1. Earth Science Chapter 3 Section 2
Igneous Rock
Earth Science Chapter 3 Section 2

2. Introduction Igneous rock is sometimes called volcanic rock
Igneous rock forms when magma cools and hardens (crystallizes)

3. Formation of Igneous Rock
Most igneous rock forms from magma deep below the earths surface.
Igneous rocks are classified as either intrusive or extrusive depending on where they form.
Intrusive igneous rock forms below the surface
Extrusive igneous rock form on the surface

4. Composition of Magma Magma is composed of …
silicon
oxygen
aluminum
iron
calcium
sodium
potassium
magnesium
Magma also contains gases which makes it less dense than the surrounding rock. This is why magma rises.

6. Intrusive Igneous Rock (Plutonic)
Intrusive igneous rock tends to have large crystals because the rock formed slowly below the earth’s surface
When an igneous rock forms slowly the mineral crystals have more time to form
Intrusive igneous rock is only visible at the surface when weathering and erosion wear away the rock above.
The most common example on the earth’s surface is granite.

7. Extrusive Igneous Rock (Volcanic)
Magma that reaches the earth’s surface is called lava.
Most of the gases escape when magma reaches the surface.
Extrusive igneous rock are commonly found around volcanoes.
Extrusive igneous rocks tend to have small crystals because the rock formed quickly
The temperature at the surface is much cooler than inside the earth
When an igneous rock forms quickly the mineral crystals do not have time to form
Basalt, pumice, and obsidian are examples of extrusive igneous rock.

9. Classification of Igneous Rock
Texture
Intrusive
Cools slowly below the earth’s surface
Have larger crystals
Coarse grained
granite
Extrusive
Cools quickly at the earth’s surface
Have smaller crystals
Fine grained
May have a glassy appearance when no crystals form when the rock formed very quickly
Obsidian, pumice, basalt

10. Porphyritic Contain a combination of large and small crystals
Form because some minerals crystallize faster than others
Andesite

11. Magma Composition
Magma and lava that are rich in potassium, sodium, and calcium form light colored silicates such as quartz, mica, and feldspar
Magma and lava that contain iron and/or magnesium form dark colored silicates such as olivine and pyroxene.

12. Granitic Composition magma
Light color
Mostly quartz and feldspar
Much of the continental crust
Granitic rocks are sometimes called felsic which is a combination of the words feldspar and silica

13. Basaltic composition magma
Contain mostly magnesium and iron rich dark silicates
Darker in color
Basalt is the most common and makes up most of the ocean floor
Sometimes called mafic which is a combination of the words magnesium and ferrum which is a term for iron.

14. Andesitic composition magma
Igneous rocks with an intermediate composition which is a combination of light and dark minerals
Named for the common volcanic rock andesite