Download Chapter 6.2: Igneous Rocks

CHAPTER 64
CHAPTER 4
ROCKS
ROCKS
Classifying Igneous Rocks
Igneous rocks are classified by their
TEXTURE and their COMPOSITION
TEXTURE
INTRUSIVE IGNEOUS ROCKS (Plutonic)
rocks that form below the surface
surrounded by layers of Earthheat cannot escape
slowly cooled magma produces
individual mineral grains that are large
enough to see
EXTRUSIVE IGNEOUS ROCKS
(Volcanic)
rocks that form from lava
above the surface
lava is exposed to air and water
magma cools quickly producing fine
grained rocks (cannot see mineral
grains)
atoms do not have time to arrange
themselves in repeating patterns
INTRUSIVE OR EXTRUSIVE??
Pumice
Obsidian
Scoria
EXTRUSIVE
EXTRUSIVE
EXTRUSIVE
Granite
INTRUSIVE
Diorite
INTRUSIVE
Porphyry
• A mixture of large and small crystals
• Magma rises slowly through the crust
before erupting to the surface
– Within the crust, large crystals can grow
– On the surface, cooling stops any more
crystals from growing
Vesicular
• Refers to vesicles (holes, pores, or
cavities) within the igneous rock.
• Vesicles are the result of gas expansion
(bubbles), which often occurs during
volcanic eruptions.
• Pumice and scoria are common types of
vesicular rocks.
Classifying Igneous Rocks
COMPOSITION
type of magma or lava
BASALTIC ROCKS (Mafic)
dense
dark colored very fluid
high amount of magnesium & iron
low gas content
found in the volcanoes of Hawaii
How does this explain the black
sand beaches of Hawaii?
GRANITIC ROCKS
(Felsic/Intermediate)
lower-density
light colored
thick & stiff magma
high amount of silica & oxygen
contains a lot of gas causing very
explosive eruptions
ANDESETIC ROCKS (Dioritic)
mineral composition between that
of basaltic and granitic rocks
can have violent eruptions
or quiet eruptions
medium silica content
medium thickness
many volcanoes around the
Pacific Ring of Fire contain
andesitic magma