- eventually breaks down rx to form sediments in rivers, beach sand, and soil.
- 2 types: Mechanical and chemical

Mechanical Weathering:

- breaks rocks by physical forces into smaller and smaller pieces, each retaining the characteristics of the original piece.

Frost Wedging: Alternate freeze and thawing.

- water expands 9% when it freezes.

- creates and outward force.
- in nature, water gets down into cracks and fissures in rx, expands, and enlarges the openings. Cycles over and over again the rx finally break into smaller fragments.
- in mountainous regions, this ends up producing a talus slope which forms at the base of steep outcrops.

Unloading:

- when large masses of igneous rx are exposed (like Table Rock, SC), it tends to exfoliate like an onion - skin by skin. This is termed sheeting.

- thought to occur because of the reduction of overlying pressure as the outer layers of rx are stripped away.
- fractures develop parallel to the surface topography, giving the outcrop a domed look. Domes are termed exfoliation domes.

Thermal Expansion:

- Heating and cooling of rx in very hot desert regions cause stress on the outer surface of rx. Eventually, the outer shell will crack and fall off.

Organic Activity:

- Plant roots grow into rx fractures in search of water and mineral nutrients. As roots grow, fractures widen.
- Burrowing animals move fresh material to the surface, allowing it to weather quicker than it would undergound.
- Decaying organisms produce acids, which contribute to chemical weathering.

Chemical Weathering:

- alters internal structure of mins by removing/adding elements.

- can oxidize (like rust on a fender) and make a material weak & friable.
- combines w/CO2 to form carbonic acid: H2CO3
- orthoclase weathers into clay & silica when reacts w/H2CO3.

- Quartz is very resistant, doesn't weather easily.

quartz --> quartz
feldspars --> soft clay minerals
amphibole --> clay, hematite
olivine --> hematite

- resistance to weathering is just the opposite of Bowen's Reaction Series.

- olivine is least resistant, while quartz is most resistant.
- termed differential weathering (+ avaiability of joints, climate, mins, etc.)
- causes spectacular formations in some places.

- climatic factors (temp, avail of water, altitude, etc. affect the rate of weathering.

- chemical weathering can cause angular fragments in a rock mass to become rounded and take on a spherical shape.

- attacks the corners & edges first (greater surface area available) - called spheroidal weathering.