1. Rocks II.Igneous rocks form from molten rock A.Magma and lava form different types of igneous rocks 1.Rock has to get between 750-1250 degrees C to melt That’s 1,400-2,500 degrees F 2.Igneous rock is classified by what minerals are in it and the size of the crystals

2. Rocks 3.Origin of igneous rocks a.Intrusive igneous rock- Forms from magma underground b.Extrusive igneous rock- Forms from lava above ground c.Granite is a common intrusive, but if that magma reaches the surface it is called rhyolite or pumice d.Gabbro is intrusive, but if it’s magma reaches the surface it forms basalt e.How do intrusive become extrusive? 1)Forces inside the earth push rock up to form mountains 2)Wind and water break down and carry away surface rocks 3)The deeper rocks are uncovered

3. Rocks 4.Textures of igneous rocks a.The texture is determined by the size of the crystals 1)This is determined by how fast the rock cools b.Large crystals form in intrusive 1)Interior of the earth is very hot 2)High temperatures allow the magma to cool slowly 3)Slow cooling allows more time for crystals to form, yielding large crystal c.Small crystals form in extrusive 1)The surface of the earth is cooler than the interior 2)Lower temperatures cause lava to cool quickly 3)Not enough time for large crystals to form d.If there are large and small crystals, the large ones formed under the surface and were probably erupted and allowed to finish cooling quickly forming the small crystals

4. Rocks 5.Composition of igneous rocks a.Like sugar and salt crystals the texture of igneous rocks are not enough to identify them b.In the silicate mineral group the amount of silica helps determine the type of rock c.The amount of silica affects the color of the rock 1)The more silica the lighter the color 2)Less silica means darker color

5. B.Igneous rocks make long-lasting landforms 1.Intrusive rock formations a.As channels are made under ground the magma that fills them and cools is often harder than the rock around them b.As erosion takes place the harder rock remains as the softer rock is worn and transported away 2.Extrusive rock formations a.Lava can form large plateaus when it comes out of large cracks in the ground b.It can form mountains after consistent eruptions, from a hot spot, over long periods of time c.Lava with low concentrations of silica travels a long distance before cooling enough to stop flowing – Shield volcano d.Lava with high concentrations of silica does not travel far before cooling – Composite volcano (more explosive eruptions) Minerals