2.4. (9/2) Clay minerals, saprolite, and soils (Origin of sediments) Flashcards
What are the chemical ways to erode a rock?
- rainwater dissolves
List a sand factory
Biota
Soil
Saprolite
Core stones
Weathering front
Solid rock
Which acid does water and carbon dioxide make?
carbonic acid H2CO3
What kind of acid is H2CO3?
a simple, weak one
Is rainwater pH neutral?
no, it is weakly acidic (pH 5)
What is pH?
- A measure of how basic or acidic a solution is
- it is taking the negative log of the concentration of hydrogen ions -log(H+)
How do we know something is acidic? basic? neutral?
acidic: low pH
basic: high pH
neutral: 7
Which pH has more hydrogen ions?
acidic
what kind of relationship does pH have with hydrogen ions?
inverse
what kind of scale does pH have?
log scale at a factor of 10
What is the pH of carbonic acid?
A little under 5
Why is rainwater acidic?
Because it interacts with carbon dioxide
What are organisms doing to the organic material in the soil?
roots, fungi, and microbial communities are decomposing organic material in the soil
Which gas is released as a function of decomposition? how?
carbon dioxide through respiration
What are soils high in?
pCO2 environment
what does the p stand for in pCO2?
partial pressure of carbon dioxide gas
What is the parts per million of CO2 in the atmosphere?
about 420 ppm (partial pressure)
What is the partial pressure of CO2 in the soil?
10^4 - 10^5 ppm
What happens in the soil when it rains?
- when rainwater soaks into the soil, it picks up many more hydrogen ions
- soil water is more acidic than rainwater
Why might there be a big thick soil in one area but not another
positive feedback
What is critical to weathering reactions?
making a weak acid: carbon dioxide, hydrogen ions, and water
What is pyroxene?
a silicate
What kind of reactions are these:
1. CaSiO3 (wollastonite (silicate)) + 2Co2 + H2O -> Ca(2+) + SiO2 (aq) (silica) + 2HCO3(-)
2. CaCO3 (calcite (limestone, chemical sediment)) +CO2 +H2O -> Ca (2+) + 2HCO3 (-) (bicarbonate)
congruent dissolutions
What is congruent dissolution?
You pull a mineral apart and do not make another solid
Where do dissolution reactions occur?
soil to weathering front
where does the initial dissolution attack occur?
weathering front
What kind of reaction is this: 2FeO4 (magnetite Fe(2+)) + 1/2O2 + 4HCO3(-) + 4H(+) -> 3Fe2O3 (hematite Fe(3+) + 4H2CO3
oxidization (redox)
What is an example of an incongruent reaction?
Hydrolysis
What is an incongruent reaction?
hydrogen ion in aqueous solution (acid) that dissolves some of a mineral and creates a new mineral
What kind of reaction is this:
2KALSi3O8 (orthoclase feldspar) +2H(+) + 9H2O <-> H4Al2Si2O9 (kaolinite clay) + 4H4SiO4 + 2K(+)
Hydrolysis
How is gibbsite made?
By adding acid to kaolinite clay
What kind of reaction is this: H4Al2Si2O9 (kaolinite clay) + H(+) + H2O <-> 2Al(OH3) + 4H4SiO2
Hydrolysis (not balanced)
What is CaSiO3?
wollastonite (silicate)
What is 2HCO3(-)
bicarbonate
What is SiO2?
dissolved silicon dioxide
What is CaCo3?
limestone, chemical sediment (calcite)
What is H2CO3?
carbonic acid
What is 2Fe3O4?
Magnetite Fe(2+)
What is Fe2O3?
Hematite Fe(3+)
What is KAlSi3O8?
Orthoclase feldspar
What is H4Al2Si2O9?
Kaolinite clay
What is H4SiO4?
silica
What is Al(OH3)?
Gibbsite
What is a reduction?
gain of electron
what is oxidation
loss of electron
What is chelation?
the action of organic acids moving metals through soil with bonds
What is EDTA?
Ethylenediaminetetraacetic acid
What produces EDTA
plants, roots, fungi
What kind of reaction is this:
chelation
