In geology, what are the main classification for rocks?
There are three general classes of rocks: Igneous, Sedimentary, and Metamorphic.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: In geology, what are the main classification for rocks?
### Input: 
### Response: There are three general classes of rocks: Igneous, Sedimentary, and Metamorphic.