Exfoliation is a form of _________.

Correct — C. Exfoliation is the peeling away of curved sheets or scales from a rock surface.

It breaks the rock apart without changing its mineral composition, and that is the test for physical or mechanical weathering.

The usual causes are pressure release as overlying rock is stripped off, and repeated heating and cooling of the outer skin. Option (c) is the family it belongs to.

Why the others are wrong

• (a)
  chemical weathering — Chemical weathering converts minerals into new substances through hydrolysis, oxidation, carbonation or solution. Exfoliation leaves the mineralogy untouched.
• (b)
  biochemical weathering — Biochemical weathering works through organisms and their acids, such as lichens and roots. No organism is needed for a granite dome to shed sheets.
• (d)
  mass wasting — Mass wasting is the downslope movement of already loosened material under gravity. It transports debris rather than producing it.

Weathering is the breakdown of rock in place, and it splits three ways.

Physical or mechanical weathering disintegrates rock without altering its chemistry, through frost wedging, salt crystallisation, thermal expansion, unloading and exfoliation.

Chemical weathering decomposes minerals into new substances using water, oxygen and acids.

Biological weathering works through living things and often acts chemically as well as physically.

Exfoliation is the classic unloading case. A granite mass loses its cover, the confining pressure falls, the rock expands and cracks parallel to the surface, and domes and sheet joints result.

Key facts

• Exfoliation is a physical weathering process in which sheets of rock peel off parallel to the surface.
• Unloading or pressure release is the main cause of exfoliation domes in granite.
• Weathering breaks rock in situ while mass wasting moves material downslope under gravity.

Common traps

• Choosing mass wasting because both processes involve rock coming away from a slope.
• Calling exfoliation chemical because heat and moisture are involved in the setting.

No directly related past PYQ was found.