Final answer:
Geologists classify rocks into three types based on their origin: igneous from cooled magma or lava, sedimentary from cemented rock fragments, and metamorphic from transformed pre-existing rocks.
Step-by-step explanation:
Geologists recognize three main types of rocks based on their formation processes: igneous, sedimentary, and metamorphic. Igneous rocks form from the cooling and solidification of magma or lava, with minerals crystallizing and interlocking as the magma cools. Sedimentary rocks, on the other hand, are formed from weathered rock fragments or mineral precipitates that are cemented together. Lastly, metamorphic rocks are created when pre-existing rocks undergo transformation due to heat and pressure, which can cause foliation, a form of mineral patterning.