The Two Main Types of Weathering: Physical vs. Chemical

By Jon Zamboni – Updated Aug 30, 2022

Weathering refers to the natural processes that break down and weaken earth’s minerals. Over time, these processes can strip away vast amounts of rock, reshaping landscapes and influencing erosion.

Physical Weathering

Physical, or mechanical, weathering erodes rock without changing its chemical composition. It involves the physical breakdown of stone through mechanisms such as fracture, abrasion, and thermal expansion.

• Wedging: When water freezes, salt crystallizes, or plant roots grow into cracks, the expansion forces the rock to split apart.
• Exfoliation: Rocks formed under high pressure are released at the surface; the loss of pressure causes outer layers to peel off in sheet‑like fragments.
• Abrasion: Wind or water carries sand and grit that grind against larger rocks, gradually wearing them smooth.

Chemical Weathering

Chemical weathering alters the mineral composition of rocks, making them weaker and more susceptible to physical breakdown. It involves reactions with water, oxygen, acids, and other substances in the environment.

• Oxidation: Exposure to air turns iron in minerals into rust (iron oxide), softening the rock.
• Hydrolysis: Water infiltrates minerals, reducing their density and strength—seen in the dissolution of gypsum.
• Acidification: Acids such as carbonic or nitric acid react with minerals, notably calcium in limestone and marble, leading to dissolution and damage—an effect amplified by acid rain.

Both physical and chemical weathering work in tandem, accelerating the breakdown of rocks and influencing soil formation, sediment transport, and the long‑term evolution of the planet’s surface.