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SOIL 4400 > Soil Minerals > Flashcards

Soil Minerals Flashcards

1
Q

What are two typical structural components of minerals?

A
  1. Silicon (Si) tetrahedral
  2. Aluminum (Al) octahedral
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2
Q

What is the structure and charges on Silicon tetrahedral?

A

One Silicone in the middle with a charge of +4 surrounded by 4 Oxygens. Each with a charge of -2 making the net charge -4.

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3
Q

How does the number of oxygens shared by silicone tetrahedrals alter the structure?

A

If silicone tetrahedrals share one or two oxygens, they have a chain structure. If three oxygens are shared, they have a sheet structure, and if all four oxygens are shared, they have a framework structure.

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4
Q

What does the increased sharing of O2 lead to?

A
  1. ↑ in Si/O ratio
  2. Chain, sheet, or framework structure depending on the # of oxygens shared.
  3. ↓ surface area, ↓ adsorption, ↑ stability, ↓ weathering
  4. ↓ negative charge, ↓ surface charge, and # of ‘ accessory’ cations between tetrahedral
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5
Q

Why does the adsorption of accessory cations decrease as the number of shared oxygens increase?

A

because the charge is closer to net 0 and it is harder for cations to be attracted to that.

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6
Q

What are the 2 types of minerals?

A
  1. Primary minerals
  2. Secondary minerals
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7
Q

What are 3 characteristics of primary minerals?

A
  1. Chemically unchanged from igneous rocks.
  2. Original source for most mineral nutrients
  3. Mainly silicates.
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8
Q

What are the three important primary minerals?

A
  1. Quartz
  2. Feldspars
  3. Micas
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9
Q

What are the 5 characteristics of quartz?

A
  1. Pure silicates
  2. Silicate tetrahedral in framework structure
  3. Vey resistant to weathering.
  4. No nutrients in bulked solid or adsorbed on the surface.
  5. Abundant in sand and silt in most soils.
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10
Q

What are some characteristics of feldspars?

A
  1. framework structure
  2. Less stable than quartz
  3. Abundant in sand and silt of temperate regions
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11
Q

What are some characteristic of micas?

A
  1. An example of a layer or phyllo silicate.
  2. Al silicate with one aluminum octahedral sandwiched between 2 silicate tetrahedrals.
  3. resistant to weathering
  4. Isomorphous substitution of Al 3+ for Si 4+. Offset by K + held tightly between the layers.
  5. Important source of K+
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12
Q

What are three characteristics of secondary minerals?

A
  1. Product of weathering of primary minerals
  2. Abundant in clay
  3. Contribute to Cation Exchange Capacity
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13
Q

What is isomorphous substitution?

A

Ions of similar size are substituted during formation. For example Al 3+ for Si 4+ or Fe2+ for Al 3+. This results in a net negative charge that affects interlayer bonding.

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14
Q

What is the ratio for Si-t: Al-o for Kaolinite?

A

1:1

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15
Q

What is the ratio for Si-t: Al-o for Mica?

A

2:1

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16
Q

What is the ratio for Si-t: Al-o for Smectite?

17
Q

What is the ratio for Si-t: Al-o for Vermiculite?

18
Q

What are some characteristics of Kaolinite?

A

Little isomorphous substitution aka ionic substitution. Low CEC, high stability, and non-expansive.

19
Q

What are some characteristics of Mica/illite?

A

Lots of isomorphous substitutions, mostly Al 3+ for Si 4+ in tetrahedral sheets. Medium CEC. Long term slow release of K+

20
Q

What are some characteristics of Vermiculite?

A

Isomorphous substitutions give high neg charge in Si-T sheet. Expands during wetting. High CEC.

21
Q

What are some characteristics of Smectite?

A

Most isomorphic substitutions in the Al-octahedral sheet. Attraction between layers is weak water and any hydrated cations enter interlayer space. Large expansion upon wetting. High CEC.

22
Q

What are some effects of soil minerals on soil ecology?

A
  1. They help with the formation of aggregates by bonding together soil particles.
  2. Provide a supply of nutrients for SOM.
  3. Release acids and bases for soil ph.
23
Q

What effect does weathering have on soil ecology?

A

Weathering of solids releases nutrients and acidifies soil.

24
Q

What factors increase weathering?

A
  1. ↓ Oxygen sharing (framework, sheet, chain, isolated)
  2. ↓ Particle size (clay breaks down easier than sand)
  3. ↑ Temp.
  4. ↑ Moisture
25
Q

What are the two types of negative charges for cation exchange?

A
  1. Permanent
  2. Variable (pH dependent)
26
Q

What is an example of a permanent charge?

A

Isomorphous substitution. Ex: Al 3+ for Si 4+. This results in a ↑ neg. charge independent of pH. It is also main source of CEC in 2:1 silicates.

27
Q

What is the main source of CEC for 1:1 substitution?

A

Variable charge

28
Q

How does the removal of H+ affect soil?

A
  1. ↑ neg. charge
  2. ↑ CEC
  3. ↑ pH.
29
Q

What is it called when the decrease in pH can change the charge from + to -?

A

Amphoterism

SOIL 4400 (8 decks)

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