Growth defects in a quartz druse <a+c> dislocations

Growth defects have been studied by X-ray topography in two natural quartz crystals from a Brasilian druse. Different types of defects have been observed and they showed similar configuration in both samples. Dislocations are analyzed and discussed. In particular, `pyramidal' dislocations with (a +c) Burgers vectors have been characterized: these uncommon dislocations are analyzed in detail because even today they are believed to be nucleated only by deformation processes. The observations, taken as a whole, indicate that defects of crystals from a druse present distinctive characteristics.