SS105 2:1 Clays with Serious Charge

Are 2:1 layers slowly and carefully assembled under biosphere temperatures and pressures?

NO

How are 2:! layers formed?

Hastily thrown together while cooling atoms are frantically looking for oppositely charged pairs.

In 2:1 clays, is there substitution or is there no substitution of O2- and OH- in clay layers?

No substitution

Do the ...hedra ever vary?

No, never

Can the centers of tetrahedra and octahedra vary?

Yes, lots depending on who is around

What is isomorphic substitution?

The shapes (tetrahedra and octahedra) stay the same while the cations change.

In isomorphic substitution, what are subject to negotiation and are substitutable?

Cations

In 2:1 layers of minerals, what are commonly substituted for the cations that should have been in the hedron?

Slightly less positive cations

Ex) Mg2+ instead of Fe3+

Cation in center of hedron are replaced with a cation of what size in relation to the original cation?

A similar size cation

What does it mean when a sheet gets a negative permanent charge?

A cation with less (+) charge substitutes for one with more.

Ex) Mg2+ replacing Al3+

What does it mean when a sheet gets a positive permanent charge?

A cation with more (+) charge substitutes for one with less.

Ex) Al3+ replacing Fe2+

Which is more common in soils, negative permanent charge or positive permanent charge? Why?

Negative permanent charge

Because most positively charged ions like Si wash out of soil over time.

Is muscovite mica a primary mineral?

Yes

What happens to mica during 2:1 assembly?

It becomes net negative

Because every 4th Si4+ is replaced by an Al3+, making the layer more net negative

What ion are mica minerals formed with?

K+ ions

Why are mica satisfied by K+ ions?

Mica have a negative permanent charge that the K+ satisfy

Unlike expanding clays, what is the glue between mica layers?

dry K+

In primary chlorites, tetrahedral sheets replace what with what?

Si4+ is replaced by an Al3+

What satisfies the (-) charge of a chlorite sheet?

A whole (+) charged trioctahedral sheet

What balances out the (-) charges due to isomorphic substitution in chlorites and serves as the glue?

An independent trioctahedral sheet (no shared O) with built in (+) charges due to isomorphic substitution of Al3+ instead of Mg2+

Primary minerals with 2:1 layers. (mica and chlorites) have many or few isomorphic errors in their layers?

Many

What do isomorphic errors mean for layers?

More negative spots

Can nutrient cations dock on negative spots on 2:1 layers? Why?

No

Because the glue is too tight between layers so the cations can't see the negative spots

Which colloid has the tightest glue? Why?

Chlorite and Illite (fine grain micas)

Because balancing of (-) charge

Which 2 colloids are expanding?

Smectite (max. swelling) and Vermiculite (some swelling)

Which colloid has maximum swelling?

Smectite

Which 2 colloids are nonexpanding?

Illite and Chlorite (both min. swelling)

What is the glue of smectite?

water molecules and random cations

What is the glue of vermiculite?

water molecules, Mg2+, and other ions

What is the glue of illite?

K+ ions

What is the glue of chlorite?

hydroxide sheet

What happens as young clays (illites and chlorites) age?

Edges fray (weathering) and the glue becomes exposed to the soil solution

Ex) in illite, new cations can replace former K+ glue

What is mica?

Weathered illite

Which colloids have dry glue?

illite and chlorite

What do dry glues do that other glues don't?

They keep the 2:1 layers so close together that water molecules can't squeeze in, except near frayed edges

What happens as weathering progresses?

Edges become more frayed and water can enter deeper and deeper into the interlayer region

What happens when only a few "spot welds" of the original dry glue remain?

A clay like vermiculite is formed that can shrink and swell a bit

What can shrink/swell clays do?

Hold water and other nutrients

What happens when all the dry glue is gone?

Smectite is formed. It shrinks and swells a ton when wetted.

Is smectite good or bad for construction?

bad

Can shrink/swell clays hold K strongly?

No

Can shrink/swell clays hold anything very strongly?

No

Since shrink/swell clays can't hold anything very strongly, what happens to the interlayer?

