1. Chapter 3
Igneous
rocks

2. 2) contains a mixture of one or more minerals
Definition of a rock
-> different from that of a mineral. A rock:
1) is solid
2) contains a mixture of one or more minerals
3) occurs naturally as part of our planet

3. minerals rock mineral minerals collection of one or more A collection
So far we have:
minerals
rock
mineral
collection of
one or more
minerals
A collection
of one or more
types of atoms

4. Molten rock Some definitions inside the Earth is magma
when magma reaches Earth’s surface(outside) it
is called lava

5. Figure 4.1

6. An igneous rock is formed when magma or
lava cools and solidifies

7. Igneous rocks that form at the surface(lava)
Volcanic (extrusive) Igneous
Igneous rocks that form
at the surface(lava)
Plutonic (intrusive) Igneous
Igneous rocks that form
deep inside the earth (magma)

8. Plutonic rocks To see them, they must be uplifted to surface
And softer surrounding rock eroded away
Magma body

9. Plutonic rocks
For us to ever see them, they must be uplifted to the surface
And softer surrounding rock eroded away

10. Plutonic igneous rock example: El Capitan Yosemite Nat. Park,
California

11. As magma cools, atoms arrange in an
orderly crystal structure
crystallization

12. Note: different crystal sizes

13. Coarse-grained igneous rock
Close up of crystals
Note the variety of crystal sizes

14. Texture
a. size
b. shape
c. arrangement
the -
of interlocking crystals

15. cooling rate crystal size Slow cooling larger crystals Fast cooling
Coarse texture
Fast cooling
small or no crystals
Fine texture

16. Coarse-grained
Fine-grained
Large crystals in matrix
Glassy

17. fast cooling magma/lava forms at or near surface
sometimes holes present
can’t see individual crystals
forms far
below surface
slow cooling
intergrown
crystals
Aphanitic
Fine-grained
Phaneritic
Coarse-grained
very rapid
cooling
ions unable to
unite in orderly
crystalline
structure
magma cooled slowly for a
while then erupted.
minerals crystallize at
different temperatures and
or rates
Porphyritic
Glassy
Large crystals in matrix

18. Porphyritic
Texture

19. Aphanitic
Texture

21. Texture Rock types
Coarse grained Peridotite, Gabbro, Diorite, Granite
Fine grained Komatiite, basalt, andesite, rhyolite
Glassy Obsidian, Pumice, Scoria
Vesicular Pumice, Scoria
Prophyritic Andesitic porphyry
Phenocrysts –large very crystals.

22. mainly silicate minerals
determined by composition of magma from
which it crystallized
magma mainly 8 elements:
Si, O, Al, Ca, Na, K, Mg, Fe
Most abundant constituents

23. Figure 4.7

24. DARK silicates(simatic) LIGHT silicates(sialic)
Two major silicate mineral groups:
DARK silicates(simatic)
LIGHT silicates(sialic)
Silicate group
Rich in
Poor in
Examples
DARK
(Simatic)
Fe and/or Mg Si
olivine
pyroxene
amphibole
biotite
LIGHT
(Sialic)
Si, K, Na, Ca
Fe and/or Mg
quartz
muscovite
feldspars

25. Bowen’s Reaction Series
In a magma body:
crystals form as magma cools
heavy crystals sink to bottom
the composition of the magma changes
variety of igneous rocks from the same source

26. Bowen’s reaction series
Figure 4.23

27. Igneous rocks are classified from
A) texture
B) mineral composition
depends on: how fast/slow magma cools
depends on: chemical makeup of parent magma

28. mafic felsic high in Mg, Fe. Dark, dense
Igneous rocks types
mafic
felsic
magnesium + ferrum
high in Mg, Fe. Dark, dense
feldspar + silica (quartz)
high in Si. Lighter, less dense

29. zooming in
rhyolite
volcanic
f e l s i c
granite
plutonic

30. obsidian
volcanic
f e l s i c
volcanic
pumice

31. zooming in
andesite
volcanic
i n t e r m e d i a t e
diorite
plutonic

32. zooming in
basalt
volcanic
m a f i c
gabbro
plutonic

33. volcanic
m a f i c
scoria

34. magnesium + ferrum feldspar + silicate magma recipes
3 main types
magnesium + ferrum
high in Mg, Fe. Dark, dense
“mafic”
basaltic
andesitic
granitic
feldspar + silicate
high in Si, lighter, less dense
“felsic”

35. magma recipes basaltic andesitic granitic 3 main types “mafic”
magnesium + ferrum
high in Mg, Fe. Dark, dense
Most common volcanic
Igneous rock.
“mafic”
basaltic
andesitic
granitic
Most common plutonic
Igneous rock
“felsic”
“felsic”
feldspar + silicate
high in Si, lighter, less dense

36. magma recipes basaltic andesitic granitic 3 main types Partial
melt of:
“mafic”
basaltic
andesitic
granitic
mantle rock:
peridotite
Mantle peridotites
+ felsic crustal rocks
Si-rich continental
crust rocks
“felsic”
“felsic”

37. Kimberlite What is a kimberlite?
kimberlite is a potassic, ultramafic, igneous rock which occurs as small volcanic pipes.
Kimberlite commonly contains inclusions of upper mantle ultramafic rocks.
olivine, illmenite, pyrope, diopside,, enstatite and chromite.

38. Kimberlites are formed deep within the mantle, at between 150 and 450 kilometres depth, from exotic mantle compositions, and are erupted rapidly and violently.
It is this depth of melting and generation which makes kimberlites prone to hosting diamond.

39. Most kimberlites are confined to the ancient cratons
Most kimberlites are confined to the ancient cratons. The ages of most kimberlites are Late Mesozoic Era (Jurassic-Cretaceous).

41. Diamonds in the kimberlite

43. Kimberlite Indicator Minerals
Cr-pyrope (purple colour,), eclogitic garnet (orange-red), Cr-diopside (pale to emerald green), Mg-ilmenite (black, conchoidal fracture), chromite (reddish-black), and olivine (pale yellow-green) are the most commonly used kimberlite indicator minerals