What is the difference between physical and chemical weathering?

Ask whether the minerals themselves have changed. If rock breaks into smaller fragments but its minerals’ chemical makeup stays the same, that is physical weathering. If at least some minerals are changed or dissolved, that is chemical weathering. The National Park Service describes freezing water expanding in cracks as physical weathering, and water dissolving mineral compounds as chemical weathering. [S1]

Here’s a compact comparison:

• Physical weathering: Rock breaks into pieces without changing the chemical makeup of its individual minerals. For example, water freezing and expanding in a crack can help enlarge it.
• Chemical weathering: At least some minerals change or dissolve. For example, slightly acidic water can react with minerals that bind sandstone grains.

These are examples, not rules that every rock weathers in exactly the same way. [S1][S2]

Not necessarily. The key distinction is movement: weathering breaks down or alters rock in place, while erosion is the removal or transport of the resulting material. A crack growing while the rock remains where it is is weathering. Once a fragment is carried away, that movement is erosion. The National Park Service uses this distinction in a sandstone example: freezing enlarges a crack through physical weathering, and the detached fragment is then eroded. [S1][S2]

A simple sequence is:

1. Water enters a crack in rock.
2. Freezing and expansion enlarge the crack: physical weathering.
3. A fragment breaks off but remains nearby: weathered material.
4. Wind or flowing water carries it elsewhere: erosion.

The exact agent and sequence depend on the example; the important point is that weathering itself does not include sediment movement. [S1]

Yes. The two processes are not mutually exclusive, and they can work together on the same rock. [S1] For sandstone, the National Park Service describes two pathways: repeated freezing can enlarge cracks while the rock remains sandstone; separately, slightly acidic rainwater can react with calcium carbonate that binds grains, releasing them. Wind or rain can then remove loosened material through erosion. [S2]

A worked explanation for a class discussion is:

“Freezing can widen a crack in sandstone without changing the minerals’ chemical makeup, so that is physical weathering. Slightly acidic water can also react with a mineral binder and release sand grains, which is chemical weathering. If wind or water later carries away a fragment or those grains, that movement is erosion.” [S1][S2]

This is an educational sandstone example, not a claim that all sandstone has the same binder or responds identically. The examples show the processes and their possible sequence; they do not predict how quickly a particular rock will weather. [S2]

Use these questions in order:

1. Is the rock being broken down or altered where it is? If not, you may be looking at transport rather than weathering.
2. Are its minerals’ chemical makeup unchanged as it breaks? If yes, classify the breakdown as physical weathering.
3. Are minerals changed or dissolved? If yes, classify it as chemical weathering.
4. Could both processes be involved? Say so when the example supports both.
5. Does a fragment or grain get carried away? Identify that movement as erosion, after the weathering.

When an example lacks enough detail to tell whether minerals changed, describe what is observable and say that the information does not establish the weathering type. Avoid guessing from the word “crack” or from the fact that sediment appears; explain the process evidence instead.