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Weathering
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49
Geology
Undergraduate 1
10/16/2010

Additional Geology Flashcards

 


 

Cards

Term

 

 

 

Weathering

Definition

- Changes that occur in rocks and minerals that are exposed to the atmosphere and surface conditions

 

- almost all rocks break down or decay either physically or chemically

Term

 

 

 

3 types of weathering

Definition

3 types of weathering:

 

1.)  Physical

2.)  Chemical

3.)  Biological

Term

 

 

 

Physical Weathering

(Mechanical Weathering)

Definition

Physical weathering - mechanical changes in rock whichbreak it down to smaller sizes without changing minerology

 

EX: Thermal

      Freeze/Thaw

      Salt crystal growth

      Jointing/Sheeting

 

- Physical weathering promotes chemical weathering

(Breaking rocks expose greater surface area)

Term

 

 

 

Thermal Physical Weathering

Definition

The expansion and contraction of minerals when they are heated (Expand) or cooled (shrink) in a rock

 - takes place in arid/semi arid regions

 

-Causes internal stress that can weaken the the cohesion between mineral grains resulting in breakage of the rock at its surface (exfoliation)

Term

 

 

 

Freeze/Thaw Physical Weathering

(Ice Wedging)

Definition

Freezing or thawing of water in pores and cracks

- water expands 9% of its original body when frozen

 

Repeated cycles of freezing and thawing can result in mechanical dissagregation of the rock

- Most effective where freezing and thawing take place frequently

Term

 

 

 

Salt Crystal Growth Physical Weathering

Definition

Salt crystals grow in the cracks of rocks and break them

Term

 

 

 

Jointing/Sheeting Physical weathering

Definition

When rocks that were compressed come up to the surface and crack due to loss of pressure

 

- is accomplished by brittle rupture and formation of very small spaces along penetrative fractures termed expansion joints.

Term

 

 

 

Chemical Weathering

Definition

Changes in mineralogy by reaction with the atmosphere and water

 

3 Types

1.  Dissolution- dissolve mineral

 

2.  Oxidation- reduction (Redox)- Minerals react to Oxygen (rusting)

 

3.  Hydration - Dehydration- putting water into/ taking water away

Term

 

 

 

Chemical Agents

Definition

* Oxygen

* Water

* Carbon dioxide (CO2)

        H2O + CO2 --> H2CO3  (Carbonic Acid- weak acid)

* Sulfur Dioxide (SO2)

        H2O + SO2 --> H2SO4   (Sulfuric Acid - Strong Acid)

 

* Also humic acids from reaction with decaying vegetation (Organic Acids)

Term

 

 

 

Dissolution Reactions

Definition

NaCl + H2O -->   Na+ +  Cl-  +  H2O

  -  Salt + Water -->  Na+ and Cl- ions in solution

 

CaCO3 + H2O -->  Ca+2 + H2CO3

  -  Calcite + Water -->  Ca ion + Carbonic Acid

 

2FeS2 + 7O2 + 2H2O --> 2Fe+2 + 4H2SO4

  -  Pyrite + Oxygen + Water --> Fe ion + Sulfuric Acid

Term

 

 

 

Hydration Reactions

Definition

CaSO4 + H2O --> CaSO4 * 2H2O

  -  Anhydrite + Water --> Gypsum

 

2KAlSi3O8 + 2H+ + H2O --> AlSi2O5(OH)4 + 2K+ + SiO2

  -  Orthoclase+Acidic Water -->Kaolinite(Clay)+stuff in solution

 

Fe2O3 + 4H20 --> 2Fe(OH)3 * H2O

  -  Hematite + Water --> Goethite

Term

 

 

 

Oxidation Reactions

Definition

4Fe + 3O2 --> 2Fe2O3

  -  Iron + Oxygen --> Hematite

 

4FeS2 + 8H2O + 15O2 --> 2Fe203 + 8H2SO4

 (ferrous)                            (Ferric)

 

4FeSiO3 + O2 + 2H2O --> 4FeO(OH) + SiO2

(Ferrous)                            (Ferric)

