Download Chapter 6 Section 2 Notes

Ch. 6.2. Igneous Rocks
1. Intrusive igneous rock: formed from the
cooling and solidification of magma beneath
Earth’s surface
2. Extrusive igneous rock: formed from the
cooling and solidification of lava at Earth’s
surface
The Formation of Magma
• 3 factors influence rock melting:
- temperature
- pressure
- presence of fluids in the rock (such as
water)
Partial Melting
• Minerals with lower melting points are the first
minerals to melt.
• As the temperature increases and as other minerals
melt, the magma’s composition changes.
Chapter 6
The Formation of Magma
Fractional Crystallization
• Minerals that have the highest freezing
points crystallize first.
• When magma cools, the cooling
process is the reverse of the process of
partial melting.
•
Chapter 6
The Formation of rocks
A. Intrusive Igneous Rock Structures
• Batholiths: intrusive formations that spread over
a large area
• Stocks: similar to batholiths but smaller
• Sills: layers of rock parallel to the layers of rock
that surround it.
• Dykes: new layers cutting across existing layers.
B. Extrusive Igneous Rock Structures
– Volcano: a vent through which magma,
gases, or volcanic ash is expelled.
– Lava flows, lava plateaus, and tuff layers
Igneous Rock
Magma
Melting
Partial Melting
Solidifying
Fractional
Crystallization
Texture
Intrusive Extrusive
Textures of Igneous Rocks:
a. Coarse-Grained
• Rocks cooled slowly, have large
mineral crystals
b. Fine-Grained
• rocks cooled fast, have small grains.
c. porphyritic texture: magma cooled
slowly at first, but then cools more
rapidly as the magma nears or reaches
Earth’s surface
– large crystals together with smaller
crystals.
d. vesicular texture
– Contains bubbles of gases
e. glassy texture: highly viscous magma
cooled very rapidly
– No large crystals
Composition of Igneous Rock
1. Felsic Rock:
- rich in feldspars and
silica
- light in color.
• Ex: granite, rhyolite,
obsidian, and pumice.
2. Mafic Rock
- rich in magnesium and iron,
dark in color.
• Example: basalt and gabbro.
3. Intermediate Rocks:
• proportions of silica between
felsic and mafic.
• Examples: diorite and
andesite.
Intrusive vs. extrusive igneous rock