Igneous Rocks

Question 1

What is an Igneous Rock?

Answer 1

Formed:
Hot, molten rock (magma/lava) crystallizes and becomes solid.

Intrusive (formed within Earth)
Extrusive (formed on top of Earth’s crust)

Different compositions and textures determined by:
- where they solidified
- temperature
- melting conditions
-geological setting (plate tectonic setting)

Question 2

How is igneous rock formed? Partial melting.

Answer 2

Try to make this more clear:

• From the cooling and solidification of molten (melted) rock.
• Magma comes from subducting rock that undergoes partial melting.
• Rocks melt when pressure is reduced, temperature is high and water (subducting plate) is added

Question 3

What is Bowen’s Reaction Series?

Answer 3

The sequence in which minerals crystalize from a cooling magma

Question 4

What minerals crystallize first at high temperatures?

Answer 4

1. Olivine
2. Pyroxene
3. Amphibole
4. Biotite

Question 5

What are the last minerals to crystallize?

Answer 5

At lowest temperatures-

Feldspar
Mica
Quartz

Question 6

What minerals melt first?

Answer 6

The minerals that form at the lowest temperature

Question 7

What is fractional crystallization?

Answer 7

Process where crystallizing minerals change magma composition.

• During rocks melting elements are removed
• Other elements (Fe, Mg, Al, Ca, etc) crystallize so the process continues
• Minerals vary in composition due to crystallization process (mafic to more felsic)

Question 8

What is magma differentiation?

Answer 8

Chemical change in composition of the magma.

Processes of partial melting, fractional crystallization and others cause the magma to change composition forming different igneous rocks

Question 9

What is mafic rock vs felsic rock?

Question 10

What is intrusive rock vs extrusive rock?

Question 11

What are phenocrysts?