Alkali Silica Reaction (ASR) is a frequent cause of reduced durability of concrete.It is known that one main reason for this type of damage is the increased solubility of strained quartz aggregates under ASR conditions.Many attempts are made to characterize or test aggregates with respect to ASR risk.Defined durability tests on concrete prisms (ASR performance tests) are now required in Germany for obtaining a permission to apply aggregates for highway pavement concrete.In order to characterize aggregates, thin sections are frequently investigated by light optical microscopy.On this way in principal the deformation regime of the quartz microstructure can be assessed.Due to the describing nature of thin section microscopy a real measurement of quartz deformation properties, i.e.dislocation density, preferred orientation etc.cannot or only with great effort (U-stage measurements to determine nreferred orientation of auartz-axis) be done.