Navegando por Assunto "Jadeíta"

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Acesso aberto (Open Access)
Mineralogy and chemistry of the green stone artifacts (muiraquitãs) of the museums of the Brazilian State of Pará
(2012-03) MEIRELLES, Anna Cristina Resque; COSTA, Marcondes Lima da
Muiraquitãs, lithic artifacts found in the Amazon basin, have been considered to be Asian in origin, or to have been sculpted by the legendary female Amazon warriors. These pieces are now very rare, and are found mainly in museum collections. In the present study, the mineralogical and chemical content of 23 specimens from the collections of the Museu de Gemas (Gemstone Museum) and Museu do Encontro (Meeting Museum) in Belém, Brazil, were analyzed. Most of the pieces were made of minerals commonly found in Brazil - quartz, albite, microcline, variscite, anorthite, and tremolite (the equivalent of nephritic jade). However, four of the pieces were made of jadeite, that is, jadeitic jade, which is unknown in the Amazon basin or in other parts of Brazil. The confirmation of the presence of this mineral in some of the artifacts reopens the debate on the mineralogical origin of the muiraquitãs found in the Amazon basin. Before the present discovery, their origin was defended as Amazonian due to the absence of jadeite jade in the searched pieces and the fact that jadeite was not found in Brazil but in Central America and Asia.
Acesso aberto (Open Access)
Muiraquitã e contas do Tapajós no imaginário indígena: uma análise químico-mineralógica dos artefatos dos povos pré-históricos da Amazônia.
(Universidade Federal do Pará, 2011-08-25) MEIRELLES, Anna Cristina Resque; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; 1639498384851302
The muiraquitãs, also known as greenstones, are stone artifacts which are carved meticulously into batrachian shapes. These artifacts constitute one of the most prominent symbols of pre-colonial Amazonian culture. These objects are made from extremely hard rocks or minerals. The term muiraquitã was first discussed by Rodrigues (1875) following his exploration of the region of the Nhamundá River. As jade is unknown in the Amazon basin, the muiraquitãs were traditionally considered to represent vestiges of ancient Asian cultures. In recent years, they have become very rare museum pieces, but there is virtually no information on their origin or significance. Even so, analysis of the texture of the surface of these artifacts has permitted the identification of some of the techniques used in their production, which has contributed to the understanding of the productive process. Morphological studies of 17 pieces deposited in the Gemas (Gemstone) and Encontro (Meeting) museums of the Brazilian city of Belém found that three principal groups could be distinguished on the basis of the carving process, which had four stages: paring, perforation, carving, and polishing. In one piece (510), it was possible to identify the use of a rotary tool with a rare abrasive. The results of the mineralogical and chemical analysis of 22 muiraquitãs indicated that they are constituted of one or more of the following minerals: quartz, tremolite, tremolite-actinolite, variscite-strengite, anorthite, albite, and microcline, which are all common materials in any part of Brazil. The predominance of quartz was confirmed by the chemical composition, basically SiO2. In the collection of the Meeting Museum, however, the most intriguing and widely-discussed mineral of all was discovered – jadeite, the constituent of jadeite jade. This mineral was found in pieces 518, 519, 524, and 525. Its percentages of SiO2 (58.6-67.1%), Al2O3 (20-24.7 %), and Na2O (8.8-15.5%) are equivalent to those of the jadeites of Montagua. The confirmation of the presence of jadeite in these pieces from the Meeting Museum reopens the discussion of the mineralogical origin of the muiraquitãs found in the Amazon. The coloration of these pieces vary in their shades of green, from white to greenish, yellow-green, olive green, and milky hues, to dark green, almost black. The predominant color is light green, with “veins” of slightly darker or lighter coloration. The pieces made from tremolite, quartz, amazonite, and jadeite are very hard (generally 5 or 6, but up to 7), and their measurements are: length (44-64 mm), width (22-57 mm), and thickness (15-19 mm). In addition, the mineralogy of 16 beads and 12 pendants belonging to the Mário Simões technical collection of the Goeldi Museum was analyzed. The results indicate that these pieces were normally made of a single mineral, including tremolite, tremolite-actinolite, calcite, quartz, muscovite, hematite, dolomite, and kaolinite, minerals typical of the composition of rocks, such as schists, gneisses, and granitoids, which are amply distributed in the Amazon basin. A combined analysis of the mineralogical composition of the pieces and the geographic location of the finds permitted the conclusion that the artifacts made of greenstone (tremolite or termolite-actinolite) were more widely-dispersed and possibly also of greater prestige, extending from the lower Amazon basin, in the proximity of the Tapajós and Trombetas rivers, as far as the mouth of the Amazon in Amapá. The pieces made of calcite or quartz+muscovite+microcline were found within a more restricted area, in the present-day municipality of Santarém. The raw material for the majority of the pieces investigated – muiraquitãs, beads or pendants – was Amazonian in origin, being found in the crystalline Archean and Proterozoic terrains located both to the north and south of the Amazon, and outcropping in the riverbeds of its tributaries, except for the specimens carved out of jadeite. It was possible to confirm that the peoples of the lower Amazon basin distinguished between harder, brighter and more transparent rocks, which were used mainly for the production of muiraquitãs, while the beads and pendants were made from greenish rocks used to compensate the rarity of the true greenstones, which are generally more difficult to obtain.