Abstract: A nonexplosive chemical composition for gently and noiselessly breaking a rock or concrete mass. The composition comprises a principal component which is prepared by calcining a starting mixture comprising 100 parts by weight of quick lime and 1-20 parts by weight of calcium fluoride. In rock or concrete breaking operations, this composition in the form of aqueous slurry is poured into drill-holes and left to spontaneously hydrate and set with development of expansion pressure. For adequate retardation of the hydration, preferably a second fluoride such as Na.sub.2 SiF.sub.6 which gives CaF.sub.2 by reaction with CaO at the calcination temperature is added to the starting mixture. As an alternatively preferable method for the same purpose, an amino acid compound and/or a lignosulfonate is used as a hydration retarding agent which is mixed with the calcined principal component. Various auxiliary agents may optionally be added to this composition.