Download Igneous Notes - Red Hook Central Schools

Rock Concept Map
Igneous
Rocks
ESRT
page 6
1. Igneous rocks form from the
cooling or SOLIDIFICATION
of magma (melted rock)
LIQUID HOT MAGMA
2. Magma is a mixture of
liquid rock, crystals, and gas
3. Magma is less dense than
surrounding rocks, and will
therefore move upward
B. Types of Igneous
Rocks
1.The cooling rate of
magma differs,
causing the crystal
size to also differ
a. intrusive igneous rocks
• Forms by the
slow cooling of
magma
underground
– “IN” –trusive
/ “IN” the
ground
– Also known as
PLUTONIC
• Because underground
cooling is SLOWER:
– Rock crystals are
LARGER & have a
coarse texture
gabbro
pegmatite
granite
Granite Mineral Composition
b. igneous rocks
• Fast cooling
of LAVA
(magma that
has reached
earth’s
surface)
Lava flows forming
extrusive igneous rocks
(obsidian)
• Because the lava Cools
QUICKLY (exposed to
colder air), rock
crystals are SMALL
and rocks have a
fine/glassy texture
Rate of Cooling Activity
• When I say “Go” try to find other
students in the class who have the
same color that you have- PLEASE
WALK!
• When I say “Stop”, stop exactly
where you are and do not move until I
say “GO” again
• What happened as I gave you a longer
amount of time to find each other?
Pumice is an Extrusive Igneous Rock that is
VESICULAR (has gas pockets). Because pumice
formed so quickly, the rock formed around the
pockets of gas, creating “holes” in the rock. This
allows the rock to float in water because of its
lower density
All light in color, low in density,
made up of the same minerals, and
felsic in composition…. What’s the
difference? COOLING TIME!
Key idea:
-The texture of the igneous
rock is determined by the
size, shape, and arrangement
of the mineral crystals NOT
if it is smooth or bumpy
-Rock texture is by
SIGHT/SIZE, not by TOUCH
types of magma
• FELSIC MAGMA
– Light colored
– Thick (high
viscosity)
– Contains high
amounts of silica
• Ex. Granite
• MAFIC MAGMA
– Dark colored
– Thin (low viscosity)
– Contains high
amount of
magnesium & iron
• Ex. Basalt
Mafic or Felsic?
the “bells & whistles” for
identifying an IGNEOUS rock
1. Obvious crystals in a
random order
2. Glassy texture
3. Air pockets