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The element iron combines with oxygen, producing relatively insoluble iron oxides,
which give soil a reddish-brown or yellowish color. Under most conditions the three
remaining elements— aluminum, silicon, and oxygen—join with water to produce
residual clay minerals. However, even the highly insoluble clay minerals are very
slowly removed by subsurface water.
Spheroidal Weathering. In addition to altering the internal structure of minerals,
chemical weathering causes physical changes. For instance, when angular rock masses
chemically weather as water enters along joints, they tend to take on a spherical shape.
Gradually the corners and edges of the angular blocks become more rounded. The
corners are attacked most readily because of their greater surface area, as compared to
the edges and faces. This process, called spheroidal weathering, gives the weathered
rock a more rounded or spherical shape.

Task 2. Answer the questions (in written form):
1. What products result when carbonic acid reacts with potassium feldspar?
2. What is spheroidal weathering?

Task 3. Read the text and translate it into Ukrainian (in written form).

D I D Y O U K N O W?
The moon has no atmosphere, no water, and no biological activity. Therefore,
the weathering processes we are familiar with on Earth are lacking on the Moon.
However, all lunar terrains are covered with a soil-like layer of gray debris, called lunar
regolith, derived from a few billion years of bombardment by meteorites. The rate of
change at the lunar surface is so slow that the footprints left by Apollo astronauts will
likely remain fresh-looking for millions of years.

Test yourself

Task 1. Tell whether the sentences are true or false. Correct the false ones.
1. Earth is a stable body.
2. Mountain building and volcanic activity are internal processes on Earth.
3. Weathering is the physical breakdown (disintegration) and chemical alteration
(decomposition) of rocks at or near Earth’s surface.
4. Erosion is the transfer of rock and soil downslope under the influence of gravity.
5. Transformation of rock due to a very different and comparatively hostile surface
environment is called weathering.
6. Chemical weathering is accomplished by physical forces that break rock into
smaller and smaller pieces without changing the rock’s mineral composition.
7. The process of expansion of water upon freezing leads to fracturing rocks in
nature.
8. Only chemical weathering is accomplished by the activities of organisms.
9. Quartz is not very resistant to chemical weathering.
10. Silicate minerals are composed essentially of only eight elements.
11. When granite weathers, the feldspar crystals turn to clay.
12. Water is the most important agent of chemical weathering.

Task 2. Choose the best variant of the answer:

Internal processes, mass wasting, external processes, erosion, weathering

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