1. Igneous Rocks Texture and Composition

2. 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

3. 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…
granite
well-formed

4. Crystallization of Salol Lab
Slow cooling made large, well-formed crystals
Quick cooling made small crystals
Slow cooling allowed for larger, well-defined crystals

5. Each mineral melts / crystallizes at its own temperature
Different minerals in granite crystalize at different temperatures. The last to cool has limited space to form crystals – so smaller not well-formed crystals
500°C

6. Group/Sort
Sort the igneous rocks into 3 groups by their crystal size: large small None: glassy or gas holes

7. Intrusive igneous Rocks

8. Intrusive igneous rocks slowly cool and crystalize inside the Earth forming plutonic rocks with large crystals

9. Violent pyroclastic
eruption
Ocean floor
LAVA
Fissure eruption

10. 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

11. Large, well-formed crystals AND small, fine crystals

12. Porphyritic Texture
Then it erupted out of a volcano to the surface and the rest of the magma cooled quickly forming small, fine crystals
The magma started to cool deep in the magma chamber and form large crystals

13. Igneous rock terms to have in your notes:
Magma - Lava
Intrusive – Extrusive
Plutonic – Volcanic
Course texture - Fine texture
Porphyritic - Pyroclastic
Mafic - Felsic
High viscosity – Low viscosity

15. Classification of Igneous rocks

16. Grouping by Composition
Sort the igneous rocks into 3 groups by their mineral colors: Dark: black, gray, green Light: clear, white, pink Intermediate: half dark/light

17. Silicates are divided by color
Ferromagnesium
Iron or magnesium
metal
Non-ferromagnesium Does NOT contain iron or magnesium

18. Felsic magma Ma”fe”c* magma
Page 121
Mafic
Felsic magma Ma”fe”c* magma
Feldspar, silica magnesium and iron

19. The silicon-oxygen tetrahedron (SiO4)- ion Combines with positive +ions (K, Na, Ca, Mg, Fe, Al) to form many different silicate minerals.
Show the GeoDe CD-ROM lesson on mineral groups

20. Igneous Rocks form from molten (melted) rock
Magma located
Lava located
Cooling rate is:
Crystals are:
Cooling rate:
Crystals are:
Porphyritic
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:

21. FELSIC (light) INTERMEDIATE MAFIC (dark)
FELSIC (light)
INTERMEDIATE
MAFIC (dark)
Color
Minerals
Name
Silica percent %
Thick or Thin
High or Low
VISCOSITY
Fast or Slow moving
Hotter or colder temp.?
Examples:
Names of the rocks

22. Mafic (dark) Dark colored minerals: Magnesium and iron Fe
Olivine, pyroxene,
Hornblende, augite, biotite
Less than 50% silica

23. Felsic (light) Light colored minerals: Quartz, orthoclase Feldspar
More than 60% silica

24. Which has a HIGH viscosity?
Resistance to flow
honey
water

25. Is this igneous rock intrusive or extrusive
Is this igneous rock intrusive or extrusive? Is it mafic or felsic in composition?
Name this rock: Rhyolite!
Felsic:
light-colored
High silica
content
fine crystals
extrusive,

26. Is this igneous rock intrusive or extrusive
Is this igneous rock intrusive or extrusive? Is it mafic or felsic in composition?
Name this rock – granite
course crystals,
intrusive
Felsic:
light-colored
High silica
and feldspar
content

27. Is this igneous rock intrusive or extrusive
Is this igneous rock intrusive or extrusive? Is it mafic or felsic in composition?
Name this rock – obsidian
NO crystals,
extrusive
Felsic:
(High silica
Content)

28. Is this igneous rock intrusive or extrusive?
BOTH!
It has
Course AND
Fine crystals,
So it’s
Intrusive AND
Extrusive????

29. ES0603 basalt diorite granite
rhyolite
basalt
Porphyritic
What??
basalt
Porphyritic
rhyolite
diorite

30. A B C
D E F

31. Edible Igneous Textures
Food/candy
name
Texture
Fine, coarse-grained, glassy, gassy,
porphyritic
Which igneous rock could this represent?

32. Match the food with the igneous rock texture
Next. Use to chart on page 124 to match and igneous rock to the food.
1.Course grained
2. Fine grained
3.Glassy
4.Gassy/porous
5.porphrytic

33. Edible Igneous Textures
Food/candy
name
Texture
Fine, coarse-grained, glassy, gassy,
porphyritic
Color:
Mafic, felsic.
intermediate
Which igneous rock could this represent?
Chocolate
Fine-grained
mafic
Basalt
Granola bar
Course-grained
Granite
Root beer barrel
glassy
looks mafic
(but it’s really just clear candy with brown food color, so it’s FELSIC)
obsidian
Marshmallow
gassy
felsic
pumice
Chocolate chip cookie
Porphyritic:
(fine-gained, with big crystals)
Felsic (background)
Porphyritic
(rhyolite)

34. Rock Poems I am fine-grained And so light stained.
My color ranges from light gray to pink, which probably makes you think…
rhyolite

35. 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

36. gabbro It may be coarse, it may be grainy.
It’s so dark, it makes you zany.
It contains pyroxene, 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

37. Smooth as glass - didn’t have much time. Got no crystals
I am so fine
Yes, I even shine.
Smooth as glass - didn’t have much time.
Got no crystals
Shot out of a volcano like a pistol
I’m felsic, but I don’t look it
Started to cool as soon as I reached the top
Here’s a hint, I’m an extrusive rock
obsidian