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

Bank surveys the principal gemstones then known from Tanzania and relates them to their geological occurrences and mineralogical properties. Following an outline of Tanzanian geology, he treats diamond, garnet, corundum, zoisite, prase opal, diopside, and chromium-bearing tourmaline. Garnets include pyrope–almandine “rhodolite,” hessonite, yellow-green and colorless grossular, and rare emerald-green Cr-bearing grossular from the Mirarani Hills. Corundum is described from the Longido zoisite-amphibolite, where large ruby porphyroblasts show pronounced zoning, parting, rutile needles, and other inclusions; additional Tanzanian deposits yield ruby, sapphire, padparadscha, and fancy-colored corundum. Particular attention is given to transparent blue zoisite from the Mirarani Hills, discovered in 1967, including its pleochroism, optical properties, trace elements, heat-induced color modification, color change, and occasional chatoyancy; its occurrence is described in pegmatitic-hydrothermal veins or fracture fillings with quartz, feldspar, grossular, and diopside. The paper also records nickel-colored green prase opal from Hanety Hill, yellowish-green gem diopside, and emerald-green Cr-tourmaline from the Lelatema Hills, providing refractive indices, densities, lattice constants, trace-element data, and other mineralogical properties for many of the materials.

corundum, synthetic corundum.7, gems

Webster surveys synthetic crystalline materials developed since 1946 that have entered the gemstone trade or offer potential for ornamental use, bringing together scattered literature and results from his own examinations. Arranged alphabetically by chemical or species name, the review includes synthetic equivalents of natural minerals and manufactured compounds without known natural counterparts. Established pre-war Verneuil corundum and spinel receive only limited attention, while crystal-growth methods are outlined rather than discussed in detail. Identification is approached through physical and optical constants, internal features, absorption spectra, fluorescence and phosphorescence, X-ray transparency, electrical conductivity and, where relevant, magnetism. Particular attention is given to synthetic emeralds from Chatham, Gilson, Zerfass and Linde, together with Lechleitner’s synthetic-emerald-coated beryl and layered constructions. Earlier synthetic emeralds commonly differed from natural stones in refractive indices, birefringence and density and showed characteristic veil-like inclusions and strong luminescence. More recent products increasingly overlap natural emeralds in their measurable properties; the addition of iron can suppress luminescence, making careful examination of inclusions especially important. Flux-grown and hydrothermal rubies likewise present greater identification difficulties than conventional flame-fusion material, with seed remnants, feathers, distinctive inclusion patterns and radiation responses providing possible evidence of synthesis. The diamond section records the progression from commercially useful industrial crystals to General Electric’s May 1970 announcement of gem-quality synthetic diamonds of approximately one carat or more, while noting that production costs still exceeded those of comparable mined stones. Extensive coverage is also given to garnet-structured compounds, particularly yttrium aluminium garnet, and to diamond simulants including strontium titanate, rutile and lithium niobate. Their usefulness and detection are considered in relation to dispersion, birefringence, density, hardness, colour and durability. Other entries discuss coloured synthetic quartz, fluorite, scheelite, periclase, silicon carbide, zincite, zircon and several less familiar or experimental materials. Developments in spinel include red flame-fusion stones, flux-grown crystal groups used uncut in jewellery, sintered material imitating lapis lazuli and material displaying a moonstone effect. Throughout, trace-element additions are shown to influence colour, spectra and luminescence, so that specimens of the same nominal material may behave differently. Photomicrographs, spectral diagrams, a comparative radiograph, tables of constants and a selected bibliography support the descriptions. The compilation distinguishes established commercial products from experimental or merely prospective gemstones and provides a contemporary reference for the increasingly varied identification problems posed by synthetic crystals.

