Weathering is all about rocks. To understand weathering, we must first learn about rocks. Rocks are the most common of all materials on earth. They are familiar to everyone. You may recognize rocks in the form of a mountain near your hometown, the gravel in a driveway, the cliffs lining your favorite fishing hole, or the granite or sandstone or limestone your fingers and toes cling to at your favorite climbing area.
Rocks should be considered products of their environment - when their environment changes, so will the ways the rock weathers and erodes, or is otherwise shaped. Rocks form in one of two distinct environments: either below the surface of the earth or at its surface.
Rocks are composed of minerals. Minerals are naturally occurring, inorganic substances, which have an ordered internal structure giving them a specific appearance. Interestingly, ice is a mineral. Some of the more common rock-forming minerals are quartz, feldspar, pyroxene, hornblende, and olivine.
Minerals should not be confused with rocks. For example, granite is a rock. The triad don't you love that word, triad? You can learn about rock types and other things in great detail below. But here's the real important stuff about rocks and rock types that are integral to understanding this module:.
There are three rock types - there are a lot of sedimentary; some granite; and very little metamorphic rocks on the Colorado Plateau The rock cycle happens - how rocks form determines how they will weather Rocks weather differentially - without differential weathering, the landscape would not be as strikingly diverse! In this Module, you will encounter a LOT of sandstone. Sandstone is a sedimentary rock that is highly resistant to weathering.
Other sedimentary rocks you will encounter are mudstone and siltstone. These are soft and easily weathered lots in the Painted Desert. Yet another sedimentary rock you will see is limestone. Limestone is composed of calcium carbonate, which is water soluble it dissolves in water. Therefore, the limestone you find in a dry area will remain a rock a lot longer than limestone you find in a MOIST area. Regarding metamorphic rocks, there really aren't many of these on the Colorado Plateau..
So, good thing for you, we are really not going to cover this rock type in this Module. You will see a few igneous rocks in this Module You see granite intrusive igneous and basalt extrusive igneous.
The granite you will see is high up in the La Sal Mountains and the basalt you will see sits as cap rocks on top of softer, underlying sediments. A cap rock is a comparatively more resistant rock that protects the rocks beneath it from weathering and eroding. The key to understanding rock weathering is to realize that rocks weather at different rates and into different forms based on their chemical composition and based on what weathering processes dominate the area.
For WAY more information on rocks than you are required to know for this Module, visit the following links:. Jump to igneous Jump to metamorphic Jump to sedimentary. Weathering breaking down rock and erosion transporting rock material at or near the earth's surface breaks down rocks into small and smaller pieces.
These smaller pieces of rock such as sand, silt, or mud can be deposited as sediments that, after hardening, or lithifying, become sedimentary rocks.
Extreme pressure from burial, increasing temperature at depth, and a lot of time, can alter any rock type to form a metamorphic rock. If the newly formed metamorphic rock continues to heat, it can eventually melt and become molten magma. When the molten rock cools it forms an igneous rock. Metamorphic rocks can form from either sedimentary or igneous rocks. The sedimentary particles from which a sedimentary rock is formed can be derived from a metamorphic, an igneous, or another sedimentary rock.
All three rock types can be melted to form a magma. Thus, the cycle has continued over the ages, constantly forming new rocks, breaking those down in various ways, and forming still younger rocks. Rocks at the surface of the earth range in age from over three billion years old to a few hundred years old.
Igneous rock can change into sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock. Igneous rock forms when magma cools and makes crystals. Magma is a hot liquid made of melted minerals. The minerals can form crystals when they cool. Igneous rock can form underground, where the magma cools slowly. Or, igneous rock can form above ground, where the magma cools quickly.
Dissolution is a form of weathering—chemical weathering. With this process, water that is slightly acidic slowly wears away stone. These three processes create the raw materials for new, sedimentary rocks.
Precipitation and lithification are processes that build new rocks or minerals. Precipitation is the formation of rocks and minerals from chemicals that precipitate from water.
Finally, lithification is the process by which clay, sand, and other sediments on the bottom of the ocean or other bodies of water are slowly compacted into rocks from the weight of overlying sediments.
Sedimentary rocks can be organized into two categories. The first is detrital rock , which comes from the erosion and accumulation of rock fragments, sediment , or other materials—categorized in total as detritus, or debris.
The other is chemical rock, produced from the dissolution and precipitation of minerals. Detritus can be either organic or inorganic. Organic detrital rocks form when parts of plants and animals decay in the ground, leaving behind biological material that is compressed and becomes rock.
Coal is a sedimentary rock formed over millions of years from compressed plants. Inorganic detrital rocks, on the other hand, are formed from broken up pieces of other rocks, not from living things.
These rocks are often called clastic sedimentary rocks. One of the best-known clastic sedimentary rocks is sandstone. Why do sedimentary rocks have layers? What happens when limestone comes in contact with an acid? Why are sedimentary rocks the only rock type to contain fossils? Why are sedimentary rocks stratified? Why are sedimentary rocks important?
Sedimentary rocks are one of three main types of rocks, along with igneous and metamorphic. Igneous rocks are one of three main types of rocks along with sedimentary and metamorphic , and they include both intrusive and extrusive rocks.
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