Chemical + Biological Weathering Flashcards
Oxidation
Some minerals in rocks react with oxygen, either in the air or in water. Iron is especially susceptible to this process. It becomes soluble under extremely acidic conditions and the original structure is destroyed. It often attacks the iron-rich cements that bind sand grains together in sandstone.
Carbonation
Rainwater combines with dissolved carbon dioxide from the atmosphere to produce a weak carbonic acid. This reacts with calcium carbonate in rocks such as limestone to produce calcium bicarbonate, which is soluble. This process is reversible and precipitation of calcite happens during evaporation of calcium-rich water in caves to form stalactites and stalagmites.
Solution
Some salts are soluble in water. Other minerals, such as iron, are only soluble in very acidic water, with a pH of about 3. Any process by which a mineral dissolves in water is known as solution, although mineral-specific processes, such as carbonation, can be identified.
Hydrolysis
This is a chemical reaction between rock minerals and water. Silicates combine with water producing secondary minerals such as clays. Feldspar in granite reacts with hydrogen in water to produce kaolin (china clay).
Hydration
Water molecules added to rock minerals create new minerals of a larger volume. This happens to anhydrite forming gypsum. Hydration causes surface flaking in many rocks, partly because some minerals also expand by about 0.5 percent during the chemical change as well because they absorb water.
What is chemical weathering?
Chemical weathering is the result of chemical reactions between the elements of the weather and some minerals within the rock. It may reduce the rock to its chemical constituents or alter the chemical and mineral composition of the rock.
What do chemical weathering processes produce?
Chemical weathering processes produce weak residues of different material that may then be easily removed by erosion or transportation processes.
What is Van’t-Hoff’s Law?
Van’t-Hoff’s Law states that a 10°C increase in temperature leads to a 2.5 times increase in the rate of chemical reaction (up to 600°C), so most chemical weathering processes are most effective in warm or hot climatic regions.
In what type of climate are chemical weathering processes most effective?
Chemical weathering processes are most effective in warm or hot climatic regions. This is why warm, moist tropical environments experience the fastest rates of chemical weathering and cold, dry locations the slowest.
What is the importance of weakly acidic water in chemical weathering?
Some weathering processes are especially important when rocks are in contact with weakly acidic water.
What issue is associated with climate change and increasing levels of atmospheric CO2?
One issue associated with climate change and increasing levels of atmospheric CO2 is that rain, and therefore ice, is becoming more acidic. This can lead to increased rates of chemical weathering in affected areas.
What is the role of plants in glacial environments?
In glacial environments, plants are usually not present due to the harsh conditions, so biological weathering is not as significant as other types of weathering.
What is chelation in biological weathering?
Chelation is a chemical process in which organic acids produced by organisms (e.g. lichens and fungi) react with metal ions in rock minerals, removing them from the mineral structure and breaking down the rock.
What organisms are involved in chelation?
Organic acids produced by organisms such as lichens and fungi are involved in chelation.
