JOURNAL #37
How
does a volcano work?
What are the parts of a volcano?
Refer to page 134 in your book
for help
TODAY WE WILL DESCRIBE 3
FACTORS THAT AFFECT WHETHER
ROCK MELTS AND CLASSIFY IGNEOUS
ROCKS ACCORDING TO THEIR
COMPOSITION AND TEXTURE
IGNEOUS ROCK
 When
magma cools and hardens, it
forms Igneous Rock.
 Because minerals crystallize as
igneous rock forms from magma,
most igneous rock can be identified
as crystalline.
 Magma form when rock melts.
IGNEOUS ROCK
 The
3 factors that affect whether
rock melts include:



Temperature
Pressure
Pressure of fluids in the rock
 Temperature

Rock melts when the temperature of the
rock increases to above the melting point
of minerals in the rock.
 Pressure

Rock melts when pressure is removed
from rock that is hotter than its melting
point.
 Pressure

of fluids in the rock
The addition of fluids generally decreases
the melting point of certain minerals in
the rock, which can cause those minerals
to melt.
PARTIAL MELTING
 Different
minerals have different
melting points, and minerals that
have lower melting points are the
first mineral to melt.
 The process by which different
minerals in rock melt at different
temperatures is called partial
melting.
FRACTIONAL CRYSTALLIZATION
 Opposite
of partial melting
 Chemicals in magma combine to
form minerals, and each mineral has
a different freezing point.
 As minerals freeze (crystallize) at
different times, those chemicals are
removed from the magma.
 The removal of different minerals as
magma cools is called fractional
crystallization.
TEXTURES OF IGNEOUS ROCKS
 Igneous
rocks are classified
according to where magma cools and
hardens


Intrusive Igneous Rock- rock
formed from the cooling and
solidification of magma beneath
Earth’s surface
Extrusive Igneous Rock- rock that
forms from the cooling and
solidification of lava at the Earth’s
surface
TEXTURES OF IGNEOUS ROCKS
 The
texture of igneous rock is determined by
the size of the crystals in the rock.
 The size of the crystals is determined by the
cooling rate of the magma.
 Examples:

Coarse-Grained Igneous Rock- large crystals


Fine-Grained Igneous Rock- small crystals


Granite
Basalt, Rhyolite
Porphyritic Igneous Rock- mixture of large and
small crystals

Obsidian, Pumic
COMPOSITION OF IGNEOUS ROCKS
The mineral composition of an igneous rock is determined
by the chemical composition
 Felsic Rock- describes magma or igneous rock that is rich
in felspars and silica and that is generally light in color.
 Examples: granite, pumice
 Mafic Rock- describes magma or igneous rock that is rich
in magnesium and iron and is generally darker in color.
 Examples: Basalt
 Intermediate Rock- lower proportions of silica than rock
sin the felsic familyand higher proportions of silica than
rock sin the mafic family
 Examples Diorite and Andesite

EXTRUSIVE IGNEOUS ROCK
STRUCTURES
 Igneous
rock masses that form on the
Earth’s surface are called Extrusions.
 A volcano is a vent through which magma,
gases or volcanic ash is expelled.
 When a volcanic eruption stops, the magma
in the vent may cool to form rock.
 The soft parts of the volcano are eroded by
wind and water.
 The solidified central vent is called a
volcanic neck.
YOU’RE ASSIGNMENT:
Work in PAIRS to complete Igneous Rock Review
 Use notes and pages 129-134 in your book
