gems, Afghanistan, Panjshir Valley, beryl, emerald, iron, silver

This chapter summarizes and interprets results from joint geologic and compilation activities conducted during 2009 to 2011 by the U.S. Geological Survey, the U.S. Department of Defense Task Force for Business and Stability Operations, and the Afghanistan Geological Survey in the Panjsher Valley emerald, iron, and silver area of interest (AOI) and subareas. The complementary chapters 13B and 13C address hyperspectral data and geohydrologic assessments, respectively, of the Panjsher Valley emerald, iron, and silver AOI. Additionally, supporting data for this chapter are available from the Afghanistan Ministry of Mines in Kabul. The emerald deposits of the Panjsher Valley are the main site for mining gemstone-grade emerald crystals in Afghanistan. The geology of the Panjsher Valley consists of Middle Paleozoic metamorphic rocks represented by a Silurian–Lower Carboniferous marble and Lower Carboniferous and Upper Carboniferous–Lower Permian terrigenous schist. Intrusive rocks include small bodies of gabbro diorite and quartz porphyry and a large intrusion of gneissic granite of the Laghman Complex. The area has an imbricate-block structure elongated to the southwest and northeast. Multiple tectonic events are related to structures within and parallel to the regional-scale Hari Rod fault system. Emerald mineralization in the Panjsher Valley AOI is genetically related to the Laghman Granitoid Complex and is controlled by elongated tectonic zones along the contacts between the carbonate and schist. The Panjsher Valley emerald district contains the following emerald occurrences from the west to east: Khinj, Mikeni I, Mikeni II, Rewat, and Darun. The Buzmal’ Mine is located to the north, close to Panjsher Valley. There are three types of emerald mineralization: (1) mineralization within or adjacent to tectonized diorite dikes (parts of the western zone containing the Buzmal’, Khinj, and Rewat emerald occurrences); (2) mineralization within shear fractures in schist (locality in the eastern zone containing the Darun, Khinj, and Mikeni I and II emerald occurrences); and (3) mineralization in or adjacent to hydrothermally altered and albitized quartz porphyry dikes.

gems, spectroscopy, advanced instrumentation, Raman specrometry, gemology

The current paper gives an overview of the development of Raman spectrometry in gemmological laboratories. While before 1990s, no commercial gemmological laboratory possessed such an instrument, all larger international labs have acquired these instruments by now. The Raman spectrometer is routinely used for the detection of emerald fillers, HPHT treatment of diamonds, analysis of the nature of a gemstone, analysis of gemstone inclusions and treatments, and the characterisation of natural or colour enhanced pearls and corals. Future developments in gemstone research lie in the closer analysis of the features of Raman and PL spectra and in the combination of several instruments.

corundum, geology.11, gems

Colored gemstones such as ruby, sapphire, emerald, and Paraíba-type tourmaline may achieve higher prices when associated with a specific geographic pedigree. Therefore, dealers and collectors increasingly turn to gemological laboratories for country-of-ori-gin analysis. To determine provenance, a laboratory must be knowledgeable about the gems’ geologic formation conditions and types of host rock, crystal growth features, and mineralogical and gemological properties. When the geologic conditions of the primary rock are very similar among several different localities, however, the gemstones’ properties may overlap, rendering origin determination difficult or impossible. Laboratories must meet this complex challenge by extending their observations and analytical capabilities to identify multiple features that yield diagnos-tic patterns to distinguish between similar sources.

corundum, geology.11, gems

Whereas diamonds are mined by large international companies and cut and marketed through a well-established distribution net-work, most high-value colored stones are extracted by independent miners or small companies and sold through less-organized channels. Exploration and grading protocols for ruby, sapphire, emerald, tsavorite, tanzanite, and alexandrite are virtually nonexistent due to the lack of intense research efforts or standardized values on the international exchange. Grading the quality of diamonds on the basis of the 4Cs (color, clarity, cut, and carat weight) is universally accepted and there are virtually no prove-nance-dependent variations in commodity value. With colored stones, though, geographic origin is an important factor for deter-mining price.

