W2 Phyllosilicate clay minerals

sand and silt particles consist of largely…

primary minerals

Clay particles consist mainly of,,,

secondary minerals

secondary minerals result from…

weathering of primary minerals either by alteration in the structure or from re-precipitation of the products of weathering (dissolution) of primary minerals

common secondary minerals in soils are

• silicate clay minerals, including group of phyllosilicates

• soluble minerals, including the group carbonates and the group sulfates

• various oxides and hydrous oxides of Al, Fe, Mn or sesquioxides

• amorphous (non-crystalline) aluminosilicates 

phyllosislicate clay minerals

sub-group of silicates (an extensive group of minerals which are derived from silica SiO₂).

• with building blocks of tetrahedrons ( si surrounded by 4 oxygen)

• and octahedron - Al is surrounded by 6 oxygen

isomorphic subsitution

ion fills a position previously filled by another ion of a similar size and valence wihtin the crystaline structure = permenat charge on clay minerals

ideal vs not so ideal 2(Tetra):1 (octa) phyllosilicate

• ideal = no net charge

• not so ideal = permenat charge on clay mineral due to isomorphic susbsitution

Common types of 2:1 phyllosilicate minerals belong to the following groups:

• smectite group- mineral montmorillonite as most common mineral in this group

• illite or fine-grained mica group

montmorllite

2:1 phyllosislciate clay minineral

• 2 si-tetrahedral sheets with 1 al-octahedral sheet btwn them

• involves isomorphic substitution of Mg for some Al in the octahedral sheet.

• = permeneative negative charge

are layers within montmorlite weak or strong

weak

• loosely held together by very weak cation-to-oxygen bonds

• between layers, negative oxygens face eacother = repulsion

charcertstcs of montmorlite clay

• high SSA to attract ions

  • external and internal surface

• sticky

• reactive

• shrink swell clay

chemical characterstics of kalonite

• least reactive/most stable

• least negative chares

soil colloids

Particles that have both charged surfaces and large specific surface area are very reactive (or chemically active)

types of soil colloids

• phyllosilicate clay minerals

• oxides and hydrous oxydes of Fe and Al

• amorphous minerals

• organic colloids.

what is an outcome of soil mineal and organic particles being charged

their interaction and arrangement leads to formation of distinct structural units called peds or aggregates

common types of soil colloids include

• phyllosilicate clay minerals

• oxides and hydrous oxydes of Fe and Al

• amorphous minerals such as allophane and imogolite, and

• organic colloids.

characterstics of kalonite

• low SSA - only external surfaces

• very little or no isomorphic substitution, resulting in no permanent charges.

  • least - charge = stable

• less plasicilty

• less sticky

• holds less water

why is kaolinte non expanding mineral

layers tightly bound by H-bonding = only external surface exposed for reactions with other ions

mont vs kalonite : layer strength

• mont = weak

  • layers bound by weak cation to oxygen bonds

• kal = strong

  • layers bound by H-bonding

mont vs kalonite : water content, interlayer spacing and SSA

• mont = affected

  • interlayer spacing chanes with water

  • expanded state = higher SSA to attract ions

• Kalonite = not affected

  • interlayer spaces doesnt change

  • only external surface area = lower SSA

mont vs kalonite reactivty and stickiness

• mont = sticky and reactive

• kal = not sticky and stable

mont vs kalonite : charge/.isomorphic sub

• mont = more isomorphic sub = more neg. charges

• kal= little to no isomorphic sub= low # of neg charges