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Topic 9
Regents Earth Science
The break down of
rock material as a
result of chemical
and/or physical
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Physical weathering aka
mechanical weathering
 The
breakdown of rock into smaller
pieces without chemical change
1. Frost action
Weathering of rock
by the alternate
freezing and
thawing of water in
the pores or cracks
in the rock
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2. Plant action
Occurs when cracks in rock are widened
by the forces exerted by growing plants
Plant Action
3. Pressure unloading
 Occurs
when rocks split along the
planes of weakness when the pressure
of overlying material is removed
 Usually occurs as the result of natural
processes such as landslides, erosion,
and earthquakes
 But humans also cause this through
quarrying and mining
4. Abrasion
 The
physical action of scraping,
rubbing, grinding, or wearing away of
rock surfaces due to the movement of
solid sediment in an erosional system
such as stream or wind
*As time increases, particles
become more rounded.*
5. Exfoliation
 The
scaling or peeling of successive
shells from the surface of rocks
 Generally occurs in coarse-grained
rocks that contain feldspar (like granite)
Pressure Unloading and
Chemical weathering aka
 The
breakdown of rock by chemical
action, during which there is a change in
chemical composition of the minerals in
the rock
The agents of chemical
weathering include
1. oxygen
 The
chemical reaction of oxygen with
another element is called oxidation
2. water
 Speeds
up chemical reactions
 Dissolves many materials
 Reacts directly with many mineral
substances (hydrolysis)
Caves form
3. Carbon dioxide
 Easily
dissolves in water to form
carbonic acid
 Calcite, limestone, and marble react
with carbonic acid
 Reaction of carbonic acid with other
substances is known as carbonation
4. acids
 Produced
in the atmosphere by
lightning and on the surface by decay of
organic wastes
 Also gases released by people and
industry combine with water to form