gems, ancient gemology, ancient jewelry, Rome, Caligula, glyptic

In the 1990s, a construction project was submitted to the Municipality of Rome for the complete reconstruction of a building and the creation of six underground levels in Piazza Vittorio Emanuele II. Initially a private initiative included in an Urban Recovery Plan, the project was granted a building permit by Department IX in 2001 and later adopted by the Municipality as a public work subject to a Conference of Services, with the aim of redeveloping that part of the Esquiline district. However, the Archaeological Superintendency of Rome expressed serious concerns about the project’s feasibility, as archaeological evidence indicated that the area beneath the building contained remains of the Horti Lamiani. These gardens, destroyed in the late 19th century, were documented by Rodolfo Lanciani and archaeologically reconstructed in 1986 by Eugenio La Rocca and Maddalena Cima in their book Le tranquille dimore degli dei. The site was originally a luxurious residence established during the Augustan era by the consul Lucius Aelius Lamia, later acquired by the imperial domain under Tiberius and used by Caligula as an urban villa (see Suetonius, Caligula 59; Philo Judaeus, Legatio ad Gaium 351 ff.).

corundum, History.1, gems, Indian lapidary

The Preslav gold treasure was found in 1978 near the town of Veliki Preslav, the second Bulgarian capital during the end of the First Bulgarian Kingdom. The 10th-century trea-sure belonged to a female member of the royal family and is believed to be of Byzantine origin. Among the gem materials identified are emerald, violet sapphire, pearl, reddish violet garnet, rock crystal, amethyst, and carnelian. The average dimensions of the emeralds in two medallions were 0.5 cm long and 0.6 cm wide; their origin is suspected to be Egyptian or Austrian based on the deposits known at the time and similarities in their morphology, internal fea-tures, and inclusions. Fine rutile silk inclusions were iden-tified in the sapphire. As the Indian subcontinent was the main source of gem corundum in antiquity and Early Medieval times, it can be assumed that the sapphires in the Preslav treasure are of an Indian or Sri Lankan origin. The barrel-and baroque-shaped saltwater pearls (average 0.4 cm long and 0.5 cm in diameter), some of them partly decomposed, are thought to originate from the Persian Gulf and the coastal areas of the Indian Ocean.

gems, emerald, beryl, Madagascar, Ianapera

The Ianapera emerald deposit is located in the Neoproterozoic Vohibory Block of southern Madagascar. The local geology consists of intercalated migmatitic gneissic units and calcareous metasedimentary rocks, containing boudinaged metamorphosed mafic/ultramafic lenses, all intruded by pegmatite veins. These units occur near the hinge of the tightly folded Ianapera antiform, within a few kilometers of the Ampanihy shear zone. Emerald mineralization is hosted by metasomatic phlogopite veins, and bodies developed within the mafic/ultramafic rocks. Based on field and textural relationships, we distinguish proximal and distal styles of mineralization. Proximal mineralization occurs at the contact of pegmatite veins with mafic/ultramafic units; in the distal style, pegmatites are not observed. Three types of emeralds could be distinguished, mainly on the basis of color and mineral zoning. Some of these emeralds have the most Al-depleted and Cr-rich composition ever recorded. Another characteristic feature to the Ianapera deposit and, to our knowledge, yet unreported, is the association of some emeralds with scapolite in metasomatised mafic rocks. Mineral inclusions are common in most emeralds and include phlogopite, carbonates, barite, K-feldspar, quartz, pyrite, zircon, monazite, bastnaesite, phenakite, plus Fe and Cr oxides. However, feldspar and rare earth element-bearing minerals occur predominantly in proximal emeralds, which also have a more incompatible trace-element signature than distal emeralds. We propose a model related to syn- to post-tectonic magmatic-hydrothermal activity. Pegmatitic bodies intruded units of the Ianapera antiform probably during tectonic relaxation. Exsolution of fluids rich in halogens and incompatible elements from the cooling pegmatites caused hydrothermal metasomatism of Cr-bearing mafic/ultramafic rocks in direct contact with the pegmatites. Local fracturing favored fluid infiltration, permitting the formation of distal mineralization. Emerald composition was controlled by the chemistry of the host rock. The presence of carbonate mineral inclusions in the emeralds and the high F-activity indicated by elevated F-contents in newly formed minerals suggest transport of Be as a fluoride-carbonate complex. It seems likely that beryl formation was triggered by precipitation of F-rich phlogopite, which removed the complexing ligand from the fluid.

