corundum, inclusions.5, gems

corundum, ruby, sapphire, inclusions.5, parting, physical properties.3, gems

The pronouncedparting observedin much corundumhastraditionally beenattributedto twinning. This studyidentiflesboehmiteasoccurringin seamsalongthe {IOTU Partingdi-rections.Corundum'sparting is, therefore,due to the weaknessof the boehmite-corundum contact.The boehmiteis believedto be a product of exsolution.

corundum, Cambodia.12, Pailin, blue sapphire, ruby, inclusions.5, geology.11, gems

The most detailed report ever prepared on the ruby and sapphire fields at Pailin, Cambodia.

inclusions, gems

Sinkankas: This physically large and elegantly designed book features handsome illustrations and reflects the considerable effort invested by the editors in locating notable gems and jewels—such as the Wittelsbach diamond—in order to produce new photographs. Many of the pieces included had never before been available for photography, and those previously published now appear in superior new images. The book originated from this remarkable photographic assemblage and was expanded with essays that align with its central theme. Of particular gemological interest is Eduard Gübelin’s opening essay, “The Origin of Gemstones” (pp. 15–32), which, though not focused on geological genesis, provides a general survey accompanied by photos of rough and cut gems. Billeter explores the timeless allure of gems in personal adornment, Gregorietti examines ancient precious ornaments, while Higgins and Tait of the British Museum trace the evolution of jewelry styles and forms. Other contributors include Ledit, who discusses sacred jewels as artistic objects; Lightbown, who covers regalia and ceremonial items; Neu, who addresses modern jewelry; and Switzer of the Smithsonian Institution, who describes some of the world’s most famous gems. The volume also includes a summary table detailing gemstone properties, sources, and historical periods of peak use. As expected from a high-quality “coffee-table” book, the illustrations are exceptional, though the generous type size and limited space for contributors mean the essays offer only cursory overviews of their respective subjects.

corundum, ruby, sapphire, inclusions.5, treatments.6, Australia.12, Burma.12, India.12, Kashmir.12, Sri Lanka.12, Tanzania.12, Thailand.12, Cambodia.12, USA.12, Montana.12, gems

Sinkankas: Lavishly produced and handsome, this work is a successor to the author’s previous book on inclusions (1953), but differs in several notable respects, mainly through its exclusive use of color photographs and through considerable elaboration of the text on the genesis of inclusions. The introduction by Wilhelm Friedrich Eppler provides a brief history of the investigation of inclusions in crystals and describes the ways by which they can be examined and identified, including the use of the electron microprobe. Gübelin explains genetic types of inclusions and the categories to which they are assigned, then passes to descriptions of inclusions typical of diamond, corundum, beryl, feldspar, garnet, peridot, quartz, spinel, topaz, tourmaline, and zircon, with the final section of text describing characteristic inclusions in a number of synthetic materials. The glossary defines technical terms and gives brief descriptions of inclusion species mentioned in the text. The bibliography, unfortunately without pagination, covers the important contributions to the study of inclusions and is not confined to gemstones but considers other minerals as well. The photographs, of superb color quality and sharpness of detail, are expected to provide ready visual reference as the student examines inclusions under the microscope. The lamentable use of cement-backed binding for so important a work is disastrous; leaves already spring loose from the first opening of the book. Regarding the problem of finding illustrations useful to a current project, Karl Zigerli indexed the work so that readers could quickly find crystals of the species and varieties, and the inclusions desired, among the many illustrations; this index appeared in Zeitschrift der Deutschen Gemmologischen Gesellschaft, 25(4), 1976, pp. 222–225. Review: Zeitschrift der Deutschen Gemmologischen Gesellschaft, 25, 1975, pp. 51–52.