  -  SiO2= Quartz - relatively stable/insoluable undermost conditions

  - Silicate minerals will react to chemical weathering and release silica into solution

Term

 

 

 

Chemical Weathering of Marble column

Definition

Marble carving being dissolved by dissolution

 

Marble= Calcite

Term

 

 

 

Biological Weathering

Definition

Changes produced by the action of plant or animal action on rocks

 - changes may be chemical or physical

 

EXAMPLES:

- Burrowing

- Root Growth

- Ion exchange with roots

- plant secreated acid

Term




Algea Growth

(Biological Weathering)

Definition

Algae growth on rocks dissolve minreals to obtain nutrients

Term

 

 

 

Mineral Responses to Weathering

(Fe Bearing Silicates, Feldspar, Quartz, Muscovite Mica, Calcite)

Definition

Original Mineral                         Weathering Product

Fe bearing silicates                      Clay minerals

(olivine, pyroxene, Amphibole,           (Iron Oxides)

Biotite)          

 

Feldspar                                     Clay minerals

                                                 (K, Na, Ca ions)

 

Quartz                                        Quartz

 

Muscovite Mica                            Clay Minerals

                                                    (K ions)

 

Calcite                                        Ca, Co ions

Term

 

 

 

Feldspar

(Mineral Responses to Weathering)

Definition

Weathering Product

 

Clay Minerals

(K, Na, Ca ions)

Term

 

 

 

Quartz

(Mineral Responses to Weathering)

Definition

Weathering Product

 

Quartz

(Does not change)

Term

 

 

 

Muscovite Mica

(Mineral Responses to Weathering)

Definition

Weathering product

 

Clay Minerals

(K ions)

Term

 

 

 

Calcite

(Mineral Responses to Weathering)

Definition

Weathering Product

 

Ca, CO ions

Term




Granite

(Rock Responses to Weathering)

Definition

Granite --> Quartz, Clay, Minor Fe Oxide

  -  K-Spar, maybe biotite

Term

 

 

 

Diorite

(Rock Responses to Weathering)

Definition

Diorite --> Fe Oxides, Clays, +/- Quartz

Term

 

 

 

Gabbro

(Rock Responses to Weathering)

Definition

Gabbro --> Fe Oxides, Clay

  -  Lots of dark minerals

Term

 

 

 

Slate

(Rock Responses to Weathering)

Definition

Slate --> Chemically stable, mechanically weak

  -  Metamorphic (clays = baked)

          -  not very strong

Term

 

 

 

Limestone

(Rock Responses to Weathering)

Definition

Limestone --> Dissolves (residual insol.)

- will weather away

Term

 

 

 

Sandstone

(Rock Responses to Weathering)

Definition

Sandstone --> Quartz unchanged

  -  stability depends on what holds it togethor


- Cements affected accordingly to solubility

      Silica Stable

      Fe Oxide Stable

      Calcite Soluable

Term

 

 

 

Goldrich Stability Series

Definition

(Most susceptible to weathering)

Olivine                                                    Ca-rich

          Pyroxene                                  Plagioclase

                  Amphibole

                        Biotite         Na-rich

                                       plagioclase

K-spar

Muscovite

Quartz

(Least Susceptible to weathering)

 

Quartz/K-spar are most stable

Term

 

 

 

Typical Climate Conditions

Definition

Polar- to cold to hold moisture

 

Tropic- hot and wet

 

Temperate- Warm (not super cold) with moderate rain

 

Arid- Very Dry

Term

 

 

 

Cleopatra's Needle

Definition

Desert -> Humid

Result from weathering

Term

 

 

 

Soils

Definition

Surface mantle of rock weathering products that support life ( microbes to trees and elephants)

 

Engineer's definition - surface mantle that can be excavated without blasting

 

Soils are important as:

1.  source materials of sediments

2.  layer in which plants grow

Term

 

 

 

Residual Soils

Definition

Soils formed where they are found (formed in place)

 

Soil development is controlled by:

