What are rocks? - Rocks are combinations of minerals stuck together. - Minerals (Rice Krispies) - Rocks (Rice Krispies Treats)

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1 Rocks What are rocks? - Rocks are combinations of minerals stuck together. - Minerals (Rice Krispies) - Rocks (Rice Krispies Treats) Igneous Rocks Think of minerals as ingredients If you have different minerals, you have different rocks. 1

2 Igneous Rocks There are many different types of rocks All rocks are classified based on how and what they are made of. - Like potatoes: mashed, backed, scalloped, etc. - Each come from a plain potato, but were made differently Igneous Rocks Just like there are different types of potatoes, there are different types of rocks The three main types of rocks are: 1. Igneous: : made from cooled lava or magma. 2. Metamorphic: : rocks change under high heat and pressure. 3. Sedimentary: when sediment is squeezed together. 2

3 Igneous Rocks Igneous rocks form when magma or lava cools and hardens. - Magma: inside Earth - Lava: outside Earth Igneous rocks are classified according to: - Where they are made. - The texture of the rock. - What they are made of. Igneous Rocks: Where they are made? Igneous rocks can form inside Earth or outside Earth. Inside Earth: INTRUSIVE IGNEOUS ROCKS - In In side earth. - Think about the interior interior of your car. - Think about an interior interior designer. - What cools? Magma or Lava? Outside Earth: EXTRUSIVE IGNEOUS ROCKS - Ex Ex it something means to go out out of it. - Think about the exterior exterior of your house. - What cools? Magma or Lava 3

4 Igneous Rocks: Where they are made? Igneous Rocks: Texture of the Rocks? Igneous rocks have different textures. - Texture is how a rock looks and feels. - Texture is based on the size of crystal grains in the rock. - Sometimes they are large, sometimes small. 4

5 Igneous Rocks: Texture of the Rocks? Igneous Rocks: Types of Textures Pegmatite: Very large crystal grains They are so big that some even join together to become big You can see them with your eyes Ex: Pegmatite Coarse-grained: Large crystal grains You can see them with your eyes Ex: Granite Fine-grained: Small crystal grains Too small to be seen with your eyes you need a microsco Ex: Basalt Glassy/Volcanic Glass: No crystals at all Ex: Obsidian or Pumice 5

6 Igneous Rocks: Types of Textures Rate of Cooling Porphyry: Porphyry is when you have a mix of large and small crystal grains. Think of the word potpourri that that s a collection of things. ( big and small crystals) What could have caused this? How do we get big crystals? slow cooling inside Earth How do we get small crystals? quick cooling outside Earth This rock experienced two cooling situations. Igneous Rocks: Texture of the Rocks? 6

7 Igneous Rocks: Types of Textures Rate of Cooling Pegmatite and coarse-grained textures have very large crystals. - The slower the magma cools, the larger the mineral crystals. - Rocks that cool slowly have larger crystals. SLOW COOLING = LARGE CRYSTALS Ex: Let s say you are trying to cool a cake you made. Instead of putting it outside to cool, you turn the oven off and keep it in there to cool. You won t be able to eat the cake for awhile because it will take longer to cool since it is in the hot oven. Ex: Say you are a farmer. You plant your crops in spring and let them grow for many months until fall. The crops will be big because they had lots of time to grow before the ground froze. Igneous Rocks: Types of Textures Rate of Cooling Fine grained texture means that there are very tiny crystal grains. - The faster the magma cools, the smaller the mineral crystals. - Rocks that cool fast have small crystals. FAST COOLING = SMALL CRYSTALS Ex: Back to the cake, let s say you put it in the fridge to cool. It will certainly cool faster because of the cooler temperatures. Ex: Back to the crops. Instead of letting the crops grow all summer, you harvest them early. They won t get to grow as big because they didn t have enough time. 7

8 Igneous Rocks: Types of Textures Rate of Cooling Igneous Rocks: Types of Textures Rate of Cooling SUMMARY: Intrusive Rocks: Form inside the Earth where it is hot, so the magma cools slowly producing large crystals. Extrusive Rocks: Form outside of the Earth where it is cool, so the lava cools quickly producing small or no crystals. 8

9 Igneous Rocks: Texture of the Rocks? Igneous Rocks: Magma Types Granitic - Lots of silica,, low Fe -Therefore it will be light in color. Andesitic -Medium amounts of Si/Fe - Not light, but not dark Basaltic - Lots of Fe,, low Si - Very dark in color 9

10 Igneous Rocks: Magma Types Let s s say you make batter. You take that batter and pour it in a pan and you make round, flat pancakes. You take that batter and pour it into a waffle iron and make thick waffles. The same batter makes two completely different items based on the e way it was made. This is just like magma when magma cools fast, you get one type of rock. When it cools slow, you get a completely different type of rock. Ex: Granitic magma forms granite and rhyolite when it cools differently. 10

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