Download Metamorphism and Metamorphic Rocks

Rick's Cafe in Jamaica
Keith Fairbrother
Erosion Door County, WI
Lizzy Schneider
Erosion Timna Valley, Israel
Naamah Azoulay
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
DISSOLUTION
Water removes ions or ion groups from a rock or
mineral and carries them away.
Precipitate later when water evaporates.
Due to the bipolar nature of water molecules,
ions become dissolved and are transported in
solution.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
DISSOLUTION
Halite
Na+ is attracted to OH- side of water molecules
Cl- is attracted to the H+ side of water molecules
Water can also react with another compound to form an acid.
H2O + CO2
H2CO3 (Carbonic acid)
The acid can then decompose minerals.
H2CO3 + CaCO3
Calcite
Ca+2 + 2HCO3- (Bicarbonate)
Removed by erosion
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
DISSOLUTION
Dissolution is the process by which caves are formed.
Calcite is dissolved, Ca+2 and HCO3- end up in the
ocean.
Then removed from the ocean by marine organisms
in the production of skeletal material.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
OXIDATION
Positive ions in minerals combine with oxygen to
produce oxides.
4Fe+3 + 3O2
2Fe2O3
(hematite)
If the reaction takes place in water,
limonite (FeOOH) is produced.
Collectively called RUST.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
OXIDATION
Also affects other metals such as copper.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
OXIDATION
Oxidation has the same result with iron-rich rocks
and minerals.
Affects olivine, pyroxenes, amphiboles, gabbros
and basalts.
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
HYDROLYSIS
H+ and OH- ions in water displace other ions in a
mineral structure producing a new mineral.
Feldspars are readily changed by hydrolysis.
2KAlSi3O8 + 2H+ + 9H2O
Orthoclase
Feldspar
Al2Si2O5(OH)4 + 4H4SiO4 + 2K+
Kaolinite
Silicic
Acid
WEATHERING and the BREAKDOWN of ROCKS
CHEMICAL WEATHERING
HYDROLYSIS
Hydrolysis of orthoclase, other feldspars and mafic
minerals produces clays and clay minerals.
Clays become incorporated in soils or wash to the
sea by erosion.
Dissolved materials produced can cement
sedimentary grains
Or, be utilized by plants (K+).
So……
What are the factors that influence
CHEMICAL WEATHERING?
WEATHERING and the BREAKDOWN of ROCKS
FACTORS THAT INFLUENCE CHEMICAL WEATHERING
CLIMATE
Water drives all three reactions discussed.
Heat also speeds reactions.
Warm, humid climates are most suitable for chemical
weathering reactions.
Warm, humid climates also tend to have more plants.
When plants die, decomposition increases the
production of organic acids and increases
chemical weathering.
WEATHERING and the BREAKDOWN of ROCKS
FACTORS THAT INFLUENCE CHEMICAL WEATHERING
LIVING ORGANISMS
Mix up soil exposing more material to surface for
weathering reactions.
WEATHERING and the BREAKDOWN of ROCKS
FACTORS THAT INFLUENCE CHEMICAL WEATHERING
TIME
The longer a rock or mineral is exposed to weathering
the more weathering takes place.
WEATHERING and the BREAKDOWN of ROCKS
FACTORS THAT INFLUENCE CHEMICAL WEATHERING
MINERAL COMPOSITION
The effect of chemical weathering in rocks is related
to the stability of the minerals in the rock.
Since most rock-forming minerals are silicates, the
strength of the bonds between the silica
tetrahedra influences how they are weathered.
The more silicon-oxygen bonds between the
tetrahedra, the more resistant to weathering is
the mineral.
WEATHERING and the BREAKDOWN of ROCKS
WEATHERING and the BREAKDOWN of ROCKS
PRODUCTS OF CHEMICAL WEATHERING
Or….What’s left after dissolution, oxidation and
hydrolysis.
Clay Minerals
Produced by hydration of feldspars and
mafic minerals (olivine, pyroxenes, and
amphiboles).
WEATHERING and the BREAKDOWN of ROCKS
PRODUCTS OF CHEMICAL WEATHERING
CLAY MINERALS
Type of clay formed depends on climatic conditions
during hydrolysis.
Kaolinite forms in warm, humid climates.
Smectite forms in cool, dry climates.
Uses of clay minerals:
Agricultural fertilizers
Lubricants in oil drilling
Bricks and cement
Paper production
Cat litter
Kaopectate
Filtering impurities from beer and wine
WEATHERING and the BREAKDOWN of ROCKS
PRODUCTS OF CHEMICAL WEATHERING
METAL ORES
Aluminum
Forms from chemical weathering of feldsparrich rocks in warm, humid climates.
Leads to the concentration of aluminum in
Bauxite (Al2O3 . nH2O).
WEATHERING and the BREAKDOWN of ROCKS
PRODUCTS OF CHEMICAL WEATHERING
SPHERIODAL WEATHERING
Mechanical weathering breaks up rocks into smaller
pieces.
Chemical weathering rounds off
corners.
WEATHERING and the BREAKDOWN of ROCKS
SOILS AND SOIL FORMATION
Mechanical and chemical weathering of sediment
and pre-existing bedrock below produces
REGOLITH.
REGOLITH is all the material above the bedrock.
SOIL is the upper part (up to a few meters) of
regolith that supports plant life.
Soil contains both mineral and organic matter
(decaying vegetation).
Soil also contains air and water.
WEATHERING and the BREAKDOWN of ROCKS
SOILS AND SOIL FORMATION
REGOLITH
REGOLITH
WEATHERING and the BREAKDOWN of ROCKS
SOILS AND SOIL FORMATION
SOIL
SOIL
WEATHERING and the BREAKDOWN of ROCKS
INFLUENCES ON SOIL FORMATION
PARENT MATERIAL
The bedrock or sediment from which soil forms.
Influences nutrient richness of the soil.
Quartz-rich sandstone
Basalt
WEATHERING and the BREAKDOWN of ROCKS
INFLUENCES ON SOIL FORMATION
CLIMATE
Precipitation and temperature influence soil formation.
Influences the rate of chemical weathering.
Also influences plant growth.
Soil formation is most rapid in warm, moist climates.
WEATHERING and the BREAKDOWN of ROCKS
INFLUENCES ON SOIL FORMATION
TOPOGRAPHY
Physical features of the landscape.
Influences the availability of water.
Influences the rate of soil accumulation.
Steep slope vs. gentle slope
WEATHERING and the BREAKDOWN of ROCKS
INFLUENCES ON SOIL FORMATION
VEGETATION
Contributes organic matter to soil.
Produces CO2 and O2 involved in chemical weathering.
Plants contribute H+ that helps weather soils.
Aids in hydrolysis
Degrades feldspars and other minerals
into clay minerals.
Clays increase nutrient supply to plants.
WEATHERING and the BREAKDOWN of ROCKS
INFLUENCES ON SOIL FORMATION
TIME
The longer the time Earth materials are weathered,
the thicker the soil produced.