CHAPTER 4
ROCKS
CHAPTER 4
ROCKS
6
Classifying Igneous RocksIgneous rocks are classified by their TEXTURE and their COMPOSITION
TEXTUREINTRUSIVE IGNEOUS ROCKS (Plutonic)
rocks that form below the surface
slowly cooled magma produces individual mineral grains that are large
enough to see
surrounded by layers of Earth-heat cannot escape
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??
EXTRUSIVE
INTRUSIVE
EXTRUSIVE
INTRUSIVE
EXTRUSIVE
Obsidian
Granite
Scoria
Pumice
Diorite
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 RocksCOMPOSITION
type of magma or lava
BASALTIC ROCKS (Mafic)dense dark colored very fluidhigh amount of magnesium & iron
found in the volcanoes of Hawaiilow gas content
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 rockscan have violent eruptions
or quiet eruptionsmedium silica contentmedium thickness
many volcanoes around the Pacific Ring of Fire contain
andesitic magma
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