Sedimentary Rocks Facts

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1 Sedimentary Rocks Facts Sedimentary Rocks Facts Rocks on Earth are often broken down by the process of weathering. These broken particles, called sediments, are carried away by streams and rivers. When these particles collect and become compacted together over time, they stick together and form a larger structure. These larger structures are referred to as sedimentary rocks. Interesting Sedimentary Rocks Facts: Sedimentary rocks are extremely important resources that give us clues about the Earth's past. Sedimentary rock has layers of sediments that are arranged according to their density. Compaction is the process by which sediments form sedimentary rock. The process by which sediments harden to form sedimentary rock is called lithification. Fossils of organisms become buried over time and are often found in sedimentary rock. Sedimentary rocks are divided among three different groups based on their composition and texture. Classic sedimentary rock forms when older rocks break down and become compacted together. Examples of classic sedimentary rock include sand-stone and breccia. Sand-stone is a sedimentary rock that has been used to make housewares since prehistoric times. Organic sedimentary rock has a high amount of organic material and can be used as a source of petroleum and tar. Examples of organic sedimentary rock include limestone and coal. Chemical sedimentary rock forms when minerals come out of a solution and crystallize. The majority of chemical sedimentary rock comes from minerals left behind by evaporated water. An example of chemical sedimentary rock includes halite which is also known as table salt.

2 Igneous Rocks Facts Igneous Rocks Facts Rocks are classified by the way they form. Igneous rocks are those that form when magma cools and hardens. This process can occur on the Earth's surface or underground. The exact location of the formation of the rock determines the type of igneous rock it is. Interesting Igneous Rocks Facts: When magma rises to the surface of the Earth and hardens, it forms extrusive igneous rock. Extrusive igneous rock tends to be glassy in texture because their formation occurs very rapidly. Examples of extrusive igneous rock include pumice and basalt. Pumice is an extrusive igneous rock used in many products such as toothpaste, cement, and cosmetic products Basalt is an extrusive igneous rock used in constructing buildings and statues. Extrusive rocks are also referred as volcanic rocks because volcanoes are important in their formation. When magma cools and hardens below the Earth's surface, an intrusive igneous rock forms. Because the process of the formation of intrusive igneous rock occurs slowly, these rocks tend to have a grainy texture. Examples of intrusive igneous rock include granite and gabbro. Granite is an intrusive igneous rock used as for making gravestones, statues, and countertops because it is very durable. Gabbro is an intrusive igneous rock that often contains profitable amounts of gold, chromium, and silver. Plutons are bodies of intrusive rock which are usually composed of granite. When intrusive rocks form huge bodies such as those found in the core of mountains, they are referred to as batholiths. Ninety-five percent of the Earth's crust is made of igneous rock. There are over 700 different kinds of igneous rocks that have been identified.

3 Metamorphic Rocks Facts Metamorphic Rocks Facts Rocks are made up of one or more minerals. Although different rocks can contain the same minerals, they are classified based on the way in which they were formed. Metamorphic rocks form when existing rocks are exposed to heat and pressure deep within the Earth's surface. Interesting Metamorphic Rocks Facts: Marble and slate are examples of metamorphic rock. Metamorphic rock is formed under extreme pressure combined with heat over time. Metamorphic rocks are so called because they always begin as another type of rock. When slate forms, some of the clay from the original rock is replaced by the mineral mica. Metamorphic rock can originate not only as igneous and sedimentary rock but also other types of metamorphic rock. During contact metamorphism, broken down pieces of rock near the Earth's surface is altered by magma. During regional metamorphism, rocks buried deep within the Earth are altered by magma chambers. Foliated rocks are types of metamorphic rock that have parallel bands of grain. Non-foliated rocks are types of metamorphic rock that have no arrangement or bands of grain. Marble is a type of metamorphic rock that originates from limestone. Schist is a type of metamorphic rock that can originate from slate which is another type of metamorphic rock. The word metamorphic literally means "changed form". Slate, a metamorphic rock, can form from shale, clay or mudstone. The Taj Mahal in India is made entirely of different types of marble, a metamorphic rock. Serpentine is a type of metamorphic rock that originates as the igneous rock periodite.

4 What is a Fossil? Fossil Facts and Information A fossil is the preserved remains or trace of a plant or animal from the past. That's the simple answer to "what is a fossil?" Plants can be preserved with a carbon film on a piece of shale, an animal bone can be naturally replaced by minerals and preserved, or a footprint in the sand can harden into a fossil. A couple things to know about fossils: Fossils usually only form in sedimentary rock. Sediments have to accumulate over the organism in order to preserve it. This could be a rapid burial, such as a volcanic eruption or mudslide, it could be sap from a tree oozing over an insect, or simply a slow sediment accumulation on the bottom of a lake. Most fossils are marine in origin, or are land animals that fell into a water environment. This is because sediments easily accumulate in water environments (lakes, streams, oceans). Land environments are usually the sites for erosion, not sediment deposition. Image of a few Ammonite Fossils. These are the mineralized shells of marine animals, similar to todays Nautiloids. Let's answer the question "what is a fossil" in a little more detail by going into a specific example about fossils Think about someone finding a Native American arrowhead in a recently ploughed farm field. That plough disturbed and dug up a few inches of soil. The arrowhead, which was previously buried in the soil popped to the surface. How did that arrowhead end up underground in the first place? A Native American left it on the surface hundreds of years ago. Over time, vegetation grew and died, creating soil. The soil slowly accumulated and buried the arrowhead. This is similar to how a fossil forms. Let's take that lost arrowhead above and replace it by a leaf. Lets say the leaf falls into a lake with a low oxygen content, so it does not rot away. Now, let it sit there for a year. It will be covered by a small amount of sediment. Another year goes by and more sediment covers it. Now, multiply the time frame by an unimaginable number of years.. millions of years. Instead of the leaf being buried by a few inches of sediment, it is buried by miles and miles of sediment! Something now begins to happen to that sediment. Under miles and miles of pressure it heats up, the leaf literally cooks. Only the carbon ash remains. Chemical processes start to occur under the tremendous pressure, and the sediments compact into a type of rock... sedimentary rock. Now, add millions of more years, and change the geologic context. Geologic forces thrust that sedimentary rock onto the surface. Wind and weather take its toll. The sedimentary rock outcropping begins to erode away. In one of the pieces of the eroded rock outcropping falls a fossil leaf impression, a preserved carbon footprint of that leaf that fell in the lake millions upon millions of years ago. This is how fossils form. Preservation methods for fossils vary. Plants are fragile and often cook so that the carbon only remains. Animal bones and hard shelled animals are harder, and often have minerals leaching into them replacing the original bone. Sometimes volcanic ash layers cover the plants or animals and preserve them.

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