A rock cracking assembly comprising a non-primed cracking cartridge and a detonator comprising a tubular detonator sleeve of a polymeric material, said detonator sleeve having a closed nose portion in a front end, a closed rear portion, a series of detonator members including an igniter which can be ignited electrically, and a detonator charge provided in a main part of the detonator sleeve between said rear portion and said nose portion in order to be fired by the igniter, which main part can be introduced into the cracking cartridge in order to prime the cracking cartridge, wherein - the non-primed cracking cartridge comprises an outer sleeve with an end wall in a first, front end and a plug which closes the outer sleeve in a second, rear end, said outer sleeve, said end wall, and said plug between them defining a main chamber which has a first volume, - said plug has a central channel which prior to the priming of the cracking cartridge is closed by a sealing membrane, - a cracking powder charge, in a compressed state thereof, has a second volume, - said main part of the detonator sleeve which can be introduced into the cracking cartridge has a third volume, - said second and third volumes together correspond to said first volume, - said sealing membrane in said plug can be penetrated by the detonator as the nose portion of the detonator is pressed with force against the sealing membrane, and the outer surface of the detonator sleeve and a second section of said central channel have circular concentric shapes, allowing the main part of the detonator sleeve to be introduced into the cracking cartridge such that the cracking powder charge is pushed aside by the detonator sleeve and is caused to completely fill the space between said outer sleeve, said detonator sleeve, said end wall, and said plug, wherein said second section of the central section is a front tubular section, and in that, as the detonator /the detonator sleeve successively is moved further into the space and soon also is pressed into the powder charge, the powder is pressed aside and is increasingly compacted at the same time as air, which exists in the space is pressed out through the not yet completely closed central channel in the plug, and finally, the rear portion of the detonator sleeve, which has a larger diameter than the main part of the detonator sleeve which has a diameter, is pressed into said second front tubular section in the plug with sealing contact between the rear portion and the second front tubular section until a flange of the rear portion is pressed against shelves provided in the regions of spacing members of an external part of the plug and against upper surface areas of the plug between the spacing members, hence, at the same time as the rear portion of the detonator sleeve and said second front tubular section of said central channel are brought into sealing contact with each other. - the non-primed cracking cartridge comprises an outer sleeve with an end wall in a first, front end and a plug which closes the outer sleeve in a second, rear end, said outer sleeve, said end wall, and said plug between them defining a main chamber which has a first volume, - said plug has a central channel which prior to the priming of the cracking cartridge is closed by a sealing membrane, - a cracking powder charge, in a compressed state thereof, has a second volume, - said main part of the detonator sleeve which can be introduced into the cracking cartridge has a third volume, - said second and third volumes together correspond to said first volume, - said sealing membrane in said plug can be penetrated by the detonator as the nose portion of the detonator is pressed with force against the sealing membrane, and