Ch. 2- Weathering, Erosion, and minerology Flashcards
Weathering
The destructive process(es) by which rocks/minerals break down/dissolve on earth’s surface
Erosion
the process(es) whereby rocks/minerals are broken down/dissolved and simultaneously transported by natural forces.
Mechanical Weathering
the process of rocks breaking down by physical means without changing their chemical composition
Types of Mechanical Weathering
- unloading & exfoliation
- freezing and thawing
- growth of crystals
- thermal expansion and contraction
- root wedging
- burrowing animals
Unloading and Exfoliation
Allows rock to expand vertically as opposed to horizontally, as pressure is not removed from all sides (Just the top!);
Forms tiny joints /fractures parallel to surface, creates planes of weakness that peel away from the rest of the rock
Freezing and Thawing
Expansion & Contraction- Water seeps into cracks/fractures that were formed, where it will freeze and unthaw, forcing cracks open like a splint
Growth of Crystals
Occurs from sea spray hitting a rock, causing salt crystals to grow in the cracks
Thermal Expansion and Contraction
rocks expanding when heated and contracting when cooled– most prominent in desert environments
Wetting and Drying
If minerals can absorb water, they will expand and cause pressure on the rock– similarly, if rock dries out, the minerals will contract
Root wedging
Water seeping deeper into rock and splitting the rock, causing the root of a plant to follow the water.
Burrowing Animals
animals burrowing their way into solid rock for nutritional/habitat purposes
ex. mollusk drilling their ways into solid rock for homing; some tusked mammals get some of their nutrients from drilling into rock as well.
Chemical Weathering:
a process that breaks down rocks and minerals through chemical reactions
When is chemical weathering the most efficient?
If the surface of a rock is already sufficiently weathered.
Grain sizes:
- > 2mm: boulders, gravel, pebbles
- 1/16-2mm: sand
- 1/256-1/512mm: silt
- <1/512mm: clay
What is a special property that clay and silt exhibit?
electrostatic cohesion
Types of Chemical Weathering (Reactions)
- Spheroidal Weathering
- Redox reactions
- Hydrolysis Reactions
- Carbonation reactions
- Hydration Reactions
- Ion-Exchange Reactions
- Chelation
Redox Reactions
involving the gain or loss of electrons from atoms
Hydrolysis Reactions
Breakdown of minerals by adding water (H+)
Hydration Reactions
Reactions of minerals with water, adding it but not necessarily breaking bonds
Carbonation reactions
the reaction of minerals with dissolved CO2 in water
Chelation
Reaction between a metal ion and a complexing agent
What is the first biological agent to find a weathered rock?
Lichen
Complexing agents (in/decrease) the activity of the ion and (in/decrease) the stability of the solution.
decrease; increase
Ion-Exchange reactions
generally involving the substitution of loosely bonded ions absorbed onto mineral surfaces
Factors affecting electron mobility (4)
- Ionic Radius
- Ionic Charge
- pH
- Eh (oxidation potential)
Differential weathering:
materials that are more susceptible to weathering in materials that are less-so
What are the most common minerals on Earth?
silicate minerals
Silicate Minerals compose what parts of the earth?
Oceanic crust and mantle
Clay minerals are hydrated silicates of __, __, and __, and are arranged in sheets of ___ tetrahedra and ___ octahedra
Al; Fe; Mg; Si; Al;
In clay minerology, a rectangle represents…
Aluminum
In clay minerology, a rhombohedron represents…
Silica
____ or ____ can join 2:1 structures together, forming 2:1:1 structures:
water or potassium
Common clay sized minerals and their weathering sequence:
- Sulfates, Chlorides
- Carbonates, Phosphates
- Silicates
- 2ndary Clays
- Oxides
Sulfates/Chlorides
-Gypsum
-Halite
Carbonates, Phosphates
- Calcite
- Dolomite
- Aragonite
- Apatite…
Silicates
Bowens reaction series (OPAB, Feld, Musc, Quartz)
Secondary Clays
-Vermiculite
-Montmorillonite
-Kaolinite
Oxides
Think: what mineral is most commonly present in red/oxidized rocks?
- Gibbsite (Al Oxides)
- Hematite (Fe Oxides)
- Zircon (Ti oxides)
Factors affecting weathering
- Parent material (mineral stability, permeability, joins/fractures)
- Climate
- Vegetation
- Topography
- Time
