Minerals, basic component of rocks. Today: One Rock. Minerals. Common minerals Igneous + Metamorphic Rocks. Weathering Rocks Minerals Clays
Today: • Apply chemical, physical weathering
Minerals, basic component of rocks A naturally occuring inorganic (usually) material with certain physic...
One Rock • Churt - high in Si • Dolomite Ca and Mg carbonates • Sphalerite ZnS
Weathering Rocks Minerals Clays • Rocks get broken down into smaller and smaller pieces until the pieces consist of single minerals • These minerals small enough: silt and clay fraction
• Hornblende – Ca2Al 2Mg2Fe3Si6O22 (OH)2
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Weathering Rocks Minerals Clays
Physical Weathering (disintegration) • Result of Temperature
• Capacity to weather depends on basic mineral composition – Softer will break down faster – Higher Fe, Mg will break down faster
Physical Weathering • Different minerals within a solid will react differently to changes in temperature • Presence of water will accelerate process
Physical Weathering (disintegration) • Result of Water, Ice, and Wind
Chemical Weathering • Accelerated by: – Water – Oxygen – Organic and inorganic acids
Chemical Weathering (decomposition)
• All things that you don’t find in the mantle
• Oxidation
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Chemical Weathering • Hydration - + H2O • Solid + water = hydrated solid – Al2O3 + 3 H2O
Al2O3• 3 H2O
Chemical Weathering • Hydrolysis - H2O H+ + OH• Solid + water = solid + ion + OH– KAlSi3O8 + 11 H2O OH-
Carbonation = Acidification • Text calls weathering of rocks by H2CO3 (carbonic acid) carbonation • Process is one type of acidification
LEO - will occur in aerobic environment • 2FeS + 5H2O + 4.5 O2 + 2H2 SO4-
2Fe(OH)3
Chemical weathering of igneous and metamorphic rocks • Rocks higher in Fe and Mg will tend to weather faster • Will lose Fe and Mg in the process
• Fe in primary minerals is black • As Fe oxidized (weathers) it turns red like rust
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KAlSi3O8
Basic Trends
Type of feldspar • KAlSi3O8 + H20
HAlSi3O8 +K+ +OH-
• HAlSi3O8 + H20
Al2O3 +6H4SiO4
• Base forming cations (Mg, Ca, K) will tend to go into solution –Important source of plant nutrients
• Si will tend to form H4SiO4 –This is a soluble acid and will weather
• Al and Fe will tend to form oxide minerals
Rock to Soil Granite Element P Ca Si Fe
In Rock 0.057 1.07 32.9 2.5
In Soil 0.035 0.23 21.8 8.54
Weathering process %Change -38 -79 -34 +242
Older soils • Will have less soluble nutrients • Will have more Fe and Al oxides • Will have more ??? color
• Primary minerals Secondary minerals (including clays) • Generally associated with loss of Si, P, K, Mg… • Increase in prevalence of Fe and Al clays
Which mineral would you expect to form a fertile soil? • Quartz- SiO2 • Olivine - (Mg,Fe)2SiO4
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Where would you expect rocks to weather faster? Where would you expect rocks to weather faster?
Both sites (Alaska and Puerto Rico) are wet Higher temperatures in Puerto Rico will accelerate weathering process
Puerto Rico, Oxisol
Alaska, Gelisol
Where would you expect more rapid chemical weathering?
Where would you expect more rapid chemical weathering?
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Desert vs Tropical Rainforest • Temperature regime is similar • Water will accelerate weathering process • Physical weathering will be predominant mechanism in desert
Where would you expect expansion of water due to freezing to play a greater role in weathering?
Utah, Aridisol
Puerto Rico, Oxisol
Where would you expect expansion of water due to freezing to play a greater role in weathering?
Greenland vs Vermont • For freezing water to play an important role in weathering, it has to thaw as well • Freeze, thaw cycles accelerate weathering process
Alaska, Gelisol Vermont, Spodisol
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It may not seem like fun, but…. • What process is going on here? 3MgFeSiO4 + 2H2O H4Mg3Si2O9 + SiO2 + 3FeO • And here? 4FeO + O2 2Fe2O3
Nature of the parent material will greatly influence time it takes to make soil and the nature of the soil that is formed
Colluvial debris: Rocks that have fallen down hills
Weathered Rocks from the lithosphere are the parent materials for soils
Types of Parent Material • • • • • •
Residual Colluvial Water Ice Wind Organic material
Residual: Parent material in place
Woodson soil series, KS formed from sediment
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• Water:Alluvial deposits Sediment that is deposited by rivers
• Water:Alluvial deposits Sediment that is deposited by rivers
Water:Marine (sediments deposited by oceans)
Water:Lacustrine (materials deposited by lakes)
Glacial till: Material transported by glacial ice Pleistocene Epoch 2 million years
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Glacial till: Material transported by glacial ice
Paloose - eolian materials
Eolian: Materials transported by wind Loess
Eolian: Materials transported by wind
Volcanic ash
Organic:Wet areas where accumulation> decomposition Peat bogs
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(1)Parent materials + 4 other factors of soil formation • • • •