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, quality.10, fashioning.9, cutting, gems

Sinkankas provides a comprehensive reference catalogue of gemstones intended for gemologists, jewelers, collectors, and mineral enthusiasts. The entries are arranged systematically and describe natural gem materials in terms of their mineralogical and gemological properties, including chemical composition, crystal system, hardness, specific gravity, refractive indices, optical character, color, cleavage, inclusions, and other diagnostic features. Discussions also cover important localities, occurrence, varieties, nomenclature, cutting and use, and methods of identification, with attention to materials that may be confused with one another. Synthetic stones, imitations, and less familiar ornamental materials are also considered where relevant. Designed for practical consultation rather than continuous reading, the volume brings together a large body of mineralogical and gemological data in a compact reference work for identifying and studying gem materials.

gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology, Sahagun, codices, codex, serpentine

An Olmec figurine said to have been found at La Venta falls stylistically within the range of variation of other figurines known to be from that site. Four designs engraved on the upper parts of the limbs represent abstract were-jaguar heads identical with those of the serpentine mosaic pavements at La Venta. Thus, the pavements should be considered examples of the Olmec style and not, as has been claimed, pre-Olmec. In 1965 an important Olmec figurine (Figs. 1 and 2) was acquired by the Robert Woods Bliss Collection of Pre-Columbian Art at Dumbarton Oaks, Washington, D.C. The provenience is not definitely known, but it is said to have been found at La Venta in the state of Tabasco, Mexico. The material from which the piece was carved is a white to greyish-buff serpentine with small, shiny black inclusions. While presently 8.1 cm in height, the figurine had been broken in ancient times, so that one foot is missing, as well as the lower part of the other leg. There has been no restoration, although a recent break across the left shoulder and the chin has been repaired. The material, workmanship, and patination all testify to its authenticity.

gems, jade, pyroxene jade, jadeite, fei cui, omphacite, kosmochlor, Guatemala, geology

Jadeite occurs as inclusions in serpentinite in the Motagua fault zone. A boulder of remarkable size and purity was found near Manzanal, Guatemala, and chemical, optical, and X-ray studies have been made of a separated sample of the jadeite. Elsewhere in the Motagua fault zone, omphacite-garnet eclogites and glaucophane-lawsonite-omphacite-garnet rocks have been found in similar environments. Only at the Manzanal locality, however, have sodic pyroxenes been found in rocks which are nearly monomineralic.

corundum, ruby, sapphire, inclusions.5, Kashmir.12, India.12, gems

Schubnel examines the identification of solid inclusions in gemstones through laboratory techniques that supplement microscopic observation, emphasising their value in establishing natural origin and, in some cases, suggesting a probable geographical source. Reporting results obtained during the preceding two years, he explains that inclusions around one tenth of a millimetre or smaller need no longer present insurmountable identification problems when suitable mineralogical equipment is available. The choice of method must nevertheless be adapted to the individual stone, and the general inability to subject cut gemstones to destructive testing imposes practical restrictions. Direct determination is confined to inclusions that reach the surface; in rough crystals, polishing a face may be necessary to expose the inclusion. Three complementary approaches receive particular attention. Chemical analysis with the Castaing electron microprobe uses characteristic X-ray emission to establish the composition of very small inclusions. Microscopy in polarised reflected light provides optical observations and measurements, particularly for opaque minerals. X-ray powder diffraction can identify crystalline material removed from inclusions in rough stones, while measurements with a Leitz microhardness instrument leave square impressions only a few micrometres across. Illustrated identifications include pyrrhotite and chlorapatite in a mauve sapphire, a spinel containing 3% zinc in a cut ruby, and calcite in ruby. A more detailed example, presented in French, English and German as a suggested format for communication among inclusion specialists, describes calcite inclusions in a faceted ruby of presumed Burmese origin. Examination in transmitted light with the ruby immersed in methylene iodide reveals a large inclusion whose faces resemble a nail head and whose cleavage planes are clearly visible. Because this inclusion reaches the surface, its identification could be investigated using the Castaing microprobe, reflected-light microscopy and microhardness testing. The article anticipates increasing difficulty in distinguishing natural from synthetic gemstones and proposes systematic investigation of inclusions, particularly through microprobe analysis, as a means of improving the confidence with which gemmologists and mineralogists recognise and distinguish inclusion types.