Foliation normally forms when pressure was exerted on a rock from one direction. If pressure is exerted from all directions, then the rock usually does not show foliation. This is an example of contact metamorphism. It is important to note that metamorphism does not cause complete melting of the initial rock. It only causes changes to a rock by heat or pressure. The rearrangement of the mineral crystals is the most common way that we notice these changes.
Table 4. Hornfels, with its alternating bands of dark and light crystals is a good example of how minerals rearrange themselves during metamorphism. The minerals that compose gneiss are the same as granite. Feldspar is the most important mineral that makes up gneiss along with mica and quartz. Gneiss can be formed from a sedimentary rock such as sandstone or shale, or it can be formed from the metamorphism of the igneouse rock grantite.
Gneiss can be used by man as paving and building stone. Non-Foliates are metamorphic rocks that have no cleavage at all. Quartzite and marble are two examples of non-foliates that we are going to study. Quartzite is composed of sandstone that has been metamorphosed. Quartzite is much harder than the parent rock sandstone. It forms from sandstone that has come into contact with deeply buried magmas. Quartzite looks similar to its parent rock.
The best way to tell quartzite from sandstone is to break the rocks. Sandstone will shatter into many individual grains of sand while quartzite will break across the grains. Marble is metamorphosed limestone or dolomite. Both limestone and dolomite have a large concentration of calcium carbonate CaCO3. Marble has many different sizes of crystals.
Marble has many color variances due to the impurities present at formation. Some of the different colors of marble are white, red, black, mottled and banded, gray, pink, and green. Marble is much harder than its parent rock. This allows it to take a polish which makes it a good material for use as a building material, making sink tops, bathtubs, and a carving stone for artists.
Today, headstones are made from marble and granite because both of these rocks weather very slowly and carve well with sharp edges. Write the answers to the following questions in complete sentences on a piece of paper. Write a definition in your own words of what a metamorphic rock is.
What are the three agents of metamorphism? What are the three types of metamorphism? In your own words write a definition of the rock cycle. Skip to main content. Toggle menu Go to search page. Search Field. 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.
Notice how many time "weathering" and "erosion" green arrows appear in the above diagram? When it pours out on Earth's surface, magma is called lava. Yes, the same liquid rock matter that you see coming out of volcanoes. Igneous rock that pours out onto the Earth's surface is called igneous extrusive , whereas igneous rock that cools beneath the surface is called igneous intrusive.
On Earth's surface, wind and water can break rock into pieces weathering! They can also carry rock pieces to another place erosion!. Usually, the rock pieces, called sediments, drop from the wind or water to make a layer. The layer can be buried under other layers of sediments. After a long time the sediments can be cemented together to make sedimentary rock. In this way, igneous rock can become sedimentary rock. All rock can be heated. But where does the heat come from? Inside Earth there is heat from pressure push your hands together very hard and feel the heat.
Rocks have a reputation for being solid, hard, and indestructible. But rocks are always changing! Existing rocks undergo change as outlined in the rock cycle which is similar to the water cycle. Rocks change very slowly under normal activity , but sometimes catastrophic events like a volcanic eruption or a flood can speed up the process. Rocks line river beds and jut above the landscape as mountain peaks; they are fun to collect and sometimes are very beautiful.
Each rock is different; some are smooth and round, some are sharp and dangerous. They come in all colors: pink, green, orange, white, red. And yet, scientists classify them all in only three groups! Keep reading to learn about the three types of rocks and the rock cycle. Igneous rocks are formed when hot magma cools rapidly, either by hitting underground air pockets intrusive igneous rocks or by flowing from the mouth of a volcano as lava on top of the ground extrusive igneous rocks.
Granite, obsidian, basalt, and pumice are all common examples of igneous rocks. Pumice is a very porous rock because when the lava cooled, pockets of air were trapped inside. Because of all those air pockets, pumice can actually float! Sedimentary rocks are formed by layers of sediment dirt, rock particles, etc. Common examples of these rocks are limestone, sandstone, and shale. Sedimentary rocks often have lots of fossils in them because plants and animals get buried in the layers of sediment and turn into stone.
Clastic sedimentary rocks are rocks that people generally think of; rocks that have pieces of other, pre-existing rocks that form a new rock. Metamorphic rocks are a combination of rock types, compressed together by high pressure and high temperatures.
They usually have a more hard, grainy texture than the other two types. Igneous, sedimentary, and metamorphic rocks on the surface of the earth are constantly being broken down by wind and water. Wind carrying sand wears particles off the rock like sandpaper.
Rushing river water, crashing surf, and precipitation all rub off the rough edges of rocks, leaving smooth rocks or pebbles behind.
Water seeps into the cracks in mountain rocks, then freezes, causing the rocks to break open. When the particles are broken off a rock and stay in the same area, it is called weathering.
Eroded rock particles are carried away by wind or by rain, streams, rivers, and oceans. As rivers get deeper or flow into the ocean, their current slows down, and the rock particles mixed with soil sink and become a layer of sediment.
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