A rail welding crucible and cap with burner-ignited reaction starter mix has a cap, an igniter core, and a crucible. The igniter core is a mixture of material that can be ignited by an oxygen/propane gas rail-preheating burner and forms the reaction starter mix for an aluminothermic reaction. The cap is mounted over the crucible and used to hold the igniter core in a desired position. A core-receiving hole traverses through the cap, from a first face to a second face. The igniter core is mounted within the core-receiving hole so that the igniter core can flow into a reaction cavity of the crucible. The reaction cavity is a receptacle within the crucible which serves as a temporary holder for a quantity of rail-bonding material that undergoes the aluminothermic reaction. The quantity of rail-bonding material becomes molten and flow onto the joint once the aluminothermic reaction reaches a desired phase.