Page 113 - Science Course 2 (Book 2)

Mo10-L5a: What are Physical and Chemical Weathering?

Sediment is the material formed from rocks broken When water in a rock freezes, the expanding ice can
down by weathering. shatter the rock.

Sediment can be rock fragments, sand, silt, or clay. The force from the growing roots of plants can pry
open rock.

Wentworth Scale of Rock Particles Sizes

Classif cation Particle Size(diameter)

Boulder Above 256 mm

Cobble 64-256 mm

Pebble 4-64 mm Some minerals can react with water, air, or substanc-
es in water and air, such as carbon dioxide (CO2).
Gravel(or Granule) 2-4 mm
Chemical weathering is the process that changes
Very coarse sand 1-2 mm the composition of rocks.

Coarse sand 0.5-1mm Some minerals can dissolve in slightly acidic water,
such as rainwater.
Medium sand 0.25-0.5 mm

Fine sand 0.125-0.25 mm

Very f ne sand 0.062-0.125 mm

Silt 0.004-0.062 mm

Clay Less than 0.004 mm

Physical weathering is the process of breaking down
rock without changing the composition of the rock.

Physical weathering can occur because of forces
from plate motion, rupturing faults, and changes in Other minerals
weather. react with air and
water to form new
minerals.

Chemical
weathering
and physical
weathering
affect each other.

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