Geology Reference
In-Depth Information
time becomes faded, scratched, chipped, or rusted. These changes are the result of
weathering, just like rocks experience.
When rocks are weathered, they change shape and sometimes composition.
Weathering changes the parent rock in one of two ways: by breaking it into smal-
ler particles called
sediments
or by changing its mineral composition through ion
exchange (see Chapter 5). I explain these different weathering processes here.
Mechanical weathering
Mechanical weathering
(also called
physical weathering
) changes the shape and size of a
rock, breaking it down into smaller pieces without changing its chemical composition.
Through mechanical weathering, rocks are broken down into sediment particles. This
process is illustrated in Figure 7-6.
Figure 7-6:
Mech-
anical weather-ing
of a rock into sedi-
ment.
There are four common types of mechanical weathering:
Frost wedging:
This type of weathering is most common in mountainous regions
and occurs when water seeps into cracks in a rock and freezes — expanding and
