Pyrite reacts with water and oxygen to form sulphuric acid, as follows:. Some of the worst examples of ARD are at metal mine sites, especially where pyrite-bearing rock and waste material have been mined from deep underground and then piled up and left exposed to water and oxygen. One example of that is the Mt. At many ARD sites, the pH of the runoff water is less than 4 very acidic. Under these conditions, metals such as copper, zinc, and lead are quite soluble, which can lead to toxicity for aquatic and other organisms.
For many years, the river downstream from the Mt. Washington Mine had so much dissolved copper in it that it was toxic to salmon. Remediation work has since been carried out at the mine and the situation has improved. The hydrolysis of feldspar and other silicate minerals and the oxidation of iron in ferromagnesian silicates all serve to create rocks that are softer and weaker than they were to begin with, and thus more susceptible to mechanical weathering.
Some weathering processes involve the complete dissolution of a mineral. Calcite, for example, will dissolve in weak acid, to produce calcium and bicarbonate ions. The equation is as follows:. Jeannie Evers, Emdash Editing. Caryl-Sue, National Geographic Society. For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher.
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The rock cycle is a web of processes that outlines how each of the three major rock types—igneous, metamorphic, and sedimentary—form and break down based on the different applications of heat and pressure over time. For example, sedimentary rock shale becomes slate when heat and pressure are added. The more heat and pressure you add, the further the rock metamorphoses until it becomes gneiss.
If it is heated further, the rock will melt completely and reform as an igneous rock. Empower your students to learn about the rock cycle with this collection of resources. An element is a substance that cannot be broken down into a simpler format. They are distinguished by a unique atomic number.
The elements are organized by their atomic number in the periodic table, which highlights elements with similar properties. Water is an example of a compound, a mixture of two or more elements, and is created when two hydrogen atoms bond to an oxygen atom. Use these resources to examine the properties and uses of elements and compounds.
Weathering is the process of the weakening and breakdown of rocks, metals, and manmade objects. There are two main types of weathering: chemical and physical. An example of chemical weathering is acid rain. Caused mostly by the burning of fossil fuels, acid rain is a form of precipitation with high levels of sulfuric acid, which can cause erosion in the materials in which it comes in contact.
An example of physical weathering is wind blowing across the desert playas. This process causes rocks to form a specific pyramid-like shape and they are called ventifacts. Select from these resources to teach about the process of weathering in your classroom.
Sedimentary rocks are one of three main types of rocks, along with igneous and metamorphic. Metamorphic rocks start as one type of rock and—with pressure, heat, and time—gradually change into a new type of rock. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Weathering describes the breaking down or dissolving of rock s and mineral s on the surface of the Earth.
Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. Once a rock has been broken down, a process called erosion transports the bits of rock and mineral away. No rock on Earth is hard enough to resist the forces of weathering and erosion. Together, these processes carved landmark s such as the Grand Canyon, in the U.
This massive canyon is kilometers miles long, as much as 29 kilometers 18 miles wide, and 1, meters 1 mile deep. Weathering and erosion constantly change the rocky landscape of Earth. Cations are positively charged ions; ions are charged atoms with too many or too few electrons.
The cations include the iron, magnesium, aluminum, sodium, potassium, and calcium ions that form the common silicate minerals along with silicon and oxygen. Soluble silica H 4 SiO 4 and metal cations e. Clay minerals are very small sub-microscopic solid particles. They are sheet silicate minerals like micas. Quartz chemically weathers only very, very slowly because of its high stability.
Authors Authors and affiliations Isabel M. Duarte Celso S. Reference work entry First Online: 01 August How to cite. Synonyms Chemical action; Chemical alteration; Chemical decomposition; Chemical process; Chemical reactions. This is a preview of subscription content, log in to check access. In: Weathering: its products and deposits, vol vol II. Aleva GJJ Laterites: concepts, geology, morphology and chemistry.
Anon The description and classification of weathered rocks for engineering purposes Geological Society Engineering Group working party report. Elsevier, Amsterdam, p Google Scholar. Chorley RJ The role of water in rock disintegration.
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