Chapter 3 rocks

Rocks: Materials of
the Solid Earth
Chapter 2
Earth Science, 6e
Modified by Dr. Kane


What is a Rock?
How would you define a rock and a
mineral?


What types of Rocks are there?
Igneous Rocks: from magma or lava
Origin: igneous activity
• Example: granite or basalt

Sedimentary rocks: from sediments
Origin: weathering and erosion
Example: sandstone or clay

Metamorphic rocks: from stress
Origin: mountain building
Example: gneiss or marble


The rock cycle (page 45)


PART – I: IGNEOUS ROCKS
FEEDBACK:

From what process igneous rocks from?


Plate Margins
• Divergent: Plates pull apart
Example: Mid ocean ridge; Rift
• Convergent: Plate come together
– Ocean – Continent; Ex: Cascades, Andes
– Ocean – Ocean; Ex: Japan, Caribbean
– Continent – Continent; Himalaya

• Transform Fault: Plates slide


Origin of Magma (page 228)
Magma forms at three major geological
settings:
• Divergent (Ex: Mid ocean ridge)
• Convergent (Ex: Cascades volcanoes)
• Intra plate Not a plate margin (Ex: Hawaii,
Hot spot)


Origin of Magma (page 148)


Mid Ocean Ridge (divergent)


Subduction Zone (Convergent)

Causes of Magma Formation
Decompression Melting (opening a bottle of
soda)

Factors influencing magma formation:

1. Heat Increase
2. Reduction of confining Pressure
Role of volatiles (gases)


Types of Igneous rocks
 Magma cools and crystallizes
Inside the crust → Plutonic or Intrusive rocks

Lava cools and crystallizes
Outside the crust → volcanic or extrusive rocks


Classification of Igneous rocks
 When identifying Igneous rocks look
for:
1. Grain Size (TEXTURE)
and

1. Rock color (CHEMICAL COMPOSITION)

Rate of Cooling and Crystal Size
• Texture is size and arrangement of crystals

• Crystal size is determined by the rate and
depth of cooling of magma/lava
• Slow rate forms large crystals
• Fast rate forms microscopic crystals
• Very fast rate forms glass


Feedback:

The slower the rate
of cooling, the
smaller / larger the
crystals?


Types of Textures
Phaneritic: Coarse grain/slow cooling rate
Example: Granite or Diorite
Aphanitic: Fine grain/fast cooling rate
Example: basalt or rhyolite
Glassy: glasslike/very fast cooling rate
Example: Obsidian (volcanic rock)


Types of Textures
Porphyritic: Slow then rapid cooling
Example: porphyry basalt, porphyry granite

Vesicular: Full of holes due to gases
Example: Vesicular basalt, scoria, and pumice

Pyroclastic: Angular volcanic fragments
cemented by ash from violent eruptions
Example: tuff


Photomicrograph


Photomicrograph


What’s the texture?


What’s the texture?


What’s the texture?


What’s the texture?


What’s the texture?

Obsidian Aztec