Abstract: A high-density silica glass article with excellent thermal shock characteristics is formed from a high purity vitreous silica containing an aluminum compound as a crystallization aid and having a dense concentration of cristobalite muclei. The aluminum compound is aluminum oxide, aluminum hydroxide, an aluminum salt, or other aluminum-oxide precursor.A refractory silica glass crucible made according to the invention has remarkable advantages in a Czochralski crystal-growing process. The entire crucible can be crystallized during the initial melt down in the Cz furnace to provide a cristobalite inner surface which effectively resists attack by the molten silicon to minimize contamination problems during crystal growing.Another embodiment of the invention relates to a unique drawn silica glass with good flexural strength having fibrous oriented veins of cristobalite embedded in a matrix of vitreous silica and having remarkable resistance to deformation at temperatures of 1500.degree. C.