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Igneous Rocks
Pages 129-134
Objectives
– Summarize three factors that affect whether rock melts.
– Describe how the cooling rate of magma and lava affects the texture of igneous
rocks.
• Relate cooling time to crystal size
– Classify ig rx according to their composition and texture.
– Describe intrusive and extrusive ig rx structures.
Origin of igneous rocks
• Igneous rocks are formed by _________________material from a volcano or
molten material within Earth
• Temps are 1600 at 60-200 km beneath the surface
Why is it so hot?
1. The deep rocks are under __________________from the rocks on top
2. Also … ________________________ ______________ produce heat
3. _____________________ ______________ from formation of the planet
Formation of magma
Three factors affect whether rock melts
1. ______________________________________________
2. ________________________________________________
3. __________________________________________________
Rocks have different _________________ points based upon the
________________________composition of their minerals
This means they crystallize (and melt) at different times
•
•
•
Partial Melting
Different minerals have different melting points, and minerals with
_____________melting points are the first to melt
This creates lava with a specific composition
As the magma heats up, ______________minerals melt and the magma’s
composition changes
Where do Igneous Rocks form?
Magma—_________________ Earth
Lava—___________________ Earth
Cooling time=__________________ ___________________
• Magma trapped underground is insulated so it cools _______________
• As it cools, the atoms arrange themselves in patterns to form _____________
• If the magma cools slowly, the atoms have time to arrange ________ crystals.
• These crystals are called
________________ _____________________
Rocks form when these mineral grains grow together.
Igneous Intrusive Rocks
• Rocks that form beneath Earth's surface are called _________________
________________________ rocks.
• They have crystals __________________ enough to see.
• We call this texture/grain size: _________________________
Granite
Granite is an ________________ _____________________ rock
It cooled ____________________ inside the earth
It has a ______________________________ texture
Diorite—salt and ____________________ look
Gabbro
•
A ________________, _________________, _____________________ rock
from the top of Bowen's Reaction Series.
Does gabbro have a high or low melting point? ________________________
Extrusive Igneous Rocks
• When rocks form from molten lava _____________________ Earth's surface
we call them _____________________ igneous rocks.
• They cool _____________________ so the atoms don't have time to arrange
themselves into patterns to form ____________________. They have a
__________________-___________________ texture.
• This texture is called ___________________________.
Rhyolite
Rhyolite is an _____________________ ______________________ rock
It cooled _________________, It has small grains
This is called an ___________________________ texture
It has the same mineral composition as _______________________.
Andesite Porphyry
• This is an andesite _______________________
• A porphyry has big _______________ in a _____________________
• Matrix—fine-_________________________________
Basalt
•
Basalt makes up the ____________________ ______________________
• It is a ________________, _________________, _________________ rock
Common Igneous rock terms
Vesicular
Hyaline
Pegmatite
Vesicular—______________________texture
Scoria formed when gassy lava cooled quickly above ground. You can see
where little pockets of air had been. Scoria is actually a kind of ___________ and
not a mixture of minerals.
Pumice
• Uses
– lava soap
– _______________-_________________ jeans
• Glass. Pumice has cooled too quickly for minerals to form. Very low density
• Chemical composition, however, will be from the bottom of Bowen's Reaction
series (i.e. felsic).
Hyaline texture—__________________ texture
• ___________________ --Volcanic glass
• Notice the _____________________ fracture
Pegmatite—_____________ ________________ mineral grains
Rock cools extremely _____________________, so very big mineral grains form.
Classification of Magmas
• Mafic—high in ______________and ______________________________
• Felsic—high in _________________ and ____________________(quartz)
• Mafic—_______% silica
– Colors-- black, green, red
• Intermediate—______% silica
• Felsic—______% silica
– Colors-- pink, white, light gray
Composition of Igneous Rocks
• _________________
—high in silica (quartz and feldspar)
Light colored
• _________________
—high in magnesium and iron
Dark colored
• ___________________
--A mixture of the two
In between colored
Melting point is also affected by two factors
•
•
•
•
The pressure
– As pressure
melting point
The water content
– High water content=_________________melting point
– Low water content=_______________________ melting point
Remember a rock is made of different minerals-- Bowen’s Reaction Series
When rocks melt, those with lowest melting points melt first
This is called ____________________ _________________________
When rock crystallize, those with highest melting points crystallize first as the
magma cools
– This is called ______________________ _________________________
Igneous Rock Structures
Igneous Rock formation beneath the Earth's surface
• Pluton-large intrusive igneous rock body
• Dike—cuts across rock layers-vertical
• Sill—horizontal –parallel to existing rock layers
Common Igneous Rock Pairs
Type of
Basaltic
Andesitic
Granitic
lava
(Mafic) (Intermediate) (Felsic)
Intrusive
diorite
granite
(phaneritic gabbro
texture)
Extrusive
basalt
andesite
rhyolite
(aphanitic
texture)