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| Ferreira,Ana C.M.; Ferreira,Valderez P.; Soares,Dwight R.; Vilarroel-Leo,Hugo S.. |
| The Alto Quixaba pegmatite, Seridó region, northeastern Brazil, is a 60º/80ºSW-trending subvertical dike discordantly intruded into biotite schists of the Upper Neoproterozoic Seridó Formation. It has three distinct mineralogical and textural zones, besides a replacement body that cuts the pegmatite at its central portion and in which occur, among other gem minerals, colored elbaites. Elbaites usually occur as prismatic crystals, elongate according to the c-axis, with rounded faces and striations parallel to this axis. Optically, crystals are uniaxial negative with strong pleochroism; refractive index extraordinary axis = 1.619-1.622 and ordinary axis = 1.639-1.643, birefringence between 0.019 and 0.021, average relative density of 3.07, and the following... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Elbaite; Tourmaline; Seridó pegmatitic province. |
| Ano: 2005 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652005000400011 |
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| Soares,Dwight R.; Beurlen,Hartmut; Ferreira,Ana C.M.; da-Silva,Marcelo R.R.. |
| Gahnite electron probe microanalyses from three pegmatites (Mirador, Capoeira and Quintos) of the Borborema Pegmatitic Province in northeastern Brazil allowed to determine molar compositions ranging from 86.22 to 95.41 mol% gahnite (ZnAl2O4), 1.51 to 6.62 mol% hercynite (Fe2+Al2O4), 0.11 to 5.89 mol% spinel (MgAl2O4), 1.48 to 2.74 mol% galaxite (MnAl2O4), and Zn/FeTotal atomic ratios ranging from 11.53 to 60.87. These data compared with gahnite compositions from albite subtype pegmatites from Cap de Creus, Spain (Zn/FeTotal between 10 and 60) and from the source granite of the Separation Rapids pegmatite field, Ontario, Canada (Zn/FeTotal =3.5) indicate a high degree of fractionation of the studied pegmatites. This interpretation agrees with conclusions... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Gahnite; Rare-element granitic pegmatites; Borborema Pegmatitic Province; Mineral chemistry. |
| Ano: 2007 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652007000300005 |
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