There are two main types of solid structures: crystalline and amorphous. Crystalline structures are orderly with atoms arranged in repeating patterns, while polycrystalline structures show some irregularity. Quick cooling results in small crystals and slow cooling produces large crystals. Amorphous structures have atoms arranged randomly without order, which gives them different properties than crystalline structures. Rubber has an amorphous structure where the long chain molecules can rotate and stretch reversibly, producing elastic behavior.