Section 6.2 Igneous rocks
The Magma Process to form Minerals (Unit 4)
•Molten (liquid) rock in a magma chamber
At, near or under earth’s surface, RISES
•The magma begins to COOL. The atoms, ions and molecules combine to form various mineral compounds.
•The molecules arrange into an orderly repeating pattern to form CRYSTALS.
quartz
Igneous Rocks form from molten (melted) rock
Magma located
Lava located
Cooling rate is:
Crystals are:
Cooling rate:
Crystals are:
Intrusive igneous rocks
Where:
Extrusive igneous rocks
Where:
Very coarse grains
10 mm or larger
Coarse grains
1 mm -10 mm
Fine-grained
Less than 1 mm
Glassy or gassy
(no crystals grains)
Example rocks: Example rocks: Example rocks: Example rocks:
• The RATE at which the molten magma cools determines the crystal size.
• If the magma cools s-l-o-w-l-y
(under the surface taking hundreds of years)
then the crystals will be…
well-formed
granite
Crystallization of Salol Lab
Slow cooling made large, well-formed
crystals
Quick cooling made small crystals
Group/Sort
Sort the igneous rocks into 3 groups by their crystal size:
large
small
None: glassy or gas holes
Intrusive igneous Rocks
Igneous rock terms to knowIgneous rock terms to know
Magma - Lava
Intrusive – Extrusive
Plutonic – Volcanic
Mafic - Felsic
Course texture - Fine texture
High viscosity – Low viscosity
Porphrytic - Pyroclastic
Igneous Plutons (pg 125)
• Laccolith
• Volcanic neck
• Volcano
• Sill
• Dike
• Batholith
LAVA
Ocean floor
Fissure eruption
Violent pyroclasticeruption
• If the magma reaches the surface, erupts from a volcano as LAVA flows on the surface or erupts underwater, it cools quickly, and the crystals will be small / microscopic / not well-formed
basalt
• If the magma erupts explosively from a volcano and cools at a very fast rate, quickly, then the crystals will…. None
obsidian a volcanic rock, cools instantly. so it has no crystal structure, but a
glass-like structure
EXTRUSIVE
Felsic magma Mafec* magma
Page 121
Feldspar, silica magnesium and iron
Mafic (dark)
• Dark colored minerals:• Magnesium and iron Fe • Olivine, pyroxene,
Hornblende, augite,
biotite
• Less than 50% silica
Felsic (light)
• Light colored minerals:
• Quartz, orthoclase Feldspar
• More than 60% silica
Which has a HIGH viscosity?
honey
water
Resistance to flow
Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?
fine crystals
extrusive,
Felsic:
light-colored
High silica
content
Name this rock – page 124
Classification of Igneous rocksClassification of Igneous rocks
Large, well-formed crystals Large, well-formed crystals ANDAND
small, fine crystalssmall, fine crystals
Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?
course crystals,
intrusiveFelsic:
light-colored
High silica
and feldspar
content
Name this rock – page 124
Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?
NO crystals,
extrusive
Felsic:
(High silica
Content)
Name this rock – page 124
Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?
Course AND
Fine crystals,
Intrusive AND
extrusive
Course Mafic crystals
AND
Fine Felsic crystals
Name this rock – page 124
http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page05.cfm
Porphrytic Texture
The magma started to cool deep in the magma chamber and form large crystals
Then it erupted out of a volcano to the surface and the rest of the magma cooled quickly forming small, fine crystals
FELSIC INTERMEDIATE MAFICColor
Minerals (pr. 703)
Silica percent % % %
Thick or Thin
High or Low VISCOSITY
Fast or Slow moving
Hotter or colder temp.?
Examples: Names of the rocks
Section 6.2 pages 121-122 IGNEOUS ROCK: Textures
Porphyritic rocks begin to crystalize ___________________________, Then quickly harden at the __________________________________ Sketch a diagram of a rock with a porphyritic texture:
Ejected materials:
Extrusive rocks cool and crystalize at the _______________________ Their crystal size is __________________________________________ Examples of extrusive rocks:
Intrusive rocks cool and crystalize ______________________________ Their crystal size is __________________________________________ Examples of intrusive rocks:
After reading page 121-126in your notebook….
Select an igneous rock (2,3,5,6,7,9,11,14)
Rock _______#
Intrusive or Extrusive? ______________
Mafic or Felsic? ______________
Which Family? ______________
Bell workMatch the following terms to their definitions
1. Igneous rock that cools beneath the surface.
2. Igneous rock that contains both large and fine crystals.
3. A batholith and sill are examples.
4. Ash, cinders, and lava that erupt from a volcano.
5. An igneous rock that is both intrusive and extrusive.
Plutonic
Pyroclastics
Porphyrytic
Rock PoemsRock Poems
I am fine-grained
And so light stained.
My color ranges from light gray to pink, which probably makes you think…
rhyolite
This rock is rough and oh so tough.
This rock is not light, but dark as the night.
It’s mafic but not fantastic.
It’s found in the ocean and happens to be extrusive.
basalt
It may be coarse, it may be grainy.
It’s so dark, it makes you zany.
It contains feldspar, augite and olivine.
The sweet look of it is so divine.
What rock is this?
You don’t know?
Take a GUESS, it’s…. gabbro
I am so fineYes, I even shine.
Smooth as glass - didn’t have much time.Got no crystals
Shot out of a volcano like a pistolI’m felsic, but I don’t look it
Started to cool as soon as I reached the topHere’s a hint, I’m an extrusive rock
obsidian
A B C
D E F