Even if stones like flint, obsidian, basalt, etc., have similar mechanical properties, empirical flaking stone experiences in prehistorical research have shown us that there are important behavior differences for the stone knapper who flakes them. The aim of this work was to calculate these differences not empirically but quantitatively. Elasticity and isotropy appeared as the more important mechanical properties to measure. We tested several analytical methods. The ultrasonic method with stationary waves seems the best one to solve this kind of problem. Thanks to this method weak elasticity or isotropy variations can be tested with great precision. In the future this may help solve some problems in lithic technology, in functional stone tool analysis, and in raw material choice. -- AATA