1. CH. 3 – IGNEOUS ROCKS
Ignis =

2. Igneous Rocks
Cooling & crystallization of magma
Lava = molten
rock at surface

3. Igneous Rocks
Classified by:
Texture = crystal size of minerals
Composition = minerals present

4. Texture of Igneous Rocks
Depends on magma’s cooling rate
1) Cools slowly (stays liquid longer)
- crystals are (large, small)
2) Cools quickly
- crystals are (large, small)

5. Texture (Crystal Size)
Two environments where magma
cools:
1) Deep underground
2) At surface

6. Types of Texture
1) Fine-grained
- crystals invisible to naked eye
- magma cooled _________
- extrusive/volcanic

7. Types of Texture
2) Vesicular
- fine-grained w/ many holes in it

8. Types of Texture
3) Coarse-grained
- crystals easily visible
- magma cooled __________
- intrusive/plutonic

9. Types of Texture
4) Porphyritic
- two size crystals in same rock
Large crystals = ___________
Small crystals = ___________

10. Basalt porphyry

11. Porphyritic Texture
2-stage cooling process:
1st stage = slow cooling at depth
__________ is formed
2nd stage = rapid cooling of
remaining magma
____________ is formed

12. Types of Texture
5) Glassy
- no crystalline structure (magma
cools too fast)

13. Glassy Texture

14. Igneous Rock Classification
Composition = ______________
Mostly silica with varying amounts
of other six elements (Fig 2.21)

15. Crustal Composition

16. Igneous Compositions
Mafic
- 45-50% silica (“silica-poor”)
- rich in Magnesium, iron (Fe), &
calcium
- dark-colored: black, dark gray,
brownish-red

17. Igneous Compositions
Felsic
- 60-75% silica (“silica rich”)
- rich in aluminum, potassium, &
sodium
- light-colored: light gray, pinkish

18. Igneous Compositions
Intermediate
Fine-grained: medium gray
Coarse-grained: black & white
crystals

19. Importance of Igneous
Rocks
Compose 90% of Earth’s crust
Two types of crust:
Continental crust = ________
Oceanic crust = ________

20. Bowen’s Reaction Series
Sequence of minerals crystallizing
from magma (Fig. 3.13)
First minerals to form = _______
Last minerals to form = _______

21. Bowen’s Reaction Series

22. Bowen’s Reaction Series
As rock is heated:
First minerals to melt = ________
Last minerals to melt = ________

23. Important Concepts
A mineral is stable if the
environmental conditions are
similar to where it formed
Ex: temperature, pressure, water-
content

24. Stable
Ex:
Mafic minerals are stable under
____ temperatures
Felsic minerals are stable under
_____ temperatures

25. Important Concepts
If a mineral is put under different
environmental conditions, it
becomes unstable
- mineral reacts to new
environment by changing

26. New Environmental
Conditions:
If at the surface, weathering
occurs
If within the crust, metamorphism
occurs