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The crust of Earth is not made up of one piece of rock. It is made up of many plates that float on the surface of Earth. As the plates move around, they cause changes to the land.
When plates collide, mountains rise and volcanoes erupt. When plates scrape and slide past each other, an earthquake occurs.
Layers of Earth Plates Earth Is Made Up Of Four Layers Crust - solid layer of rock pieces; 7-30 miles thick Mantle - thick molten rock that flows like thick oatmeal; about 1,800 miles thick Outer Core - liquid iron and nickel; about 1,300 miles thick Inner Core - solid iron and nickel; about 800 miles thick
Erosion is the process of moving sediment from one place to another. Sediment is tiny pieces of rock, soil, and sand. Erosion carries weathered materials away from a place.
Moving water and rainfall are important in erosion.
Wind and glacier ice are also important because they move sediment from one place to another place. Glaciers cut away the land and carry pebbles, rocks, and even huge boulders to a new spot. For example, Half Dome in Yosemite was cut in half by a glacier.
Deposition is the process of dropping, or depositing, sediment in a new location. Deposition happens when the speed of water decreases or slows down and the sediment drops to the bottom of the water.
An earthquake is the shaking of the ground caused by the sudden release of energy in the Earth’s crust. Earthquakes happen along faults or on the edges of different plates. Faults are breaks in a plate where pieces of rock move. In the ocean, an earthquake can cause a tsunami.
Volcanoes form at plate boundaries. A volcano is a mountain formed by lava and ash. Hot, melted rock called magma comes out of the Earth. When magma reaches the surface of Earth, it is called lava. Lava cools and hardens. When this happens, rock is formed.
Landslides and mudslides cause huge chunks of Earth to move to a new location. This changes the shape of Earth.
Volcanoes, Earthquakes, and Landslides Three Types of Faults Result of an Earthquake Volcano
The word igneous means “from fire”. There are two types of igneous rock. One type is formed inside the earth (below the ground), and the other is formed on the earth’s surface (above the ground).
Magma (melted, molten rock) is deep inside the earth. As magma rises towards the earth’s surface, it cools. When it cools, it can harden and form igneous rock. Because the magma cooled slowly, the rocks often have a coarse texture with large mineral crystals. An example of this kind of igneous rock is granite. This type of igneous rock is formed inside the earth.
If the magma comes onto the surface of the earth, it is called lava. Lava cools on the earth’s surface and hardens to form igneous rock. Because the lava cools quickly, this type of igneous rock has small mineral crystals. This type of rock can have a glassy appearance as in obsidian. Pumice is a lightweight rock because gases bubbled out of the lava as it cooled.
The rock cycle never ends because rocks are always changing from one type of rock to another type of rock.
Rocks are changed due to weathering, erosion, heat that causes melting, pressure, and cementing.
For example, weathering can break pieces off an igneous rock. The pieces called sediment are carried away by erosion. The sediment settles to the bottom of water. Pressure and cementing change sediment into sedimentary rock.
Rocks are made of one or more minerals. A mineral is a non-living (inorganic) solid material that is formed by nature and has a crystal form.
Some minerals are very hard and some are very soft. Hardness is the ability of a material to resist being scratched. A rock's hardness can be determined by its ability to scratch softer materials.
The Mohs Hardness Scale is one way of identifying the hardness of rocks and minerals. To use this scale, the scratch test works great. For example, if the mineral can be scratched with Fluorite but not with Calcite, it has a hardness of about 3.5. Another example--If the mineral can be scratched with Talc, it has a hardness of less than 1. Low numbers on the Mohs Hardness Scale refer to soft minerals and high numbers refer to hard minerals.
Diamond is the hardest of all minerals and can’t be scratched by other minerals except another diamond.
Common things can be used to scratch a rock if the minerals in the scale can’t be found. For example, a fingernail has a hardness of 2.5, a copper penny has a hardness of 3.5, glass has a hardness of 5.5 - 6.
Minerals are also identified by their color, luster, and streak. To describe luster, words like metallic, glassy, pearly, silky, and dull are used.
Click on Oxford Museum of Natural History to see the minerals and common items that are made from the mineral. Just click on the mineral to view the information.