gems, beryl, emerald, Egypt

Emerald is a dark-green chromium-vanadium rich variety of beryl, Be₃Al₂Si₆O₁₈. It is the third most valuable gemstone (after diamond and ruby). Beryl is also valued as the major source of the metal beryllium (Be) that has important uses in the nuclear industry. Emerald deposits are known to occur in several countries of the world. Africa produced 1,662 kg emerald in 2005, which represented 31 % of the world production (5,363 kg). Colombia accounted for 46.57 % of the world’s emerald production by volume; Zambia, 20.78 %; Brazil, 20 %; Russia, 7.16 %; Zimbabwe 2.2 %, Mozambique 1.55 %, Madagascar 0.44 %, Tanzania 0.13 %, Somalia 0.02 % and other countries 1.15 %. Other countries with emerald occurrences include Egypt, Nigeria and South Africa. The Egyptian emerald mines are located in the South Eastern Desert about 30 km south of the Red Sea harbor of Marsa Alam. They have an immense historical value, where emerald well known and mined for the first time in the Graeco-Roman period between 30 BC and 312 AD. There are two legendary mines in this region namely: the Cleopatra mines and the Mons Smaragdus. The Egyptian emerald deposits occur mainly in a NW-trending band (45 km long) parallel to the Nugrus Shear Zone. In this study, a total of 10 emerald mineral samples from old mine dumps were chemically analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and XRF for the concentrations of major oxides and 24 trace elements (Cu, Ni, Co, Cr, V, Zn, Ga, Zr, Y, Sr, Rb, Nb, Ba, Pb, U, Th, La, Ce, Sm, Eu, Gd, Tb, Yb and Lu). They have been compared with the other African emerald deposits to determine the geochemical characteristics and construct a genetic model for the emerald mineralization in Egypt. In Africa, emeralds can be distinguished into two main types of geological occurrences and chemical compositions: 1. magmatic or pegmatite non-schist-related emerald mineralization (Egypt, Zimbabwe, Mozambique and Nigeria), 2. hydrothermal-schist-related emerald mineralization (Egypt, Zambia, Madagascar, South Africa and Tanzania). The second type is the most common in Africa. The genetic model for the Egyptian emerald involves the intrusion of granitic pegmatites within Cr-V-bearing serpentines and schists during Pan-African Orogeny (550 Ma). In these deposits, emerald formed through metasomatic processes that involved the addition of elements characteristic of an acid granitic assemblage (Be, alkalis) to a typical ultrabasic assemblage that becomes depleted in Mg, Ti, Cr, Ni and Cu.

gems, beryl, emerald, China, Davdar

gems, beryl, emerald, Egypt, Sikait

The genesis of gem-quality deep green emeralds of Zabara, Sikait and Umm Kabo (South Eastern Desert, Egypt) is to date a controversial topic. The emerald-bearing biotite schists and quartz lenses are interpreted alternatively as a product of (i) thrust-fault-shear zone – controlled large scale alkali-metasomatism driven by post-magmatic fluid flow or of (ii) a large scale interaction between syntectonic pegmatitic magma or hydrothermal fluids with pre-existing basic to ultrabasic rocks, or of (iii) a syn- to post-tectonic regional metamorphism and small scale blackwall metasomatism. Detailed microstructural and chemical analyses of the Egyptian emeralds and their host rocks show that three generations of beryl can be distinguished: a colourless pegmatitic beryl; a pale green Cr-poor beryl crystallized from pegmatite-related hydrothermal fluids; and a deep green Cr- and Mg-rich emerald. The crystallization of the Cr- and Mg-rich emerald was controlled by the very local availability of Cr, Mg and Be-rich metamorphic fluids during the Pan-African tectono-thermal event. Emerald-rich quartz lenses demonstrate that those fluids locally did mobilize quartz, too. The pale green emeralds found within the pegmatites in association with colourless beryl are the product of a mobilization of colourless pegmatitic beryl and/or phenakite by late pegmatitic fluids slightly enriched in Cr by an interaction with the Cr-rich country rocks. The late pegmatitic fluids are typically Na-rich as is demonstrated by the pervasive albitization of the pegmatites. The complex interplay of magmatic and regional metamorphic events during the genesis of the Egyptian emeralds/beryls makes it impossible through stable oxygen isotope data to relate their genesis to the one or the other event.