The term “igneous” is the Latin word for fire. Igneous rocks form when hot liquid rock, called...
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The term “igneous” is the Latin word for fire. Igneous rocks form when hot liquid rock, called magma, cools and solidifies. The type of igneous rock that
The term igneous is the Latin word for fire. Igneous rocks form
when hot liquid rock, called magma, cools and solidifies. The type
of igneous rock that forms depends upon the composition of the
magma and the time it takes to cool.
Slide 2
Igneous rock can form in one of three ways: When rock is heated
to the point that it melts When pressure is released When rock
changes its composition Magma freezes or solidifies around 1,000 0
C (1,800 0 F)
Slide 3
Change in Pressure When you remove the radiator cap from an
over-heated car, the liquid water immediately changes to steam. By
the same process, when pressure on very hot solid rock is released,
it changes into a liquid. Pressure can be released as the rock
approaches the earths surface, or when a fissure or other opening
occurs.
Slide 4
Changes in Composition If fluids, such as water, combine with
very hot rock, it may lower the melting point, allowing the solid
rock to liquefy. This is the opposite of adding salt to ice cream
mix to make it freeze.
Slide 5
Classification of Igneous Rocks
Slide 6
Felsic rocks are: Light-colored due to presence of quartz and
feldspar Rich in silica (65%), aluminum, potassium, and sodium
Began cooling at low temperatures May be intrusive or extrusive
Coarse-grained: granite Fine-grained: rhyolite
Slide 7
granite On the right is coarse-grained granite rhyolite On the
left is fine-grained rhyolite Grain size is due to cooling time;
fast cooling results in fine grains, slow cooling results in larger
crystals. Granite is an intrusive felsic igneous rock Rhyolite is
an extrusive felsic igneous rock
Slide 8
Mafic rocks are: Dark-colored due to iron, magnesium Rich in
calcium, iron, magnesium Began forming at high temps. May be
intrusive or extrusive Coarse-grained: gabbro Fine-grained:
basalt
Basalt, a fine-grained, mafic igneous rock. Note the variation
in in color: the dark area is typical basalt, while the lighter
areas have undergone chemical reactions with air and water.
Slide 11
Gabbro, a coarse-grained mafic igneous rock
Slide 12
Obsidian is extrusive igneous rock that has cooled so quickly
that no crystals can form. Is it Mafic or Felsic?
Slide 13
IntrusivePlutons Intrusive igneous rock formations are called
Plutons; there are several different types: Batholiths Batholiths
are the largest bodies of magma deposits- these measure at least 40
square miles or more for their upper surface, but can be as large
as 15,000 square miles, about the size of Maryland and Connecticut
combined
Slide 14
Halfdome in Yosemite National Park This is part of an exposed
batholith
Slide 15
stock A stock is smaller than a batholith and typically
represents the subsurface passage that fed molten material to a
volcano or field of volcanoes over time. Sillsdikes Sills and dikes
are layers of igneous rock that typically form along fault zones,
fractures, or between and parallel to sedimentary layers.
Slide 16
Dome Mountains are formed from hot molten material (magma)
rising from the Earth's mantle into the crust that pushes overlying
sedimentary rock layers upward to form a "dome" shape. Unlike a
volcano, the magma typically does not reach the Earth's surface.
Instead, the magma cools underneath the surface and forms the core
of the mountains. Navajo Mt.
Slide 17
Note the dark intrusion of igneous rock in the lighter
sedimentary rock. Is this a dike or a sill? Is this felsic or mafic
igneous rock? Which rock type was there first? If this is an
intrusive rock type, why is it now exposed?
Slide 18
Shiprock, New Mexico volcanic neck Shiprock is a volcanic neck
Note the exposed dike
Slide 19
Extrusive igneous formations are created by lava flows, which
can take many forms and produce a wide variety of rock
formations.
Slide 20
Capitol Reef National Park, Utah Note the large, dark areas of
igneous rock.
Slide 21
Pillow Lava
Slide 22
Lava tube in Hawaii
Slide 23
Lava tube cave near Flagstaff, Arizona Formed about 700,000
years ago
Slide 24
Sunset Crater National Monument, near Flagstaff, AZ
Slide 25
Giants Causeway in Ireland. How did this form? What type of
rock is it formed of?