beryl, emerald, Pakistan, gems, pegmatitic emerald, emerald geology

Emerald, formed by the substitution of a small amount of chromium for aluminum in the beryl crystal structure (Deer et al., 1986), results from rare geological conditions. While beryl—the most common beryllium-bearing mineral—is itself uncommon and primarily found in late-stage igneous rocks like pegmatites, emerald is even rarer due to the geochemical incompatibility between its two essential components: chromium and beryllium. Beryllium, with a small ionic radius (0.3 Å; Shannon and Prewitt, 1969) and a low crustal abundance (less than 5 ppm per Wedepohl, 1978; or less than 3.5 ppm according to Beus, 1965), is generally absent from the chromium-rich, ultramafic rocks where chromium resides in significant concentrations. Thus, emerald formation requires exceptional conditions that bring these two incompatible elements together, making emerald one of the rarest and most valuable gemstones. In Pakistan, a unique sequence of geological events created such conditions. The first three chapters of this book summarize these large-scale events, while chapters four through seven examine clues about emerald formation revealed through the physical and chemical characteristics of the crystals and the morphology and physicochemical formation conditions of their inclusions. Chapter 8 reviews the geology of other global emerald deposits. This cumulative analysis reveals a broader understanding of both Pakistani and global emerald genesis. The concluding chapter summarizes the characteristics of Pakistani emeralds and uses this data to formulate a theory of their origin, then proposes a classification scheme based on the geologic setting of global emerald deposits, developing it into a hypothesis for the genesis of all emeralds. Finally, suggestions for future research are offered to further elucidate emerald formation processes.

beryl, emerald, Pakistan, gems, pegmatitic emerald

Emerald is the exquisite result of the chemical substitution of a small amount of chromium (or vanadium) for aluminum in Be₃Al₂Si₆O₁₈, the mineral beryl (Deer and others, 1986). On the world gem market, if the green coloration of emerald is caused by any element other than chromium, it is not called emerald according to standards adopted by the London Chamber of Commerce and Industry’s Precious Stone Trade Section (Farm, 1975). The coexistence in nature of chromium and beryllium is unusual and thus emerald is one of the rarest and most precious gemstones. The general incompatibility of beryllium and chromium is the result of their different geochemical behavior as clearly demonstrated in the compilation of chemical data for igneous rocks by Wedepohl (1978). Beryl, the most common beryllium mineral, forms during late-stage (pneumatolytic and hydrothermal) igneous activity. Because Be²⁺ has a small ionic radius (approximately 0.3 Å; Shannon and Prewitt, 1969), it is excluded from the crystal structure of most minerals. In addition, because of the small average continental crustal abundance of beryllium (less than 5 ppm; Wedepohl, 1978), beryllium is not concentrated enough to form beryl until late stages of igneous activity, i.e., during the formation of pegmatites or hydrothermal deposits. In contrast, chromium, also a trace constituent in the Earth’s crust (averaging approximately 50 ppm; Wedepohl, 1978), precipitates early during igneous fractionation in the mineral chromite, FeCr₂O₄, or it substitutes for aluminum, iron, magnesium, or titanium in early igneous phases, such as pyroxene, amphibole, spinel, or garnet. Thus, the greatest abundance of chromium is found in ultramafic and mafic rocks. So even though chromium, which has an ionic radius of 0.62 Å (Cr³⁺; Shannon and Prewitt, 1969), will readily substitute for aluminum, which has an ionic radius of 0.54 Å (Al³⁺; Shannon and Prewitt, 1969), in the beryl crystal structure, chromium is not expected in the late-stage liquid or vapor from which beryl may be formed. Special circumstances are necessary to bring chromium and beryllium together; as a result, emerald is extremely rare and is found only where geologic processes have been favorable for its formation. One of the places on the Earth where the geologic environment is appropriate for emerald occurrence is the area of northern Pakistan and Afghanistan. In this region, oceanic and island arc rocks that are rich in chromium are juxtaposed against felsic, beryllium-bearing continental rocks of the Indian plate. Within this geologic setting, emeralds are found in two very different geologic environments. In the economically most important deposits, emeralds formed from hydrothermal fluids that penetrated along shear zones into talc-carbonate schists within mélange zones. In the other setting, the emeralds are in pegmatites or quartz-ankerite veins which intruded schist, gneiss, and amphibolite. In both cases, the beryl apparently precipitated from a late-stage beryllium-carrying hydrothermal or pneumatolytic fluid which had scavenged chromium from the host rock.

gems, beryl, emerald, Pakistan, Gujar Killi, Swat, Mingora

Over the last decade, Pakistan has developed into an important source for many gem materials. A number of localities have been identified for emeralds in particular. This article reports on the emerald deposits in the valley of Gujar Killi, located in the Northwest Frontier Province. The occurrence, mining, and gemological properties are described. Reserves appear to be good, and increased mining activity suggests strong production for the near future.

gems, beryl, emerald, Colombia, gold, shipwrecks, Florida Keys

During the 1970s and 1980s, treasure hunters discovered the centuries-old re-mains of the sunken Spanish galleons Nuestra Senora de Atocha and Santa Mar-garita. Not only did they find massive amounts of silver and gold in coins, bars, and chains, but they also uncovered a number of rough emeralds and several pieces of emerald-set jewelry. Recently, some of the treasures recovered from the Atocha were examined at the Santa Monica office of the GIA Gem Trade Lab-oratory. Gemological testing of the emer-alds revealed inclusions typical of stones mined in Colombia as well as possible ev-idence of extended submersion in s e w -ter. Study of the jewelry revealed a high-karat gold content and fine workmanship that represented methods typical of the era.

