Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Many natural rock formations change color over time. In Utah, for example, iron oxidized and formed red, orange, and yellow rock. Which of the following is the cause of this change?
chemical weathering
Iron oxidation.