Growth defects and growth marks in pegmatite beryls
Scandale, Eugenio; Lucchesi, Sergio; Graziani, Giorgio
European Journal of Mineralogy Volume 2 Number 3 (1990), p. 305 - 312
published: Jun 21, 1990
manuscript accepted: Feb 15, 1990
manuscript received: May 20, 1989
ArtNo. ESP147050203006, Price: 29.00 €
Abstract Pegmatite beryl crystals are studied by X-ray topography methods, optical and scanning electron microscopy and electron microprobe analysis. Topographs show quite perfect crystals characterized by the absence of basal dislocations and by five growth stages. Minor element concentrations suggest that P-T variations occurred mainly during the first three growth stages, by contrast, the chemical evolution of the environment must also be taken into account for the last stages. The remarkable ondulatory extinction of one sample is related to superficial grooves caused by corrosion of dislocation bundles. The present observations, taken as a whole, indicate that structural defects in beryls from pegmatites are characteristic features of their particular growth environment and can therefore be considered as growth marks.