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1 Page #: Igneous Rock Notes Magma and lava form very different types of igneous rocks. Igneous rocks form from molten rock, but where does molten rock come from? The temperature inside Earth with depth. That is, the farther down you go, the it gets. Deep within earth, temperatures are hot enough (1400 F to 2300 F) to melt rock. This molten rock is called. Molten rock that reaches Earth s surface is called. An igneous rock is classified on the basis of its mineral and the size of its mineral. A rock formed from magma can have the same composition as a rock that forms from lava. The rocks, though, will have different names, because the of their will be very different. Check your Notes: What are the two major properties used to classify igneous rocks? Origin of Igneous Rocks Depending on where they form, igneous rocks are classified as or. An intrusive igneous rock is one that forms when magma cools Earth. An extrusive igneous rock is one that forms when lava cools Earth s surface.

2 Granite is a common rock. If magma with the same composition as granite reaches the surface, it forms rocks such as rhyolite and pumice. Basalt is an igneous rock that forms on the ocean floor. Gabbro is an intrusive rock that has the same composition as basalt. You can see extrusive igneous rocks at Earth s surface. But intrusive rocks form within Earth. How do they reach the surface? Forces Earth can push rocks up, as when mountains form. Also, water and wind ( ) break apart and carry away (deposition) surface rocks. Then deeper rocks are uncovered at the surface. What is the main difference between intrusive and extrusive igneous rocks? How are gabbro and basalt similar? How are they different? Textures of Igneous Rocks The of an igneous rock that is, the size of its mineral crystals depends on how quickly magma or lava to form it. In an icemaker, crystals form as water freezes into ice. In a similar way, mineral crystals form as molten rock freezes into solid rock.

3 The magma that forms intrusive igneous rocks stays the surface of Earth. Large crystals can form in intrusive rocks because o The of the Earth is very hot o The high temperatures allow magma to cool o Slow cooling allows time for crystals to form The lava that forms extrusive igneous rocks Earth s surface. Very crystals form in extrusive igneous rocks because o The surface of Earth is than Earth s interior. o The lower temperatures cause the lava to cool o There is for large minerals to form Some igneous rocks contain crystals of very sizes. These rocks formed from magma that started to cool within Earth and then erupted onto the surface. The large crystals grew as the magma cooled. The small crystals grew as the cooled quickly. How does an igneous rock that has both large and small crystals form?

4 Composition of Igneous Rocks is not enough to identify an igneous rock. Think about substances that have similar textures, such as sugar and salt. A spoonful of sugar and a spoonful of salt both consist of small white grains. However sugar and salt are different materials that is, they have different. Likewise, different igneous rocks might have similar textures. To identify them, you have to also consider their. Most igneous rocks are mainly made up of minerals. The silicate mineral group is the most common group in Earth s crust. Silicate minerals contain varying amounts of silica, a compound of and. After identifying the texture of an igneous rock, geologists classify the rock on the basis of how it is in. Special equipment must be used to determine a rock s exact composition, but you can estimate the level of silica in an igneous rock by looking at its. Igneous rocks with levels of silica, such as granite and rhyolite, are typically in color. Those with levels of silica, such as gabbro and basalt, are typically in color. Would you expect a light gray igneous rock to be rich or poor in silica?

5 Igneous rocks make long- lasting landforms. Intrusive Rock Formations Ship rock, in the New Mexican desert, actually formed about one below the surface of the Earth million years ago. It is all that remains of magma that once fed a volcano. The magma cooled and formed igneous rock. As magma pushes toward Earth s surface, it makes channels and other formations underground. Formations of intrusive igneous rock can be and than other types of rock. Why can intrusive igneous rocks be left behind when surrounding rocks are worn away? Extrusive Rock Formations When magma makes its way to Earth s surface through a volcano or crack, the lava may in different ways. Some lava can build huge when it erupts from long cracks in the Earth s surface. Lava that is in silica, such as basalt lava, flows and spreads out in thin sheets over great distances. When lava that is low in silica erupts at a single point, it can build up a huge volcano with sloping sides. The Hawaiian Islands are a chain of volcanoes that are built out of basalt lava. The volcanoes

6 started erupting on the and over a very long time, grew tall enough to rise above the surface of the ocean as islands. Lava that contains a amount of silica does not flow easily. Silica- rich lave tends to build cone- shaped volcanoes with sides. Volcanoes fed by silica- rich magma ten to erupt. The magma is so thick and sticky that pressure can build up until they explode. For example, Mt. St Helens in the state of Washington. Its 1980 eruption the volcano s height by 1300 feet. Lava flows are now adding new extrusive igneous rock. At the current rate, it will take more than 200 years for the volcano to reach its pre height. Why does silica- rich lava tend to build steep volcanoes instead of spreading out?

2 Igneous Rock. How do igneous rocks form? What factors affect the texture of igneous rock? BEFORE YOU READ. Rocks: Mineral Mixtures

2 Igneous Rock. How do igneous rocks form? What factors affect the texture of igneous rock? BEFORE YOU READ. Rocks: Mineral Mixtures CHAPTER 2 2 Igneous Rock SECTION Rocks: Mineral Mixtures BEFORE YOU READ After you read this section, you should be able to answer these questions: How do igneous rocks form? What factors affect the texture