An auxiliary cartridge (60) for use in rock breaking is disclosed which comprises an elongate body (62), an end closure (66, 90) at each end of the body (62) and a charge of combustible material in the space defined by the body (62) and the end closures (66, 90). The end closure (66) includes a frangible membrane (86) which closes off a charge (88) of combustible chemicals. On being subjected to the pressure of an external ignition of fast burning combustible material, the membrane (86) fails and permits flame to flash through it from externally of the auxiliary cartridge to internally thereof thereby to ignite said charge.
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