DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Resultados da Pesquisa
Item Pseudomorphs of low microcline adularia fourlings from the Alto da Cabeça (Boqueirão) and Morro Redondo pegmatites, Brazil.(2012) Bermanec, Vladimir; Horvat, Marua; Gobac, Željka Žigovečki; Zebec, Vladimir; Cipriano, Ricardo Augusto Scholz; Škoda, Radek; Wegner, Reinhard; Barreto, Sandra de Brito; Dodony, IstvanPotassium 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.Item Crystal morphology and xrd peculiarities of brazilianite from different localities.(2011) Čobić, Andrea; Zebec, Vladimir; Cipriano, Ricardo Augusto Scholz; Bermanec, Vladimir; Barreto, Sandra de BritoForty four brazilianite crystals from several localities in Brazil, Rwanda and Canada were measured on a two-circle goniometer to determine brazilianite morphology. Twenty forms were recorded; six of them have not been recorded before. All faces in the [001] zone are striated along crystallographic axis c. All striated forms in the [001] zone exhibit multiple signals. Two of the signals observed on the form {110} are always very clear. There is an exception on one crystal where just one face, (110), exhibits only one clear signal. Five groups of habits were recorded, two of them new to this mineral species. Eleven samples were examined by X-ray diffraction for calculation of the unit cell parameters yielding a=11.201(1)–11.255(2) Å, b=10.1415(5)–10.155(1) Å, c=7.0885(7)–7.119(2) Å and b=97.431(7)–97.34(1) °. All X-ray diffraction patterns show a peculiarity: some diffraction lines are widened or doubled with the appearance of additional diffraction lines systematically on lower °2Q. These diffraction lines have smaller intensities and cannot be indexed in accordance with brazilianite crystal structure.