Resumo

NEWMAN, José Albino et al. Mineralogicalcharacterization of the diamond of the alluvial placer from Icabaru River, Santa Elena de Uairén, Bolivar State, Venezuela. Rev. Asoc. Geol. Argent. [online]. 2009, vol.64, n.3, pp.472-480. ISSN 0004-4822.

Mineral characterization consisted on the study of 458diamond samples representative of gem-grade and industrialgrade varieties,obtained from alluvial (placer) diamond exploration located in the Icabaru and Uaiparu Rivers, Santa Elena de Uairén. Mineral analyseswere predominantly focused on physical properties and average weight (0.2 and 1.0ct). Optical microscopy was used to study surface sections of diamonds andmorphological characterization which resulted in the following. In relation tocolor, distribution percentages were colorless (37%), yellow (20.5%), brown(19%), green (9,5%), black (3%), green lattice points (7.5%), and brown latticepoints (3.5%). Also, a polycrystalline variety known as carbonado, orblack diamond, was studied. Some surface shapes such as trigons, quadrilateral,block and film growth, groove and hillocks were determined through ScanningElectron Microscopy (SEM) and Energy Dispersive Spectrometer technique (EDS).Morphological evolution could be established from the octahedral primitivethrough dissolution phenomena for (111)+(110), (111)+{hkl} facets having rhombicdodecahedron {hkl} and hexaoctahedron {110} habits. Chemical composition datawere collected through Infrared Absorption Spectroscopy (FTIR), and diamondtypes were determined Ib with low nitrogen concentration, IaA, IaB and IaAbdiamonds with high, average and low nitrogen concentration and IIa diamondswith no nitrogen concentration. Inclusions of olivine, ilmenite and garnet onthe crystal surface were detected by micro-Raman spectroscopy.

Palavras-chave : Diamond; Icabarú; Group Roraima.

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