Aim: What factors cause chemical weathering?

Describe what you see and hypothesize how it got this way…

A. Chemical weathering 1. Rock is broken down by chemical changes 2. Rock is changed to different minerals and becomes weaker. Gravestone made of limestone has been weakened by carbonic acid and weathered away. Granite withstands the effects of chemical weathering better.

B. Causes of chemical weathering:

1. Water ***most important factor for chemical weathering*** a. Water dissolves minerals OR b. Water changes the material into a different mineral (hydrolysis) AND c. Water speeds up chemical reactions

Chemical weathering on feldspar http://www.classzone.com/books/earth_science/terc/content/visualizations/es1202/es1202page01.cfm?chapter_no=visualization

2. Carbonation Carbon dioxide from air dissolves in water to make carbonic acid. Carbonic acid reacts with minerals in rocks, like calcite in limestone, which produces weaker materials that dissolve away in water.

Ex. - Caves Limestone (organic, sedimentary) is dissolved by water seeping from above. The limestone has been weakened by carbonic acid. Caves, stalactites and stalagmites can form.

Ex. - Sink Holes Surface water seeps down and dissolves away the rock.

Ex. - Karst Topography http://www.classzone.com/books/earth_science/terc/content/visualizations/es1405/es1405page01.cfm?chapter_no=visualization A complex area of underground caves and sinkholes, formed by the continued weathering of limestone, dolomite or marble (rocks made of calcite).

3. Oxidation Oxygen causes oxidation of metals: rusting Oxygen and iron react to make iron oxide (rust) Rocks appear red from oxidation

Why is the statue of liberty green? Oxidation of copper makes cupric oxide… a green color.

Water speeds up oxidation But Oxygen is the key ingredient…

4. Living Organisms Lichens are an organism that will grow on rocks and release an acid that breaks down the rock.

5. Pollution a. Acid rain is created by water reacting with products of the burning fossil fuels and by some natural events like volcanic eruptions. b. Acid rain dissolves minerals of rocks like limestone and marble.

Acid rain

The areas of greatest acidity (lowest pH values) are located in the Northeastern United States. This pattern of high acidity is caused by the large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain.                                

Devil’s Marbles Huge slabs of granite chemically weathered by water in the cracks gives them this rounded appearance.

More Devil’s Marbles

Which chemical weathering agents might have changed Cleopatra’s needle?

Summary: What climate factors will affect chemical weathering? In other words, what speeds up chemical weathering? Which type of chemical weathering can also be considered organic or biological?