthetic ruby, synthetic sapphire, gems

Chudoba and Gübelin provide a practical guide to distinguishing natural gemstones from synthetic counterparts, combining a short history of artificial gem production with detailed discussion of the principal manufacturing methods and their diagnostic consequences. The Verneuil flame-fusion process, flux growth, and hydrothermal synthesis are described, together with the characteristic structures and inclusions they produce. Particular attention is given to synthetic ruby and sapphire, spinel, emerald, and other important gem materials, with comparisons between natural and laboratory-grown stones based on growth zoning, curved striae, gas bubbles, mineral inclusions, refractive properties, fluorescence, and other microscopic and physical features. The authors emphasize examination with the gemological microscope as one of the most powerful means of separation, supported by numerous photomicrographs illustrating inclusions and growth phenomena in both natural and synthetic gems. Conceived as a concise working manual for gemologists and jewelers, the book brought together the principal identification criteria then available at a time when synthetic gemstones were becoming increasingly sophisticated and commercially important.