Water and other cations will rush in to fill charge, making it less permanent

What is the second process that begins after some of the dry, fixed K+ glue got weathered out of the mica's interlayers?

Repair of isomorphic substitution errors in the tetrahedral sheets

What happens to places in the tetrahedral sheet with trapped negative charges over the centuries?

These places will dissolve and leave divots in the sheet.

How do divots in the tetrahedral sheets get repaired?

Ions enter the interlayer via the water and bring patching material (like silicate anions such as H3SiO4-) that fill the divots

Isomorphic substitution error repairs are only relevant for which minerals?

Those with tetrahedral isomorphic substitution

This explains the increasing (+) charge that comes from going from muscovite (primary mineral mica) to beidellite (old smectite clay)

Are errors in the octahedral layer easier or harder to repair than those in the tetrahedral sheets? Why?

Harder

Because they are sandwiched inside the tetrahedral sheets

How are more weathered minerals affected ?

More water and organic matter can get in the mineral layers, thus increasing their shrink/swell potential.

What happens to the mineral and its charge as the amount of Al ion goes down and Si goes up in a tetrahedra?

Muscovite (primary mica mineral mica) turns to Beidellite and the charge becomes less negative

What happens to errors in the tetrahedral sheets as primary mica mineral (muscovite) weathers into clay?

Errors in the sheets get repaired

What happens to the charge per unit formula as errors in the tetrahedral sheets get repaired?

It gets reduced

What is Kaolinite's glue?

Hydrogen bonds

What is Kaolinite good for? Why?

ceramics, construction, and cultivation

Because it is not too heavy or sticky & when wet is good for planting

What is illite's glue?

K+

What is illite's shrink/swell tendency because of it's K glue?

Minimal shrink swell tendency

Okay to build on because of this.

What is vermiculite's glue?

Some K, mostly cations

What is vermiculite good for?

Okay but not great for construction and cultivation, but holds lots of nutrients.

Why is vermiculite good at holding onto water and nutrients?

Water and nutrients rush into the interlayers to balance the charge of the interlayers

What is smectite's glue?

Cations

What is smectite bad for?

Construction, pottery, and cultivation

What is smectite good for?

Plugging holes

Ex) fill in a well

Why is smectite bad for construction?

The bonds between layers are so loosely held that lots of water comes in and whatever cations can bind will bind. This means they will shrink and swell a ton which is bad for construction.

Do basic solutions have a high or low pH?

High

What does a high pH mean in terms of anions in a solution?

Lots of hydroxyl anions (OH-) in solution

What does basic OH- do to protons (H+) from clay octahedra?

They pluck them from the clay octahedra.

When basic OH- pluck H+ from clay octahedra, what happens to the charge on the mineral?

A negative charge gets left on the O in the mineral.

OH- of soil solution wants what?

H+ protons

When protons (H+) are plucked off the octahedra, what happens to the O2? What does this mean for surrounding cations?

It becomes negative.

Surrounding (+) charge cations can hold onto the octahedra, which plants like

Is H+ attracted or repelled form O2?

Attracted

Under acidic conditions, what charge does O2 have? Why?

Positive charge

Because extra H+ are present and attracted to the O2

Do lots of minerals have positive or negative variable charge due to acidic soil?

positive variable charge

Are there few or many H+ in an acidic solution? Is the pH high or low?

Many

Low

In acidic conditions (many H+) what happens to the H+?

H+ hop onto octahedral OH, making water

When H+ hop onto octahedral, what charge is left on the mineral?

Positive (+) charge

Why do soil minerals hold on to positive cations?

Because of internal charge (-)

What can Al hydroxy cations do to clay minerals?

Satisfy the negative charge

What is the charge of aluminum complex? (just like a proton)

+1

What can a OH- do to the aluminum hydroxy ion?

Can pluck it off, leaving behind a free (-) charge on the mineral surface

What does Al do to a spot that nutrients could bind to under acidic pHs? What does this mean for plants?

Blocks the spot so nutrients can't bind

Bad for plants

What does Al do to soil? What does this mean for the acidity of the soil?

Removes an OH-

Acidifies the solution