Download Igneous Rock

Igneous Rock
Objectives
• Describe three ways that igneous rock
forms.
• Explain how the cooling rate of magma
affects the texture of igneous rock.
• Distinguish between igneous rock that
cools within Earth’s crust and igneous rock
that cools at Earth’s surface.
I. Origins Of Igneous Rock
A. Formation Igneous rock forms when
magma cools and hardens.
II. Composition and Texture of Igneous
Rock
A. Appearance Determined by Cooling
Rate Igneous rocks can be composed of
a wide variety of minerals. The texture of
igneous rock is determined by the rate at
which the rock cools.
http://geology.com/rocks/igneous-rocks.shtml
III. Igneous Rock Formations
A. Intrusive Igneous Rock When magma intrudes,
or pushes, into surrounding rock below the Earth’s
surface and cools, the rock that forms is called
intrusive igneous rock. Intrusive igneous rock usually
has a coarse-grained texture because it is well
insulated by surrounding rock and cools very slowly.
It also has large, visible crystals.
Diorite
III. Igneous Rock Formations
B. Extrusive Igneous Rock Igneous rock
that forms from magma that erupts, or
extrudes, onto the Earth’s surface is called
extrusive igneous rock. Extrusive rock is
common around volcanoes and does not
contain crystals.