gems, corundum, inclusions.5

Recently, a paper was published describing inclusions of corundum within corundum. The stones in question are light blue sapphires with a tinge of green, or alternatively brownish or purple-colored corundums. They are found in the Umba mine near the Umba River in northeastern Tanzania, close to Mount Kilimanjaro. The inclusions are elongated needles that, at first glance, resemble the well-known rutile needles often seen in corundum. Figure 1 illustrates that the needles follow three directions that appear to be at right angles to one another. Figure 2 reinforces this impression; however, in reality, the angles differ slightly but measurably from 90°. According to the cited publication, these needles run at right angles to the faces (42̅1), (22̅1), and (24̅1), which are steep hexagonal pyramid faces. X-ray analysis revealed that the needles are composed of corundum and occur in “twin positions” relative to the host crystal. Surprisingly, each of these needles is themselves twinned parallel to the prism faces of the surrounding corundum. Furthermore, the needles are of secondary origin, having formed after the host crystal. This, along with the fact that the inclusions induce considerable internal stress, suggests that the needles may have formed due to pressure. However, this theory has not yet been conclusively proven.

corundum, ruby, Thailand.12, Cambodia.12, inclusions.5, gems

corundum, Burma.12, Sri Lanka.12, Thailand.12, gems

Sinkankas: In this pictorial popular work, the author provides a nontechnical description of the major gemstones in a language that stresses the beauty and fascination of gems and deliberately suppresses dry scientific data. Thus the book begins with several chapters extolling the wonders of gemstones, their colors and origins, the special beauty of gems that display color or reflective phenomena, inclusions in such gems as moss agates, and a little on the splendid crystals from which gems are cut and their sources in nature. Other chapters touch on the arts of the lapidary, the diamond, the corundum family, and many other gemstones, ending with a chapter on the Idar-Oberstein agate-cutting and carving industry, and closing with a very brief chapter on the true value of gemstones in their aesthetic appeal. The book includes a glossary in which technical terms are defined and the basic properties of gemstones mentioned elsewhere are summarized. There is no index nor bibliography. The most striking feature is the large number of superb color photographs, ranging from faceted gems, some obviously selected from the finest available for illustration, to cabochons, carvings, natural crystals, views of lapidary work in progress, scenes in famous gem-mining areas, jewelry, and objects of art made from stone. These are of particular value and reflect the author’s wide travels. Not seen. Reviews: Zeitschrift der Deutschen Gemmologischen Gesellschaft, 18(4), 1969, pp. 193–194; Der Aufschluss, 21(12), 1970, p. 384.

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

Sinkankas: Aside from Iyer & Thiagarajan’s Indian Precious Stones (1961), which see, almost all information on the gemstones and gem industry of Ceylon had appeared in short articles scattered throughout a large variety of journals, both technical and nontechnical. Thus the present authoritative work clearly supersedes all previously published information and is based on the author’s numerous visits to the island. It is filled with splendid photographs, both scenic and pertaining to the industry. The text gives a sketch of the island’s geology as well as details of the alluvial deposits that furnish practically all of the gem material. Historical notes support the thesis that these gem deposits supplied gemstones to much of Asia, Egypt, and Europe from time immemorial. The section treating mining is exceptionally detailed and beautifully illustrated, discussing all the factors that must be taken into consideration before the commencement of mining operations and the traditional rules by which such activity is governed. Equally thorough are descriptions of the unique lapidary work and of the progress of the rough stone from mine to finished gem and ultimate sale. Descriptions of individual gemstones cover qualities, relative rarity, specific sources, properties, and diagnostic inclusions. Properties and absorption-spectra data are summarized in tabular form in the last part of the work. There is also a less detailed section on organic gem materials which furnishes an up-to-date account of the pearl fishery and contains remarks on coral and tortoiseshell. This work apparently was published at the author’s expense, although it is understood that copies were also made available through Rühle-Diebener Verlag, Stuttgart, at DM 38. Reviews: Der Aufschluss, 21(12), 1970, p. 384 (price given as DM 25.74); Journal of Gemmology, 11(6), 1969, p. 220 (price given as 70s); National Geographic, 64(1), 1969, pp. 74–75.

gems, corundum, ruby, sapphire, inclusions.5