corundum, geology.11, gems

Based on mineralogic and geologic research on corundum occurrences in Russia, and published data on corundum localities occurring elsewhere, it is emphasized that regional metamorphism of different rock types (e.g., marble, gneiss) is the major factor controlling the formation of corundum deposits and determining the quality of the gems they contain. The chemical and physical properties of the metamorphic host rocks ultimately determine the characteristics of gem corundum. The sapphires from Kashmir and rubies from Myanmar, which formed in metamorphic environments, are cited as examples. The superb gems from these deposits had the appropriate chromophoric elements available during their formation, under the proper metamorphic conditions. Characteristic mineral inclusions are considered indicative of specific genetic types of corundum, and, for alluvial stones, the inclusions can be used to infer the origin of the gem corundum. Gem corundums originating from other geologic sources (e.g., igneous or metasomatic) are likely to be of lower quality than those of metamorphic origin.

corundum, treatments.6, gems

gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology, Pre-Columbian jade; Costa Rica; Maya; exchange; iconography, lapidary

A finely carved jade “spoon,” curated in the artifact collection of the Belize Department of Archaeology in Belmopan, is described. The distinctive artifact, whose precise archaeological provenience is unknown, is compared with similar jade spoons identified elsewhere in Mesoamerica and Lower Central America. It is concluded that the Belize jade spoon dates to the Middle Preclassic period (900–350 BC) and is most likely of Olmec origin. The jade spoon was discovered at the site of Uxbenka in the Toledo District of Belize. The artifact was found by the site caretaker on the surface of the main plaza, near a looted Classic-period tomb. After its discovery, the caretaker delivered the jade piece to a Toledo District official for transfer to the Belize Department of Archaeology in Belmopan, where it is now housed. Uxbenka, meaning “old village” in Mopan Maya, is located near the village of Santa Cruz, approximately 15 kilometres east of the Belize–Guatemala border. Norman Hammond located two building groups associated with Uxbenka, which he called Sta. Cruz North, while conducting a site survey near Lubaantun in 1971. The site was reconnoitred by Belize government archaeologists and Richard Leventhal in 1984. Records in the Archaeology Department indicate that looters had trenched the largest structure and partially destroyed, while leaving open, the aforementioned tomb on the south side of the main plaza. Following reports of continued looting in the area, Leventhal conducted salvage excavations at Uxbenka, produced the first map of the site core, and recorded the remains of numerous stelae in the main plaza. Several of the stelae retain evidence of original painting. Three stelae are dated stylistically to the Early Classic period and are among the earliest carved monuments known from the southern Belize subregion. Prior to the discovery of the jade spoon, there had been no reported evidence of Formative-period occupation at Uxbenka. The Uxbenka jade was examined by the authors at the Belize Department of Archaeology in Belmopan, where it is presently stored in the government archaeological vault (Cat. No. 27/179-6:21). The piece was studied, photographed, and illustrated by members of the Trent University Preclassic Maya Project laboratory in San Ignacio. The jade measures 18.5 cm in length, 6.8 cm in width, and has a maximum thickness of 1.5 cm. No weight was recorded. The artifact is finely carved, smoothed, and polished to a low lustre. It is bluish-green in colour with tiny whitish flecks. The form is that of a right-facing “spoon,” or tadpole, with three concave depressions on the front separated by rounded ridges. The reverse side is slightly rounded. Three evenly spaced biconical drill holes run from the back to the upper edge, although only the central drill hole is visible on the front.

