mineral structures

colloid

a homogenous mixture consisting of ultramicroscopic particles of one substance dispersed through a second substance

particles dont settle, and cannot be separated out

Ex OM in clay or silt/sand

minerals

unconsolidated rock, crushed

have different hardiness, rate on scale 1-10

weather at different rates

rock types

igneous, metamorphic, sedimentary (Alta)

different types have different minerals within, these have different elements and therefore impart different properties to soil

sedimentary rock

mostly found in AB, high base cations

calcareous soil = high base saturation

weathering

primary minerals into secondary minerals

can be physical, chemical or biological

physical weathering

disintegration, freeze/thaw cycles

chemical weathering

decomposition, molecular changes

water is universal solvent - can dissolve certain structures

biological weathering

decomposition mediated by organisms

enzymes and organic acids

primary minerals

sand and silt

other ex: quartz, mica, biotite, feldspar, albite

secondary minerals

clay

via weathering of primary minerals

quartz

primary

SiO2, silicate framework (of all soil)

predominately sands

very hard

Feldspar

Na+, K+, Ca2+, Mg2+ - base cations

bonded to silicate framework

decreasing hardiness

Micas

no silicate framework

least hardy

Moscorite (white), Biotite (black)

sandy soils

high in quartz

coarse texture

fine soils

high in micas

clay terminology

soil separate, particle size <2 micrometers, textural class, secondary mineral, component of colloidal fraction with OM

soil colloids

particles less than 1-2 micrometers, huge SA compared to weight, electronegative surface charge (dominant), micelles absorb thousands of cations within water - attracted to surface, CEC, ionic double layer

phyllosilicates dominant in AB

Cation exchange capacity (CEC)

occurs when ions break away into soil solution and are replaced by other ions

ionic double layer

negatively charged micelle surrounded by swarm of cations (each one enclosed in h2o)

amorphous clays

non crystalline silicate clays - allophane and imogolite are present in volcanic soils

fe and al oxides in colloids

Fe and Al atoms connected to oxygen atoms and hydroxyl (OH) groups, may be either amorphous or organized in crystalline sheets

mostly present in more weathered soils (dominant in BC or QC)

OM in colloids

key driver of soil function high

high function = health

silicon tetrahedron

building block of silicate clay mineral

4 faces, central cation is Si4+

Si will replace Al 3+ and result in -1 net charge

aluminium octahedron

building block of silicate clay mineral

8 faces, central cation Al 3+

Mg 2+ will replace Al 3+ w -1 net charge

2:1 clay

two tetrahedron sheets, with an octahedron sheet in the middle

1:1 clay

one tetrahedral sheet and one octahedral sheet

element substitution in silicate clays

replacement of central cation during weathering

Si 4+, Al 3+, Mg 2+ as central cations (all similar sizes)

Si replaced as central cation, leads to differences in surface charge

isomorphic substitution

replacement of central cations of similar size but different charge (valence)

Al replaces Si, Mg replaces Al

leads to CEC, buffering capacity, fertility or nutrient availability

not pH dependent, permanent charge - more it happens the more charge occurs