gems, jade, ruby, sapphire, spinel, beryl, emerald

A sumptuous catalog that accompanied shows in New York, Los Angeles and Toledo. Many aspects of the artistry and architectural skills that went into the creation of the world's most famous mausoleum are revealed. The buildings' depiction in artists' imaginations is also covered from many perspectives through the ages, by admirers from every culture. This article from the book focusses on Mughal jades.

corundum, History.1, gems, Indian lapidary

The fourth chapter of the Rasa Ratna Samuccaya, presented in Sanskrit with English translation and extensive explanatory notes by Damodar Joshi, is devoted principally to ratnas (gems) and is particularly important for the history of Indian gemology. Nine principal gems are associated with the nine planets: ruby, pearl, coral, emerald, topaz, diamond, sapphire, hessonite and cat’s-eye. The text describes desirable and defective qualities of gems and gives procedures for their śodhana (purification) and māraṇa (incineration) for medicinal use. Individual sections discuss ruby, sapphire, diamond, pearl and other gem materials, including their traditional physical characteristics, varieties, supposed planetary relationships, therapeutic properties and methods of processing. Additional materials treated include sunstone, moonstone, lapis lazuli and quartz (sphaṭika). Joshi’s notes compare the traditional descriptions with modern mineralogical identifications and chemical compositions. The chapter provides unusually detailed evidence for the intersection of gemology, medicine, astrology and alchemy in the Indian rasaśāstra tradition.

gems, ancient gemology, ancient jewelry, Egypt, Egyptian jewelry, beryl, emerald, turquoise, malachite, Islamic jewelry, Arabic mineralogy, rings, glyptic, engraved gems, gold

Hasson’s two-volume catalogue presents the Islamic jewellery collection of the L.A. Mayer Memorial Institute for Islamic Art, tracing the development of personal ornaments across the Islamic world from the early Islamic period into later centuries. The objects include rings, earrings, bracelets, necklaces, pendants, beads, amulets, belt and costume fittings, and related ornaments fashioned in gold, silver, and other materials and frequently set or decorated with gemstones, glass, and enamel. Individual entries describe materials, techniques, dimensions, decoration, inscriptions, provenance, dating, and comparable pieces, placing the jewellery within its archaeological and art-historical context. Particular attention is given to manufacturing and decorative techniques such as casting, repoussé, filigree, granulation, engraving, niello, openwork, and stone setting, as well as to recurring geometric, vegetal, figural, and epigraphic motifs. The catalogue illustrates both the continuity of jewellery forms across the Islamic world and regional differences resulting from interactions with Byzantine, Sasanian, Central Asian, Mediterranean, and other traditions. Together the volumes provide an important reference for the identification, dating, manufacture, and stylistic development of Islamic jewellery and for the study of gemstones and precious materials in Islamic decorative arts.

corundum, color.4, treatments.6, gems, color science

Studies concerning the origin of color in gem materials have grown in sophistication in recent years, so that much new in-formation is now available about natural color and its possible modification by var-ious treatment processes. This three-part series of articles reviews our current un-derstanding of gemstone coloration. The first part summarizes the factors that gov-ern the perception of color, from the source of light to the human eye, and then examines in detail the role of one color-cozising agent, dispersed metal ions, in the coloration of many gem materials, including ruby and emerald. The second part will explore charge-transferphenom-ena and color centers as the cause of color in gems such as blue sapphire and Maxixe beryl. The series will conclude with col-ors that can be explained usjng band theory and physical optics, such as the play-of-color in opal and the blue sheen of moonstone feldspars.

corundum, color.4, gems, color science

The fifteen causes of color derived from a variety of physical and chemical mechanisms are summarized in five Croups in this article. Vibrations and simple excitations explain the colors of incandescence (e.g., flames), gas excitations (neon tube, aurora), and vibrations and rotations (blue ice and water). Ligand-field-effect colors are seen in transition-metal compounds (turquoise, chrome-oxide green) and impurities (ruby, emerald). Molecular orbitals explain the colors of organic compounds (indigo, chlorophyll) and charge-transfer compounds (blue sapphire, lapis lazuli). Energy bands are involved in the colors of metals and alloys (gold, brass), of semiconductors (cadmium yellow, vermillion), doped semiconductors (blue and yellow diamond), and color centers (amethyst, topaz). Geometrical and physical optics are involved in the colors derived from dispersive refraction (rainbow, green flash), scattering(blue sky, blue eyes, red sunset), interference (soap bubbles, iridescent beetles), and diffraction (the corona aureole, opal).

corundum, sapphire, Cambodia.12, Thailand.12, ruby, Sri Lanka.12, Brazil, Mozambique, Zambia, Zimbabwe, South Africa, Namibia, opal, Mexico, Australia, emerald, gems

The first volume in CISGEM’s Gemmologia Europa series, bringing together contributions by leading European gemologists on important gem materials and gemological problems. The papers include discussions of diamond, emerald, opal and other colored stones, combining descriptions of deposits and geographic sources with gemological properties, inclusions, identification and aspects of formation. Among the contributors are E. Alan Jobbins, Henri-Jean Schubnel, Jan Kanis, Eduard J. Gübelin and Pieter C. Zwaan. Gübelin’s contribution, for example, compares Australian and Mexican opals. The volume provides a snapshot of European gemological research and expertise in the mid-1980s, with parallel English and Italian text. This includes Pailin sapphire, Sri Lankan gems, gems from Brazil, Mozambique, Zambia, Zimbabwe, South Africa, Namibia, and opal from Mexico and Australia.