Title: Mineral Weathering and Secondary Mineral Formation weathering: chemical alteration of minerals in so
1 Mineral Weathering and Secondary Mineral Formationweathering chemical alteration of minerals (in soils involves water gases acids etc).
Parent material soil
Desilication via weathering
Parent Materialprimary silicates formed from igneous/metamorphic processes
Soil secondary silicates oxides carbonates etc.formed from weathering processes
2 Behavior of Elements During Chemical Weathering
Soils are depleted in elements relative to parent material
Element loss/depletion is determined by elements position on periodic table (which column or group of columns) AND the elements ionic potential
Z/R ionic potential zcharge rradius
Z/R 0-3 ion surrounded by H2O shell soluble in H2O (Na Ca etc)
Z/R3-9.5 ion so strongly attracts H2O that insoluble oxides/hydroxides form (Al Fe)
Z/Rgt9.5 soluble oxyanions form (S C etc.)
3 (No Transcript) 4 Ionic potential of important elements
Red arrow indicates decreasing attaction to H2O within a group of elements
Decreasing attraction is reflected in weathering losses..
5 Element loss varies with ionic potential Ti group Alkali metals and alkaline earths 6 Mineral Particle Size and Mineralogy
Gravel gt 2mm (primary)
Sand gt 0.05 to 2.0 (primary)
Silt lt0.05 to 0.002 (primary secondary)
Clay lt 0.002 (secondary)
Most secondary mineral are silicates and most secondary silicates are phyllosilicates.
7 (No Transcript) 8 (No Transcript) 9 11 phyllosilicates kaolinite
One layer of Si tetrahedra
One layer of Al octahedra
Individual minerals are held to another via H bonds
10 21 Phyllosilicates di and trioctahedral
Substitution of 2 for 3 in octahedral layer (called isomorphous substitution)
Creates a net negative charge (and property of cation exchange capacity)
Results in expandable layers
Substitution of 3 for 4 in tetrahedral layer
Also has CEC but little or no expansion
11 Other secondary mineral groups oxides
Al oxides (gibbsite)
Results of vigorous chemical weathering (desilication)
12 Non-silicate secondary minerals oxides
Acidic OM-rich envir.
Warm dry environments
13 Non-silicate secondary minerals carbonates
Ca is released from some weathering source
Forms in arid to semi-arid environments when soil solution becomes saturated
Presence in upper 1m related to MAP
Depth of carbonate layer related to MAP
14 Geographical distribution related to climate
Greater than 100cm/yr removes carbonate
Below 100cm depthMAP
15 Non-silicates sulfates (gypsum)
Presence of sulfates in soils usually occurs in hyperarid climates (or sites with high water table and evaporative enrichment of salts)
16 Secondary Minerals in California Soils Sierra Nevada 17 Soil Mineralogy vs. Elevation
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