gems, ancient gems, glyptic, archaeology, archaeogemology, Ethiopia, Red Sea, Eritrea, olivine basalts, geology, analytical

The island of Kod Ali is a small diatreme cone lying close to the Ethiopian coast at latitude 13° 57′ N, longitude 41° 49′ E. This volcanic structure, produced by geologically Recent volcanic activity, consists, almost entirely, of pyroclastic debris. Evidence of a liquid phase is confined to the thin veneers of markedly alkalic olivine basalt which coat many of the abundant gabbroic, pyroxenitic and lherzolitic fragments found on the island. As silicic inclusions are completely absent and as the alkalic liquid phase and the “tholeiitic” inclusions are seemingly genetically unrelated, it is proposed that the latter might have been derived from a tholeiitic plutonic layered sequence that underlies the tholeiitic basalts of an “oceanic” Red Sea floor.

corundum, India.12, ruby, sapphire, history.1, gems, Indian lapidary

Sinkankas: Gemstones as viewed by an Indian author steeped in traditional lore presents a perspective deeply rooted in India’s enduring cultural relationship with gems, much of which remains seriously regarded today. As noted in a review in Gems & Gemology (Vol. 14, No. 2, 1972, pp. 61–63), the work is a unique combination of Indian culture and gemology." The lengthy and valuable introduction offers insights into Indian gem lore, tracing its origins to ancient texts as well as to more recent sources, many of which are cited by the author, Tank, along with the names of their authors. Topics discussed include the critical importance of imperfections in gems, distinctions between synthetics and naturals, and traditional Indian classifications, listing 84 gemstones in total. At the heart of the book is a focus on the nine traditional gems—emerald, diamond, pearl, coral, zircon, blue sapphire, sapphire, ruby, and cat’s-eye—shown on the color plate preceding the text. These are described using both traditional beliefs and modern scientific knowledge, with an emphasis on the qualities a gem must possess to be considered protective or influential. Tank also explores various gem varieties, their sources, and recommendations for when and where they should be worn for their protective powers. For instance, in the case of pearls, shape is crucial, and over 20 forms are illustrated with their Indian names. The book also includes synonyms for gems in different Indian languages and covers additional stones such as garnet, feldspar, quartz, opal, topaz, tourmaline, and beryl. It concludes with short notes on lapidary treatments and birthstones. Monochrome plates primarily depict cutting styles and one plate on inclusions. Unfortunately, and typically of much modern bookbinding in India, the physical binding is very poor—the spine is unrounded and the inner hinges tend to break upon opening. As noted in Rev/Gemm (Vol. 13, No. 6, 1973, p. 239), the book is not a scientific treatise."

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

Sinkankas: Typically written in simple, clear language and compiling articles originally published in Lapidary Journal, Oct. 1964–July 1968, with revisions. First 15 chapters on nomenclature, properties, crystallography, optical phenomena, color, inclusions, synthetics & imitations, testing procedures and instruments used, after which appear the remaining chapters on descriptions of gemstones, with organic materials treated in the last two chapters. The strong interest of the author in inclusions is apparent with much text devoted to same and hundreds of inclusion photographs; these form a most valuable part of the work. Rev. G & G, 13, 3, 1969, 103. Reprinted several times commencing in 1970.

corundum, synthetic corundum.7, Kashan, gems

Describes the Kashan synthetic rubies produced by the flux-growth process and examines the features by which they may be distinguished from natural ruby. The material shows the color and general appearance of fine natural ruby, making recognition potentially difficult without careful examination. Particular attention is given to characteristic internal features associated with flux growth, including residual flux and distinctive growth structures, and to their value in separating the synthetic stones from natural corundum. The article emphasizes the gemological importance of recognizing these diagnostic inclusions as flux-grown synthetic rubies became commercially available. One of the first references to Kashan synthetic rubies

gems, beryl, emerald, Brazil, Colombia, China, Zimbabwe, Pakistan, Zambia, Madagascar, Mozambique, inclusions

Sinkankas: Very handsome, imaginatively designed book, with the unusual feature of the title being spread over three pages. Apparently this work was meant to be the first of a series of monographs on gemstone families but up to date (1988) no others have appeared. The first part treats emerald history, in the East, as known to Pliny, origin of the name, curious lore surrounding, famous emeralds, and the color and causes. The second part describes world emerald deposits with most space naturally devoted to the Colombian mines, type crystals, and a discussion of trapiche crystals. The third part provides property data, considerable detail on inclusions in emerald, doublets & imitations, and the methods of gemological investigation . Next appear four tables of constants of natural & synthetic emeralds, comparisons of emerald to other similarly-colored stones or imitations, and fluorescence of emeralds from various deposits. The bibliography, unfortunately, is replete with errors in contrast to the text which is relatively free of defects. The mostly high quality illustrations show natural specimens, minerals that could be mistaken for emerald, cut stones, a Russian postage stamp depicting Siberian emerald, jewelry set with emeralds, absorption spectra, and many photographs of inclusions but these last lack the quality of the other illustrations. Rev R K Mitchell, J Gemm, 11, 7, 1969, 272–3, notes errors in biblio & elsewhere.

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.