Иностранный язык в сфере профессиональных коммуникаций (геммология). Составители: Шмакин Б. М., Золотарева Е. В
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AquamarineThe major source of gem aquamarine continued to be Minas Gerais, Brazil, where aquamarine is a principal constituent of numerous weathered pegmatite deposits. The states of Espirito Santo, Bahia, Ceara and Rio Grande do Norte also produce commercial quantities of aquamarine. During the decade of the 80s, additional significant amounts of gem-quality aquamarine were found in Nigeria, Zimbabwe, Zambia, Namibia, Madagascar, Pakistan, India and Transbaikal part of Russia. Much of the material from Nigeria emerges from the ground in classic aquamarine blue, and does not require (no respond to) the heat treatment routinely used on the greener Brazilian material. MorganiteThe pegmatites of Minas Gerais provide most of the morganite on the world market. While the Urucum deposit continued to produce, a major find was made near Salinas in 1986. This occurrence, known as the Bananal mine, produced many large, bicolored morganite-aquamarine crystals. Many of these crystals contained large nodules of virtually flawless morganite at their centers – the first reported occurrence of gem nodules in a material other than tourmaline. Early in the 7th decade of 20 century, significant amounts of light orange morganite were also mined in Mozambique, but supplies have been erratic in recent years because of the political turmoil in that country. ChrysoberylThe gem fields of Sri Lanka continued to be the major source of fine chrysoberyl, particularly cat’s-eye material. Alexandrites were occasionally found as well. However, the 1980s saw several major new finds of chrysoberyl, cat’s-eye chrysoberyl, and alexandrite in Brazil. Cassedanne discusses the main localities and their geologic settings. Proctor describes the exciting discoveries of alexandrite in Minas Gerais, first in the Malacacheta region (1975) and then at the deposit near Lavra de Hematita (1986). The latter occurrence has furnished some of the finest alexandrite ever found. Although Russia has historically produced fine chrysoberyl and alexandrite, no reliable production information for this decade is available. RubyThe classic ruby occurrences of Southeast Asia (i.e., Mogok, Burma (Myanmar), Chanthaburi, Thailand and Pailin, (Cambodia) continue to be major producers of ruby, but the 1980s also saw the exploitation of new occurrences in East Africa, specifically Kenya, Tanzania, and, more recently, Malawi. Although the quality of material from these African localities may be not always equal to that of stones from Southeast Asia, it is regularly encountered in the trade. Small amounts of ruby have also come from Pakistan, Afghanistan, India, and Nepal. SapphireAs with ruby, much of the sapphire in the jewelry trade today comes from Southeast Asia. Significant amounts continued to be found in Sri Lanka and Burma, with the Cambodian deposits largely remaining dormant until the end of the decade. The sophisticated operation at Kanchanaburi, in southwest Thailand, is a major new producer of natural-color blue sapphire. Two localities played a major role in the greater availability of sapphires: Australia and East Africa. Although both Queensland and New South Wales have long been known as sources of gem sapphire in a wide range of colors, only within the last 20 years did they reach a significant level of commercial production. In East Africa, expanded production was seen from Kenya, Tanzania, Malawi, Burundi, and Rwanda. Particularly noteworthy are the sapphires found along the Umba River in Tanzania, which occur in a wide range of colors, with the orange and color-change varieties being especially interesting. In 1981, for the first time in almost four decades, westerners visited the historic Kashmir deposits. Although it appears that these famous deposits still have significant mining potential, there has been little recent production. GarnetGem garnet continue to be produced from numerous major deposits in India, Sri Lanka, Mozambique, and Madagascar, but the most exciting development was the emergence of East Africa as a principal source and the discovery there of a number of “new” species and varieties of this complex gem group. Following the discovery of green grossular “tsavorite” in both Kenya and Tanzania in the early 1970s, this region continued to produce gem garnet in a range of composition and color beyond that previously encountered. Among these remarkable new types are the reddish brown “malaya” garnet, which has been shown to be members of a solid-solution series between pyrope and spessartine. East Africa also produced quantities of previously rare color-change garnets as well as unusual hues such as “raspberry” rhodolites. OpalThe major source of gem opal continued to be Australia and, specifically, the territories of New South Wales, South Australia, and Queensland. Mining activity at White Cliffs, New South Wales, famous for “crystal opal” (a transparent, colorless variety that displays intense play-of-color), was revitalized by the introduction of heavy equipment. Lightning Ridge, best known for black opal, showed a small increase in production, also due to improvements in mining techniques. One of the more interesting developments was the mining of commercial amounts of contraluz, hydrophane, and rainbow opal at Opal Butte, Oregon. Some unusual colors of opal, including green and blue, came from Piaui, Brazil. Discovered in the 1960s, green opal from Tanzania first became available in commercial quantities. Traditional deposits elsewhere in the U.S. and in Mexico continued to be active. SpinelSpinel came principally from traditional sources, including both primary and secondary deposits in Southeast Asia (Burma, Cambodia, and Thailand) and secondary (alluvial) deposits in Sri Lanka. Some material also came from Tanzania and Brazil. Characterization of material from old and some new localities led to a better understanding of the causes of color and the range of properties among gem spinels. For example, investigators saw the first description of color-change spinel. Anderson, Jackson, and Schmetzer and Bank reported the properties of gem-quality, zinc-bearing gahnite and gahnospinel from Nigeria and Sri Lanka. In the mid-1980s, demand for red spinel increased dramatically as it gained appreciation as a medium-priced red stone. One of the newest and most promising developments has been the discovery of exceptionally large, transparent pink spinels from the Pamir Mountains of the former Soviet Union. Amethyst and Citrine Brazil was the major producer of fine amethyst and citrine. Amethyst occurs in both igneous and sedimentary geologic environments, principally in the states of Paraiba, Goias, Ceara, Bahia, Minas Gerais, and Rio Grande do Sul. Epstein described the occurrence of amethyst in fractures in quartzite in Maraba, the alluvial deposit at Pau d’Arco, and the mining of amethyst geodes from basalt near Santa Maria and at Irai. Amethyst is also produced in Uruguay in colors comparable. New were major deposits of intensevely colored, reddish purple amethyst in Zambia. As is the case in many Third World countries, the rough crystals must be purchased through a state agency, in this instance known as Mindico. A new locality near Port Hedland in Western Australia has also produced fine material. The great majority of citrine available was actually heat-treated amethyst from Brazil. One of the most interesting materials to emerge in the gem market was bicolored amethyst-citrine (“ametrine”). Although reports speculated that these stones were produced by treatment, crystals displaying both colors have been confirmed from a deposit known as La Gaiba, in the Rincon del Tigre region of Bolivia, near the border with Brazil. жүктеу/скачать 1.37 Mb. Достарыңызбен бөлісу:
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