Igneous Rocks

Igneous rocks form from volcanoes Igneous rocks form from volcanoes. They can either form from melted rock deep underground known as magma or melted rock on the surface of the earth known as lava. Why does the magma rise to the surface? It’s a liquid so it is less dense.

There are 2 main groups of igneous rocks. Rocks that form from lava are known as extrusive. They form on the surface of the earth. Rocks that form from magma are known as intrusive. They form deep underground. IN trusive

Intrusive rocks cool underground. Do they cool quickly or slowly? Extrusive rocks cool on the surface of the Earth. Do you think they cool quickly or slowly? Quickly Intrusive rocks cool underground. Do they cool quickly or slowly? Slowly

Igneous Rocks are made up of crystals. What do you think happens to the size of the crystals when they have a long time to grow? They grow big. Which type of igneous rock do you think has the bigger crystals, intrusive or extrusive? Intrusive – it takes longer to cool.

A lava flow on the surface. Extrusive rocks are forming!!

I guess this road will be closed for awhile!

GRANITE SLOWLY An intrusive igneous rock. Granite has big crystals because it cooled SLOWLY

An extrusive igneous rock BASALT An extrusive igneous rock Basalt has very small crystals because it cooled QUICKLY

OBSIDIAN Still an extrusive igneous rock This rock cooled really fast!

Let’s Review

Igneous Rock Chart

Intrusive Igneous Rocks

Intrusive Igneous Rock with Large Crystals

Granite

Extrusive Igneous Rocks

Basalt

Compare Intrusive Rocks to Extrusive Rocks: Small Crystals Extrusive Large Crystals Intrusive

Obsidian – NO crystals! Glassy texture

Slow or fast cooling? Large crystal, therefore slow cooling!

How to Identify Igneous Rocks…

1. Color/Density Felsic – light colored, low density Mafic – dark colored, high density

2. Texture Large crystals Small crystals No crystals (obsidian) Coarse-grained – Fine-Grained – Glassy – Vesicular – Small crystals No crystals (obsidian) Gas pockets

Vesicular Texture Example = Pumice Gas Pockets

Pumice

Minerals found in Granite

Minerals found in granite.

Igneous Questions

Classify the following rocks as either: volcanic or plutonic and mafic or felsic a b Volcanic and mafic Plutonic and mafic c d Volcanic and felsic Plutonic and felsic

Name the minerals found in Rhyolite

Name the minerals found in Basalt

Q: Name an extrusive igneous rock with a fine texture.

Q: Name an extrusive igneous rock with a fine texture and a felsic composition

Q: Name an intrusive igneous rock with a coarse texture and a mafic composition

Q: Name the minerals found in Granite.

Q: Name the minerals found in mafic rocks.

Q: Name the minerals found in Andesite.

Name the ELEMENTS found in Mafic rocks. Fe = Iron Mg = Magnesium

Name the ELEMENTS found in Felsic Rocks Al = Aluminum

Why is it unlikely to find Fossils in Igneous Rocks? Fossils cannot survive the heat from the lava and magma and are destroyed on contact.