The aim of this work was to study opacity variation throughout Brazilian production of rocky quartz fragments and analyze the impact of opacity on fused silica glass properties, more specifically bubble formation and size. To accomplish that, 32 samples were collected and their opacities were evaluated by measuring the light absorption coefficient of each sample. 10 of those samples were then flame fused and the size of formed bubbles was measured on the glass using a microscope. The bubble size measurements were compared with those of commercial powders fused by the same method. Results show that significant variations in opacity exist in the production process and better quality control is required in order to meet international standards. Regarding bubble formation, samples with light absorption coefficient lower than 150 cm(2)/kg can generate glasses with bubble size close to those observed on glasses made using commercial powders. (C) 2013 Elsevier B.V. All rights reserved.