Original scientific paper
Crystal morphology and xrd peculiarities of brazilianite from different localities
Andrea Čobić
orcid.org/0000-0002-3805-0594
; Faculty of Science, Institute of Mineralogy and Petrography, Horvatovac 95, Zagreb, Croatia
Vladimir Zebec
; Croatian Natural History Museum, Demetrova 1, Zagreb, Croatia
Ricardo Scholz
; Department of Geology, School of Mining, Federal University Ouro Preto, Ouro Preto, MG, Brazil
Vladimir Bermanec
; Faculty of Science, Institute of Mineralogy and Petrography, Horvatovac 95, Zagreb, Croatia
Sandra de Brito Barreto
; Department of Geology, Federal University of Pernambuco, Av. Academico Hélio Ramos. S/N. 5 andar., Cidade Universitária, Recife, PE, Brasil
Abstract
Forty 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.
Keywords
brazilianite; morphology; two-circle goniometer; Brazil; Canada; Rwanda
Hrčak ID:
69826
URI
Publication date:
30.6.2011.
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