4-2 Igneous Rocks forms when molten/melted rock (magma or lava) cools and hardens (solidifies)

“How do igneous rocks form?” Examine samples of granite and obsidian What is the texture of each? Coarse, fine, glassy Which one is NOT made of crystals? Both are igneous rocks, made of similar minerals. What can you infer about how/where each were formed? Granite Obsidian

Igneous Rocks probably first rocks on Earth ignis means “fire” think of “ignite”

Label the lava and magma

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Two Types of igneous rocks 2. Intrusive from magma (coarse-grained)—cool slowly ex: granite most abundant igneous rock makes up much of continental crust forms core of many mountain ranges 1. Extrusive from lava (fine-grained)—cool quickly ex: basalt most common extrusive igneous rock especially common in oceanic crust

{enrich} Igneous rock--mineral composition Mafic forms dark-colored rocks lots of calcium, iron, and magnesium (low in silicon) ex: basalt Felsic forms light-colored rocks less dense lots of aluminum, potassium, silicon, and sodium ex: granite

Make a Double Bubble or a Venn Diagram Basalt compared to Granite (see Brainpop) Include: intrusive/extrusive, coarse/fine grained, minerals that make it up, color, dark or light-colored, and silica content see handout for help

Questions: What is the most common igneous rock? granite Why does PUMICE float in water? It came from an explosive volcano, so it had a lot of trapped air bubbles (so density less than 1) Why does lava cool more quickly than magma? exposed to the air or water

Questions: What determines the texture of an igneous rock? >>how fast the lava/magma cools (and if the volcano is explosive) A batholith forms from a large magma chamber that slowly cools deep beneath the earth’s surface. What type of texture is this igneous rock formation most likely to have? >>coarse-grained

PERFORMANCE TASK #3