Peperite is a special kind of volcaniclastic rock formed by the intermingling of magma with wet sediments. The formation of peperite is mainly controlled by the fuel-coolant interactions (FCI) or phreatomagmatism and the fluidization of the host sediments. Peperite usually occurs at the bottom and the frontal part of the lava flows and is also distributed around shallow intrusions. Based on the textures, the authors classified peperite in northwestern Hebei into two types, i.e., fluidal and blocky. The fluidal peperite is produced by the mingling of magma with fine sediments, while the blocky peperite is related to coarse sediments. Correct identification of the peperite is important in studying the chronology of magmatism and the evolution of basins.