1. Time (the more time, the more soil erodes)

2. Slope (the materials wash out and get carried away)

3. Climate (controlls how long it takes for soil to erode)

4. Parent rock

5. Vegetation and Organisms

Term

 

 

 

Ideal Soil

(Horizons)

Definition

O horizon - organic, alot of dying/dead plant material (black soil) may not be present. 0-2'

 

A horizon - Same organic material is in it, alot of quartz grains, catalyst mineral stuff, contains humus leached zone. 2-10'

 

B horizon- Brown, no organic material, rich in clays, brown to red, enriched in clay and/or Fe oxides. 10-30'

 

C horizon- Transition zone, bed rocks and pieces of bed rock, partially weathered out materials, light yellow brown. 30-48'

Term

 

 

Additional Horizons

(not always present)

Definition

E Horizon- Only present in acidic soils (pine forest) usually white

 

K Horizon- Only present in arid soils, zone of caliche

Term

 

 

 

Transported soils

Definition

Soils that result from deposition of weathered materials delivered from elsewhere

 

-  Many of the early agricultural centers were located on the flood plains and delta of major rivers. New soil is deposited with each flood

Term

 

 

 

Polar and Subpolar

(Soils and Climates)

Definition

slight weathering; thin, rocky soils, low temp, cold all the time

Term

 

 

 

Temperate

(Soils and Climates)

Definition

Moderate physical and chemical weathering; well developed pedalfers

Term

 

 

 

Tropical

(Soils and Climates)

Definition

Strong Chemical weathering; clays removed; only Al and Fe oxides and hydroxides stable-- Laterites

Term

 

 

 

Arid

(Soils and Climates)

Definition

weak chemical weathering, K horizon developed (Caliche) -- Pedocals

-  thin A and B horizons

Term

 

 

 

Sheeting

Definition

When expansion joints segment bedrock exposures into numerous parrallel rock layers often reffered to as sheets

 

Caused by Unloading or

Term

 

 

 

Pedalfer soil

Definition

Form in temperate climates where there is sufficient precipitation to flush out most soluable products of chemical weathering

- Rich in aluminum and iron and are generally fertile

Term

 

 

 

Pedocal Soil

Definition

From in arid/sem-arid environments if there is insufficient precipitation to completely wash out soluable weathering products

 

- Typically precipitate within the B-Horizon and accumulate to form deposits termed caliche or hard-pan

Term

 

 

 

Laterite Soil

Definition

Form in tropical and sub-tropical climates where chemically weathering is so extensive and precipitation so frequent that only the most insoluable elements remain

 

- Infertile and represented by bauxite the principle ore for aluminum

Term

Iron Oxide are common at the surface of the earth because it forms by the weathering of....

 

A.  Dark Minerals of Bowen's Reaction Series

B.  Clay Minerals

C.  Feldspar

D.  Shale

Definition
A. Dark Minerals of Bowen's Reaction Series
Term

Which of the following is most susceptible to chemical weathering by dissolution?

 

A.  Calcite

B.  Hematite

C.  Clay Minerals

D.  Quartz

Definition
A.  Calcite
Term

Which of the following is most likely to dissolve away in semi-humid environments?

 

A.  Calcite

B.  Gypsum

C.  Aluminum Oxide

D.  Clay Minerals

Definition
B.     GYpsum
Term

Feldspars Weather to...

 

A.  Iron Oxide

B.  Calcium Carbonate

C.  Quartz

D.  Clay

Definition
D.  CLay
Term

In which region of the USA are pedalfers most likely to form?

 

A.  Southwest USA

B.  Southeast USA

C.  Extreme Northeast

D.  Utah

Definition
B.     Southeast USA
Term

Pedocal soils have a thick...

 

A.  A horizon

B.  B horizon

C.  Caliche layer

D.  E horizon

Definition
C.     Caliche layer
Term

A buried B-Horizon may eventually be preserved as a very thin...

 

A.  Shale

B.  Sandstone

C.  Limestone

D.  Coal

Definition
A.     SHale
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