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Soils- Clay > Clays > Flashcards

Clays Flashcards

1
Q

What are the 3 most common elements in the Earth’s crust and in what %?

A
  1. Oxygen 49.2%
  2. Silicon 25.7%
  3. Aluminum 7.5%
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2
Q

What elements are required to produce silicates?

A

O, Si, Al, Fe, Ca, Na, K, Mg

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3
Q

What are the 6 silicate RFM?

A
  • Olivine
  • Hornblende
  • Augite
  • Micas
  • Feldspares
  • Quartz
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4
Q

Where does clay come from?

A
  1. Silicate RFM form igneous rocks

2. Weathering of RFM producing CLAY minerals, nutrients, quarts and silts

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5
Q

Why is clay important?

A
  • significant component in soil
  • contributes up to 40% in sedimentary rocks
  • stores nutrients
  • contributes to development of soil structure
  • soil moisture holding capasity
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6
Q

What is the chemical structure of the silica tetrahedron?

A

SiO4 4-

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7
Q

What part of the clay is responsible for the negative charge?

A

3 of the 4 O atoms are bonding with other Si atoms so the negative charge only comes from the O on the edge of the sheet…. the internal atoms are neutralized

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8
Q

What is a clay crystal composed of?

A

2 connecting tetrahedrons (8 O and 2 Si) but 3 O are shared leaving 5 unbonded.

The formula is then: Si2O5 -2

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9
Q

6 silica tetrahedrons come together and for a ring. What is the chemical formula and what is found in the middle?

A

Si2O5(OH)-3

In the middle is a hydroxyl (OH-)

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10
Q

Concept:
O from silica tetrahedrons can bond with Al, Mg or Fe to form the 8 sided octahedron.

So now there is a bonded tetrahedron and octahedron

A

-

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11
Q

What is another word for clay microcell?

A

Micelles

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12
Q

What are the 2 most common clay patterns?

How are they arranged?

A

1: 1 and 2:1 and less common 2:1:1
1: 1 = 1 tetra and 1 oct
2: 1 = 1 oct sandwiched between 2 tetra

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13
Q

What are the 4 most common clay groups found?

A

Kaolinite
Smectite
Vermiculite
Chlorite

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14
Q

What are the clay microcell properties?

A
  • clay has a huge internal surface area

- the microcell has a net negative charge with capasity to attract cations

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15
Q

What are the more communications found in our region?

A 
H +
Ca2 +
Al3 +
Mg2 +
K +
Na +
and lesser NH4 +
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16
Q

What is the cationExchange Capacity? (CEC)

A

a measurement of the negative charge per unit mass of soil
or
soils ability to hold bases in the adsorption layer

17
Q

Are compounds tightly held in clay’s crystal lattice available for plant uptake?

A

NO

18
Q

Where are the available nutrients held?

A

Loosely held or adsorbed on the outer portion of the clay microcells —-> this is called the Defused double layer

19
Q

How is the CEC measured?

What is measured?

A

In milligram equivalents (meq) of hydrogen

H + is measured

20
Q

If all the exchange sites in 100g of soil could be occupied by 1 milligram of H+, then the soil would have _____ CEC or _____ meq, or _____ of hydrogen.

A

would have __1__ CEC or __1__ meq, or __1 milligram__ of hydrogen.

All the cations on the exchangeable cation exchange sites are replaced with the equivalent number of H+ ions

21
Q

How does the CEC range of clay differ from the range of OM?

A 
Clay = 0.4-0.5 meq/gram
OM = 2.5-4.0 meq/gram ( higher because the SA of OM is so much greater then clay)
22
Q

CEC associated with OM is highly dependent on what?

A

pH

high pH high CEC

23
Q

What is the Percent Base Saturation?

A

The mount of bases held on the cation exchange site

24
Q

What are the main anions of soil?

A

SO4 -2
borate B(OH)4 -
ammonia NO3 -
Phosphates H2PO4 -

25
Q

How are bases held in the clay complex?

A

Cation bridging

26
Q

What is soil reaction?

A

Another way of referring to soil pH and the effects of pH

27
Q

Why is soil pH so important?

A

Storage of nutrients and elements

28
Q

Why is clay referred to as “clay minerals”?

A

b/c it is a secondary mineral

29
Q

Where does clay come from?

A

Chemical weathering of silicates

30
Q

What is isomorphic substitution?

A

When Si is replaced with another element… this increases the net negative charge

31
Q

What limits # of nutrient holding sites on clays?

A

Size and Isomorphic substitution

32
Q

What are the factors that allow for Isomorphic substitution?

A

Atomic radius (function of the sub-atomic particles) and the valance

33
Q

What is the difference between the diffuse layer and the secondary diffused layer?

A

Diffuse layer = there the cations are located

Secondary Diffuse Layer = where anions are found

34
Q

The amount of cations soil can hold if a function of:

A

the amount of clay and the type of clay

35
Q

What dictates the # of nutrients present in soil?

A

the humus fraction and the clay fraction

36
Q

How does clay help with soil structure development?

A

(development of PEDs) acts as a binding agent!

37
Q

What is expansive clay?

A

clay prone to large volume changes that are directly related to water content.

Soils- Clay (1 decks)

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