gems, Somalia, Somaliland, ruby, sapphire, garnet

Recent geological surveys indicate that Somaliland has abundant deposits of gemstones, from emerald to aquamarine, ruby and sapphire as well as vast amounts of garnet, quartz and opal, and lesser-known minerals such as titanite and vesuvianite. Somaliland in northern Africa appears to be the new potential gemstone-bearing area comparable to Madagascar or Tanzania. In addition to pegmatite, which are the host rocks of emerald and other kinds of beryl such as aquamarine, Somaliland has metamorphic rocks that hold nodules of ruby and sapphire. There is little understanding of its mineral deposits, but villagers in Somaliland use primitive tools to dig out a range of gemstones that they offer for sale to dealers locally. When aid officials at the European Community (EC) office in the capital, Hargeisa, first saw the gemstones, they believed they had been stolen from graves. To determine whether these stones came out of the ground or were stolen, EC invited Dr. Judith Kinnaird, a consultant geologist and gemmologist from the University of Witwatersrand in Johannesburg, to investigate. Dr. Kinnaird visited the country twice and, in addition to identifying gem minerals, she helps local miners distinguish among similar coloured minerals and is working with Progressive Interventions (supported by EC funding) to help set up a gemmological association and marketing channels. Somaliland is part of the Mozambique Belt and was formerly part of the same landmass as Madagascar, Tanzania, Sri Lanka and India prior to continental drift. Recovery of gemstones began only in 1988 and is still carried out in a primitive and haphazard manner. The gem-producing belt is a narrow strip between 30 and 80 km wide and 200 to 300 km long, running roughly parallel to the Gulf of Aden. The country, once a British protectorate, suffered a nine-year civil war from 1982, leaving infrastructure like roads and bridges in disrepair. Dr. Kinnaird described access to gem deposits as difficult and hazardous. The terrain includes high mountains and coastal regions with temperatures reaching up to 50°C. Two emerald-producing areas, Alihiley and Simodi, occur at the contact of pegmatite and chromium-bearing schist. Patchy colour development and dual-colour zoning were observed in crystals. At Simodi, pegmatite is visible across the hillsides, and emerald is being mined again after years of inactivity, despite dangerous pit conditions and lack of equipment. In Alihiley, rudimentary mechanical tools like a compressor are used. East of the emerald belt, aquamarine and other beryls occur in pegmatite intruding granite, giving rise to large but often cracked crystals coloured by iron or titanium. Reports also mention yellow beryl (heliodor). Ruby and sapphire are found in metamorphic rocks, not pegmatite. Ruby has been found in red corundum cores with green zoisite, while sapphire occurs in nodules, greenish-blue near the surface and better-quality blue material at depth. Unlike other African countries, ruby and sapphire are not found together. Garnet is extremely abundant, in red to orange colours and of multiple types, including pyrope and almandine, and some green garnets initially mistaken for Tsavorite were identified as vesuvianite. Orange to yellow opals lacking play-of-colour have been found, but high-quality reddish opal with good play-of-colour also occurs, possibly in both lava and gypsum/anhydrite strata. Quartz is widespread, including high-purity rock crystal, smoky quartz, banded forms, and deep purple amethyst. Additional minerals include red spinel, watermelon tourmaline, colourless topaz, blue and green vesuvianite, titanite, apatite, and zircon. Some locals mistake quartz for diamond, though Dr. Kinnaird clarified there are no diamonds in Somaliland.

gems, jade, jadeite, fei cui, China

corundum, Inclusions.5, Tanzania.12, Madagascar.12, gems

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

In Mesoamerica, various raw materials were used for the manufacture of tools and utensils, among which jade stands out, being used primarily for the production of luxury objects. The Motagua Valley in Guatemala is the only place known in Mesoamerica where jade was extracted. This region has been little studied; in this work, the aspects that have been investigated, as well as descriptions and the locations of jade outcrops, will be presented. Likewise, a definition of objectives for the study and protection of this mineral and cultural resource of Guatemala will be proposed.

gems, history of gemology, Pliny, Rome, Roman mineralogy, Roman science, history of science

The Elder Pliny's Natural History provides a wide-ranging account of human achievement in the arts and sciences in the first century AD. This book re-examines Pliny's work for the first time since the 1920s. Modern experiments, simulating the techniques described by Pliny, and an in-depth study of his development of a technical language, confirm his unique contribution to our knowledge of science in early imperial Rome.

gems, lapis lazuli, Afghanistan, history of gemology, gem trade, Central Asia, archaeology, archaeogemology

Lapis lazuli was the true precious stone of the ancient Near East—a key symbolic element in both the Near East and Egypt—its possession was a mark of political and religious power. Its history, which began as early as the Neolithic period (in the 7th millennium), continued into the Bronze Age up to the 2nd millennium B.C. and beyond. It is attested at sites more than 3,000 km apart, from Central Asia to Mesopotamia, and from Syria to Egypt. It is a rare rock, difficult to obtain due to its origin in very high mountains with access limited by natural conditions. The lapis lazuli worked in the ancient Near East came from the Badakhshan mines (Afghanistan), from Gorno-Badakhshan in the Pamirs (Tajikistan), and possibly from the Chagai Hills (Pakistan). Lapis lazuli saw its greatest use in the mid-3rd millennium, as shown by the fabulous wealth of the Royal Cemetery tombs at Ur. The study of manufacturing debris and tools indicates the existence of a shared sequence of production steps for making lapis lazuli ornaments. Regional styles emerged depending on whether the adornments came from Egypt, Syro-Mesopotamia and Susiana, or from Iran (outside Elam) or Central Asia. The hierarchical city-states of Syro-Mesopotamia were major consumers of symbolic goods, which also served their propaganda. Craftsmen worked within workshops dependent on palaces or temples. The Epic of Gilgamesh shows the gods equipping favored beings with lapis lazuli or providing them with protections before entering the underworld. Lapis lazuli symbolizes the life force that is the source of divine power. It is both agent, sign, and manifestation of the circulation of goods, ideas, and cultural representations, as well as of relationships of influence, domination, and exchange among the centers of Near Eastern civilization from the 4th to the 2nd millennia B.C.

corundum, synthetic corundum.7, gems

Gemological investigations of Tairus hydrothermal synthetic ruby revealed characteristic microscopic features, including solid alloy inclusions consisting mainly of copper–iron alloys and wavy growth lines. Chemical analysis by microprobe showed that the chromium concentration in the area of the growth lines averaged 3.81 wt.% Cr₂O₃, as compared to 1.53 wt.% Cr₂O₃ in the remainder of the stone. Characteristic infrared absorption peaks are 3308, 3233, and 3186 cm⁻¹.