Weathering

What is created during the oxidation of minerals?

Hematite and limonite

Does chemical weathering slow down or speed up mechanical weathering? Why/how?

Chemical weathering contributes to mechanical weathering by weakening the outer portions of some rocks, which in turn, makes them more susceptible to being broken by mechanical weathering processes.

Explain how each of the following can speed up/ slow down the weathering rate: wet climate:

Climates where there is abundant moisture with warm temperatures. chemical weathering is sped up.

Explain how each of the following can speed up/ slow down the weathering rate: permeability:

If is water is able to pass through the rock easier then the rock will likely weather faster.

What causes acid mine drainage?

In a moist environment, chemical weathering of pyrite yields sulfuric acid and iron oxide. In many mining locales this weathering process creates this serious environmental hazard, particularly in humid areas where abundant rainfall infiltrates spoil banks.

Which important minerals are produced (along with dissolved ions)?

Quartz grains, clay minerals, hematite, limonite. Silica, K, Na, Ca, Mg

Which common minerals are weathered?

Quartz, Feldspars, Amphibole, and Olvine

What is rusting?

Rusting is essentially a process of oxidation in which iron combines with water and oxygen to form rust, the reddish-brown crust that forms on the surface of the iron.

Define erosion (and its end product):

The removal and transport of rock particles at the Earth's Surface.

Describe oxidation of minerals:

The removal of one or more electrons from an atom or ion. So named because elements commonly combine with oxygen.

How do salts, carbonates, sulphates, phosphates weather?

They are water soluble and they are dissolved

Explain how each of the following can speed up or slow down the weathering rate: rock strength:

Weaker rocks are more likely to weather faster than stronger rocks.

Does mechanical weathering slow down or speed up chemical weathering? Why/how?

When a rock is mechanically weathered and broken into smaller pieces, the amount of surface area is increased that is available for chemical weathering to occur.

Explain 4 ways that rocks can be mechanically weathered:

1. Create new fractures, expand existing fractures 2. Freeze-thaw cycles, makes potholes 3. Plant roots force fractures open 4. Sandblasting by wind or water

Describe hydrolysis:

A chemical weathering process in which minerals are altered by chemically reacting with water and acids.

What is dissolution?

A common form of chemical weathering it is the process of dissolving into a homogeneous solution.

What is the nasty end-product of the oxidation of minerals?

Acid mine drainage

Explain how each of the following can speed up/ slow down the weathering rate: presence of soil:

Adds acid to water protect from frost absorption

What mineral resources are produced by weathering?

All aluminum ore and some iron ore.

Why is the next lecture (soils) dependent on this one?

All soils are created by weathering.

Explain how each of the following can speed up or slow down the weathering rate: minerals present:

An example of this a headstone of granite which is composed of silicate minerals are relatively resistant to chemical weathering. In contrast, marble headstones show signs of extensive chemical alteration over a relatively short period. Silicates, the most abundant mineral group, chemically weather in essentially the same order in which they crystallize.

Explain how each of the following can speed up/ slow down the weathering rate: planes of weakness:

An example of this are joints

Define spheroidal weathering:

Any weathering process that tends to produce a spherical shape from an initially block shape

Explain how each of the following can speed up/ slow down the weathering rate: hot climate:

Arid regions where there is insufficient moisture to promote rapid chemical weathering, but if it is warm and wet there is a more optimal chance for weathering.

Why is groundwater in/below soil even more acidic?

As acidic rainwater sinks into the ground, carbon dioxide in the soil may increase the acidity of the solution. Various organic acids are also released into the soil as organisms decay, and the presence of sulfuric acid.

List ways that humans can increase the rate at which a rock weathers:

- Exposure of rocks by excavation - Acid rain - Acid groundwater contamination - Changes in groundwater percolation

How can weathering damage built structures

- It can weaken the foundation support - Weaken the slope stability - Weathering of building materials stone, cement, gravel

Why are halite (rock salt) and calcite/limestone very easily chemically weathered and eroded?

Halite readily dissolves in water because, although this compound maintains overall electrical neutrality, the individual ions retain their respective charges. Calcite dissolves in water containing carbon dioxide

Why does weathering correlating with Bowen's Reaction Series make sense?

In general, minerals are most stable at the temperature and pressure at which they form. In the case of the igneous rock minerals described in Bowen's Reaction Series, the higher temperature minerals (such as olivine, pyroxene, etc.), when exposed at the surface, will be farthest from their comfort zone, and will therefore chemically weather at a faster rate. Quartz, at the other end of Bowen's, is closer to its preferred temperature and should therefore be more stable (and it is)

What is the role of acid in hydrolysis?

In nature water usually contains other substances like acid that contribute additional hydrogen ions, thereby greatly accelerating hydrolysis.

Explain how each of the following can speed up/ slow down the weathering rate: cold climate:

In polar regions, chemical weathering is ineffective because frigid temperatures keep available moisture locked up in ice.

Define chemical weathering

Involves a chemical transformation of rock into on or more new compounds.

What is natural carbonic acid?

It is created when carbon dioxide in the atmosphere dissolves in raindrops.

Are mafic minerals easier or harder to weather than felsic minerals?

Mafic minerals are the easiest minerals to be chemically weathered and felsic are the hardest

Why is rain acidic?

Normal" rainfall is slightly acidic because of the presence of dissolved carbonic acid. Acid rain can also be caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

Which important minerals are weathered during the oxidation of minerals?

Olivine, pyroxene, hornblende, and biotite

What two chemicals make up ~99% of Earth's atmosphere? Which are chemically reactive?

Oxygen and Nitrogen

What two chemicals at Earth's surface are most important in chemical weathering?

Oxygen and Water

What are the most common soil and sedimentary minerals?

Silicates, clay minerals

What is human- caused acid rain?

Sulfides and nitride emissions creates acid rain.

Why is hydrolysis the most important weathering process?

The most common mineral group, the silicates, is decomposed primarily by the process of hydrolysis.

Define weathering (and its end products):

The physical breakdown and chemical alteration (decomposition) of rock exposed to Earth's surface into minerals or smaller chunks.

Define mechanical weathering

The physical forces that break down rock into smaller pieces without changing the rock's original composition.