Title: Mineral Weathering and Secondary Mineral Formation weathering: chemical alteration of minerals (in soils, involves water, gases, acids, etc).
1Mineral 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
2Behavior 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
- Classes
- 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)
4Ionic potential of important elements
- Red arrow indicates decreasing attaction to H2O
within a group of elements - Decreasing attraction is reflected in weathering
losses..
5Element loss varies with ionic potential
Ti group
Alkali metals and alkaline earths
6Mineral 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)
911 phyllosilicates kaolinite
- One layer of Si tetrahedra
- One layer of Al octahedra
- Individual minerals are held to another via H
bonds
1021 Phyllosilicates di and trioctahedral
- Dioctahedral (smectites)
- 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
- Trioctahedral (vermiculite)
- Substitution of 3 for 4 in tetrahedral layer
- Also has CEC, but little or no expansion
11Other secondary mineral groups oxides
- Al oxides (gibbsite)
- Results of vigorous chemical weathering
(desilication)
12Non-silicate secondary minerals oxides
- Fe oxides
- Geothite
- Yellowish brown
- Acidic, OM-rich envir.
- 2. Hematite
- Bright red
- Warm, dry environments
13Non-silicate secondary minerals carbonates
- Calcite
- 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
14Geographical distribution related to climate
- Greater than 100cm/yr removes carbonate
- Below 100cm, depthMAP
15Non-silicates sulfates (gypsum)
- Presence of sulfates in soils usually occurs in
hyperarid climates (or sites with high water
table and evaporative enrichment of salts)
16Secondary Minerals in California Soils Sierra
Nevada
17Soil Mineralogy vs. Elevation