The breakdown of rocks is caused by weathering and erosion and it can be classified as mechanical (or physical) and chemical weathering. Oxygen participates in the process of weathering as water (which is a product of oxygen and hydrogen). Water causes ice wedging in the cracks of rocks (expansion of water when it converts to ice) and also results in erosion of rocks. Oxygen directly participates in the chemical weathering of rocks through the process of oxidation. In this process, oxygen reacts with a substance within the rock and forms oxides which will result in weathering. The most common example of chemical weathering through oxidation is the rusting of iron. Any rock containing iron or iron minerals undergoes a slow breakdown this way. The resulting product is typically iron (III) oxide.
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