Heat treatment of lithic raw material is known from the Middle Stone Age to the Neolithic. These findings require archaeometric techniques and methods for detecting the heat-induced effects within lithic artefacts. However, the existing methods are often cost-intensive and time-consuming, and most of them are destructive. Here, we present a new method using the infrared spectroscopic measurement of the strength of H-bonds formed between surface silanole groups (SiOH) and H2O molecules held in open pores of the samples. The reduction of H-bond strength in chalcedony is shown to be strongly correlated with the loss of open pores induced by heat treatment. Hence, the method is based on measuring one of the transformations aimed for by the instigators of the heat treatment: the reduction of porosity that modifies the rock's mechanical properties. A first application to heat-treated material from the Neolithic Chassey culture (southern France) shows that flint was heated to temperatures between 200°C and 250°C in this period. This has important implications for the study of the procedures used and the heating environments. Our new method is non-destructive, rapid, cost-effective and allows for detection of the used annealing temperatures.