The economic return of rock blasting is not provided by brute volume of broken rock, rather by the amount of marketable product. That i s the case of the porphyry quarries of Trento district, whose output is mainly absorbed by road paving and building facing elements production. Blasting at the quarries evolved from heading blast system to parallel holes blasts. A study for the optimal yield geometry, charging and timing of the blasts is synthetically presented, and the underlying criteria are exposed. A model of how explosive acts separating and breaking the rock slabs, and the use of the model in blast design and quarry face orientation is illustrated with examples.
