Download Rocks and Minerals 2 Igneous

What is a Rock?
• A rock is a:
–Naturally formed,
–Consolidated material,
–Composed of grains of one
or more minerals.
Some Rocks
Types of Common
Rocks
• There are three types of
common rocks:
–Igneous rock
–Sedimentary rock
–Metamorphic rock
Igneous Rock
• Igneous rocks form from
the solidification of
magma.
–Ex: pumice, obsidian
Identifying Igneous Rocks
• Where the igneous rock forms in the
crust shapes their composition so
igneous rocks are identified by their
texture.
–Extrusive rocks form at or near the
surface and are fine-grained.
–Intrusive rocks form below the
surface and are coarse-grained.
Basalt: Igneous –
Extrusive, Fine-grained
Granite: Igneous – Intrusive,
Coarse-grained
Igneous Rock Features: Felsic
• Felsic rocks are rich in potassium
feldspar and quartz and are light in
color.
– Example is the granite family of rocks.
• Felsic rocks are most common in the
continents.
Felsic Igneous Rocks
Igneous Rock Features: Mafic
• Mafic rocks are rich in dark
plagioclase feldspar and pyroxene.
– Example the gabbro family of rocks.
• Mafic rocks are more common in the
ocean basins.
Mafic Igneous Rocks
Basalt
Igneous Identification
• Some igneous rocks have holes in
them that formed during the cooling
of the magma. These types are said
to be vesicular.
Igneous Rocks
Structure of Igneous Rocks
• Shield and Cinder Cone volcanoes will
erupt and create lava flows, and lava
plateaus, that form igneous rocks.
• When magma does not erupt but instead
forces its way up through cracks and
faults it produces large masses of
intrusive rock called plutons.
Shield (Etna) and Cinder Cone (Paracutin)
Plutons
• Plutons are classified according to size:
• Sills are slabs of igneous rock parallel to the
rocks they intrude;
• Dikes are slabs of igneous rock that cut across
the rock layers they intrude;
• A laccollith forms between two rock layers,
bulging up to form a dome;
• A batholith is the largest intrusion and they
form the core of many mountain ranges.
• When a volcano erodes the harder volcanic
neck is often left behind.
Devil’s Tower
is the result of
igneous rock
that was
underground
until all the
weaker
surrounding
rock was
eroded