Primary rocks are classified into three main types: igneous, sedimentary, and metamorphic. The antonyms for the word "primary rocks" would be secondary rocks or tertiary rocks. Secondary rocks are formed by various stages of weathering and erosion of pre-existing primary rocks, while tertiary rocks are formed due to deposition, alteration, and hardening of sediments.
Examples of secondary rocks include sandstone, shale, and limestone, which are formed from the erosion of primary rocks such as granite, basalt, and volcanic tuffs. Meanwhile, examples of tertiary rocks are gneiss, slate, and marble, which are formed due to intense pressure and heat applied to existing rocks over time.
Overall, while primary rocks are formed through initial geological processes, secondary and tertiary rocks are formed through subsequent weathering, erosion, and deposition processes.