GEO 101 Lecture Notes - Lecture 6: Thermal Expansion, Calcite, Hydrolysis
21 Feb 2018
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Sedimentary Rocks- rocks formed near or at the surface of the Earth
by cementing together loose grains that have been produced by:
• Physical or chemical weathering
o The physical breakdown and chemical alteration of rock
at Earth’s surface
o Types of Weathering:
▪ Physical (mechanical)- breakdown of pre-
existing rock
Breaking of rock into smaller pieces
How does this happen?
• Frost wedging- expansion of water in
cracks by freezing, wedging the rock
apart
• Unloading (pressure release)- as
pressure is decreased,
igneous/metamorphic rock expands
and fractures in large sheet-like layers
• Thermal expansion and contraction-
most common, rapid heating and
cooling of rocks surface, resulting in
expansion/contraction of the rocks
surface
• Biological activity- cracking and
expansion due to plant growth on top
of rocks
▪ Chemical- chemical reactions occur that change
the chemical composition of the rock
Dissolution- dissolving of the material (acid
rain)
Hydrolysis- incorporates water into the
mineral structure
Oxidation- formation of oxide (red soil in
Alabama- iron oxidizing)
▪ Both types of weathering happen
simultaneously!!!
o Factors effecting rates of weathering-
▪ Surface area- fractures of rock
Greater surface area=faster weathering
▪ Rock composition
Example- calcite dissolves in weak acid,
sinkholes!!
Felsic material is more resistant to
weathering than mafic
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