1. Introduction to Rocks
Chapter 5
Earth Science 11

2. What is a Rock? What do you think a rock is?
A group of minerals bound together some way
Example: lava hardens into rocks, sand and clay harden into rocklike materials

3. Types of rocks Igneous Rocks Sedimentary Rocks Metamorphic Rocks
Formed by the cooling and hardening of hot molten rock from inside Earth (magma)
Formed by hardening and cementing of layers of sediments. May consist of rock fragments, plant and animal remains.
Formed when rocks that already exist are changed by heat and pressure.

4. Types of Igneous Rocks 1. Plutonic (Intrusive)
Formed underground from cooled magma
Has distinct mineral grains
Plutonic rocks are seen at the surface, after the rocks covering them are worn away.
Granite exposed by weathering

5. Types of Igneous Rock 2. Volcanic (Extrusive)
Formed from magma that pours onto Earth’s surface during volcanic eruptions (lava).
May also be formed out of volcanic dust or ash.
Lack distinct mineral grains.

6. Plutonic vs. Volcanic Plutonic with distinct mineral grains Gabbro
Volcanic that lacks distinct mineral grains Basalt

7. Types of Magma 1. High-Silica (felsic) Thick and slow flowing magma
Forms rocks that have light-coloured minerals
Most plutonic rocks are felsic
Granite
Contains light coloured mineral such as quartz and feldspar

8. Types of Magma 2. Low-Silica (mafic) Lower percentage of silica
Hotter, thinner, more fluid, darker-colour
Forms rocks that contains mostly dark minerals
Basalt
Contains dark minerals such as hornblende, augite, and biotite.

9. Textures of Igneous Rock
Rocks are not only group by their mineral composition but by their texture.
Texture depends on:
Size of the crystals
Shape of the crystals
And arrange of its mineral crystals

10. Textures of Igneous Rock
Igneous rock texture ranges from: glassy-smooth coarse-grained Obsidian Granite

11. Textures of Igneous Rock
Crystal size most important factor affecting texture.
Affected by how fast the magma hardens
Magma within the crust hardens slowly = larger crystals
Magma on Earth’s surface hardens rapidly = tiny crystals
Very rapid magma harden = no crystal development