Name: _____________________________
Igneous Rocks
How Igneous Rock Is Formed
Igneous rocks are called fire rocks and are
formed either underground or above
ground. Underground, they are formed
when the melted rock, called magma, deep
within the earth becomes trapped in small
pockets. As these pockets of magma cool
slowly underground, the magma becomes
igneous rocks.
Igneous rocks are also formed when
volcanoes erupt, causing the magma to rise
above the earth's surface. When magma
appears above the earth, it is called lava.
Igneous rocks are formed as the lava cools
above ground.
http://sln.fi.edu/fellows/payton/rocks/create/igneous.htm
Types of igneous Rocks
Basalt
Basalt is a common igneous rock. The grains in basalt are fine
and small. It is usually dark with very small crystals. Large
pieces off basalt may split into many-sided columns.
Granite
Granite is made up of mainly coarse (large) grains of quartz,
feldspar, and mica. The individual grains in granite are large
because they formed as magma cooled slowly deep in the Earth.
It has the largest grains. Granite is usually speckled and varies in
color from gray to red according the different amounts of
minerals.
Obsidian
Obsidian is a glass formed from rapidly cooled lava. It forms so
quickly there is not time for crystals to grow. It has very sharp
edges. It looks like black glass.
Pumice
Pumice is hardened lava froth. Because the froth contains gas
bubbles, the rock is peppered with holes, like honeycomb. It is
very light and is usually gray. Pumice floats in water.
Scoria
Scoria has huge bubbles or holes in it. It is sometimes called lava
rock. It is usually dark in color, such as black, dark gray, brown,
or dark green. It is moderately heavy. It has few crystals.
Igneous Rocks Notes
What are they?
____________________________________________________________________________________
The two ways igneous rocks are formed:
1) __________________________
2)__________________________
When an igneous rock is cooled inside the Earth, the crystals
are ___________________ . They cool very slowly. These are called
intrusive igneous rocks.
When an igneous rock is cooled on the Earth’s surface, the
crystals are _________________. They cool very quickly. These are
called extrusive igneous rocks.
Magma that flows out onto Earth’s surface is called ___________________.
Igneous rocks are classified based on ___________________________ and
composition. Geologists look at the rocks surface and whether it
was formed by lava or magma.
Molten rock inside the Earth’s crust is called ______________________.
Exploring Igneous Rocks
List the 5 types of igneous rocks and describe each.
Rock Name
1)
2)
3)
4)
5)
Description- What do you notice? Look at its
crystal size, texture, color, etc.
Do you think the rock was cooled above
or below the Earth’s surface (intrusive
or extrusive)? Why?