Rick's Cafe in Jamaica

Keith Fairbrother

Erosion Door County, WILizzy Schneider

Erosion Timna Valley, IsraelNaamah Azoulay

CHEMICAL WEATHERINGDISSOLUTION

Water removes ions or ion groups from a rock ormineral and carries them away.

Precipitate later when water evaporates.Due to the bipolar nature of water molecules,

ions become dissolved and are transported insolution.

WEATHERING and the BREAKDOWN of ROCKS

CHEMICAL WEATHERING

DISSOLUTION

HaliteNa+ is attracted to OH- side of water moleculesCl- 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 Ca+2 + 2HCO3- (Bicarbonate)

Removed by erosion

WEATHERING and the BREAKDOWN of ROCKS

Calcite

CHEMICAL WEATHERING

DISSOLUTION

Dissolution is the process by which caves are formed.Calcite is dissolved, Ca+2 and HCO3

- end up in theocean.

Then removed from the ocean by marine organismsin the production of skeletal material.

WEATHERING and the BREAKDOWN of ROCKS

CHEMICAL WEATHERING

OXIDATIONPositive 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

WEATHERING and the BREAKDOWN of ROCKS

Also affects other metals such as copper.

CHEMICAL WEATHERING

OXIDATION

WEATHERING and the BREAKDOWN of ROCKS

Oxidation has the same result with iron-rich rocksand minerals.

Affects olivine, pyroxenes, amphiboles, gabbrosand basalts.

CHEMICAL WEATHERING

HYDROLYSIS

WEATHERING and the BREAKDOWN of ROCKS

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

Al2Si2O5(OH)4 + 4H4SiO4 + 2K+

OrthoclaseFeldspar

Kaolinite SilicicAcid

Hydrolysis of orthoclase, other feldspars and maficminerals produces clays and clay minerals.

Clays become incorporated in soils or wash to thesea by erosion.

Dissolved materials produced can cement sedimentary grains

Or, be utilized by plants (K+).

CHEMICAL WEATHERING

HYDROLYSIS

WEATHERING and the BREAKDOWN of ROCKS

So……

What are the factors that influence

CHEMICAL WEATHERING?

FACTORS THAT INFLUENCE CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

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 increaseschemical weathering.

FACTORS THAT INFLUENCE CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

LIVING ORGANISMSMix up soil exposing more material to surface for

weathering reactions.

FACTORS THAT INFLUENCE CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

TIME

The longer a rock or mineral is exposed to weatheringthe more weathering takes place.

FACTORS THAT INFLUENCE CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

MINERAL COMPOSITION

The effect of chemical weathering in rocks is relatedto 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 thetetrahedra, the more resistant to weathering is the mineral.

WEATHERING and the BREAKDOWN of ROCKS

PRODUCTS OF CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

Or….What’s left after dissolution, oxidation andhydrolysis.

Clay Minerals Produced by hydration of feldspars and

mafic minerals (olivine, pyroxenes, andamphiboles).

PRODUCTS OF CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

CLAY MINERALSType 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 drillingBricks and cement Paper productionCat litter KaopectateFiltering impurities from beer and wine

PRODUCTS OF CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

METAL ORES

AluminumForms from chemical weathering of feldspar-

rich rocks in warm, humid climates.Leads to the concentration of aluminum in

Bauxite (Al2O3 . nH2O).

PRODUCTS OF CHEMICAL WEATHERING

WEATHERING and the BREAKDOWN of ROCKS

SPHERIODAL WEATHERING

Mechanical weathering breaks up rocks into smallerpieces.

Chemical weathering rounds off corners.

SOILS AND SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

Mechanical and chemical weathering of sedimentand pre-existing bedrock below producesREGOLITH.

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.

SOILS AND SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

REGOLITH

REGOLITH

SOILS AND SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

SOIL

SOIL

INFLUENCES ON SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

PARENT MATERIAL

The bedrock or sediment from which soil forms.Influences nutrient richness of the soil.

Quartz-rich sandstoneBasalt

INFLUENCES ON SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

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.

INFLUENCES ON SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

TOPOGRAPHY

Physical features of the landscape.Influences the availability of water.Influences the rate of soil accumulation.Steep slope vs. gentle slope

INFLUENCES ON SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

VEGETATION

Contributes organic matter to soil.Produces CO2 and O2 involved in chemical weathering.Plants contribute H+ that helps weather soils.

Aids in hydrolysisDegrades feldspars and other mineralsinto clay minerals.

Clays increase nutrient supply to plants.

INFLUENCES ON SOIL FORMATION

WEATHERING and the BREAKDOWN of ROCKS

TIME

The longer the time Earth materials are weathered, the thicker the soil produced.