Strengthened glass articles and method for making

A unitary glass article which is transparent, translucent, or opaque exhibiting exceptionally high flexural and impact strengths composed of an interior glass portion and an integral surface compression layer having a depth of at least 0.001", said surface layer containing crystallites of beta-quartz solid solution which have a coefficient of thermal expansion substantially lower than that of said interior glass portion, said interior portion consisting essentially, expressed in terms of mole percent on the oxide basis, of about 14-24% R.sub.2 O, wherein R.sub.2 O consists of the sum of 0-5% Li.sub.2 O+0-5% K.sub.2 O+the remainder Na.sub.2 O, 17-21% Al.sub.2 O.sub.3, 45-60% SiO.sub.2, 3-6% total of at least one oxide selected from the group consisting of TiO.sub.2 and ZrO.sub.2, and 0-2% P.sub.2 O.sub.5, the sum of R.sub.2 O+Al.sub.2 O.sub.3 +SiO.sub.2 +TiO.sub.2 +ZrO.sub.2 +P.sub.2 O.sub.5 constituting at least 85% of the total composition, and said surface layer containing Li.sup.+ ions in greater amount than in said interior portion with a corresponding decrease in Na.sup.+ and K.sup.+ ions.