Why do some rocks have lines and others don't?

Rocks have lines, or foliation, due to the alignment of mineral grains under pressure and temperature during their formation, often in metamorphic rocks. These lines indicate the directional stress the rocks experienced. In contrast, igneous and sedimentary rocks may lack such features because they formed through different processes, such as cooling from molten lava or the accumulation of sediments, which do not involve significant pressure or directional stress.