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Título: | Pseudomorphs of low microcline adularia fourlings from the Alto da Cabeça (Boqueirão) and Morro Redondo pegmatites, Brazil. |
Autor(es): | Bermanec, Vladimir Horvat, Marua Gobac, Željka Žigovečki Zebec, Vladimir Cipriano, Ricardo Augusto Scholz Škoda, Radek Wegner, Reinhard Barreto, Sandra de Brito Dodony, Istvan |
Palavras-chave: | Low microcline Adularia Granitic pegmatite Pseudomorph |
Data do documento: | 2012 |
Referência: | BERMEC, V. et al. Pseudomorphs of low microcline adularia fourlings from the Alto da Cabeça (Boqueirão) and Morro Redondo pegmatites, Brazil. Canadian Mineralogist, v. 50, p. 975-987, 2012. Disponível em: <http://www.canmin.org/content/50/4/975.abstract>. Acesso em: 20 de jun. 2017. |
Resumo: | Potassium feldspar crystals from the Alto da Cabei;:a (Boqueiriio), Rio Grande do Norte (sample BQ) and the Morro Redondo, Minas Gerais (sample MR) pegmatites in Brazil bave a typical adularia fourling habit consisting of a combination of Baveno and Manebach twins. Crystal morphology suggests a monoclinic symmetry, but XRPD measurements and TEM experiments show that the samples are low microcline. Calculated values of triclinicity [A = 0.915 (BQ) and A = 0.9225 (MR)], cell parameters [a8.587(4), b 12.969(4), c 7.223(2) A, o: 90.66(3) 11 115.97(4), 'I 87.69(3)0 for BQ and a 8.584(3), b 12.970(3), c 7.225(2) A, o: 90.66(3) 11 115.97(3), 'I 87.74(3)0 for MR), t1o occupancy of A! [0.99 (BQ) and 0.98 (MR)], order index [dsM = 0.97 (BQ) and dsM= 0.99 (MR)] and IAI at the T1 sites [98.6% (BQ) and 99.5% (MR)] reveal a triclinic syrnmetry and a high state of order for the sarnples of potassium feldspar. Transmission electron microscopy and selected-area electron-diffraction investigations of the crystals show that they are compositionally homogeneous, without exsolution larnellae of other phases. The electron-diffraction pattems show no splitting of any refiection and no streaking, and thus indicate ideal order in both sarnples. According to crystal morphology and the results on submicroscopic scale, we conclude that in this case adularia sarnples bave a completely ordered structure. The measurements and calculations demonstrate that they are highly ordered, i.e„ maximum microcline. Adularia pseudomorphs are highly ordered triclinic feldspar developed through transformation of a monoclinic pareni. |
URI: | http://www.repositorio.ufop.br/handle/123456789/8309 |
Link para o artigo: | http://www.canmin.org/content/50/4/975.abstract |
DOI: | https://doi.org/10.3749/canmin.50.4.975 |
ISSN: | 1499-1276 |
Aparece nas coleções: | DEGEO - Artigos publicados em periódicos |
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ARTIGO_PseudomorphsLowMicrocline.pdf Restricted Access | 1,34 MB | Adobe PDF | Visualizar/Abrir |
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