Igneous Rocks

Question 1

The rate of cooling affects the texture

Answer 1

• Fast cooling: extrusive (at or near-surface)

- Slow cooling: intrusive (buried deeply), crystals are bigger b/c lots of time to grow

Question 2

Texture in igneous rocks describes:

Answer 2

• Crystal size
• Porosity (pores)
• If it is made up of fragments of volcanic debris

Question 3

Common igneous textures:

Answer 3

• Glassy (no crystals)
• Aphanitic (small crystals)
• Phaneritic (large crystals)
• Porphyritic (two crystal sizes = multistage cooling)
• Pyroclastic (fragments of rocks and crystals)
• Vesicular (holes/pores)

Question 4

What is the composition of igneous rocks?

Answer 4

The composition of an igneous rock is inherited from the molten rock from which it formed

Question 5

Felsic (lots of silica) mineral characteristics:

Answer 5

• Light in colour

- Iron and magnesium poor

Question 6

Mafic mineral characteristics:

Answer 6

• Dark in colour

- Iron and magnesium-rich

Question 7

The composition of the mantle is:

Answer 7

ultramafic

Question 8

If magma and lava come from the mantle, why aren’t all igneous rocks ultramafic?

Answer 8

• The mantle partially melts, lowest melting temps melt first which are chemically distinct from the rest of the mantle
• The most silica-rich minerals are preferentially extracted and turned into magma (lowest melting temps!!)

Question 9

Intermediate rocks contain more silica than mafic rocks. Can be produced through:

Answer 9

1. Crystal settling in a mafic magma (crystals pull out Fe and Mg, creating silica-rich magma)
2. Partial melting of a mafic rock
3. Mixing mafic magma with felsic magma
4. Assimilating felsic rocks into mafic magma

Question 10

Producing felsic magma requires many phases of:

Answer 10

partial melting and/or crystal settling to increase silica content

Question 11

Igneous Phaneritic Rocks

Answer 11

G.D.G

Granite, Diorite, Gabbro

Question 12

Igneous Aphanitic Rocks

Answer 12

B.A.R

Basalt, Andesite, Rhyolite

Question 13

Felsic Igneous Rocks

Answer 13

Rhyolite, Granite

Question 14

Intermediate Igneous Rocks

Answer 14

Andesite, Diorite

Question 15

Mafic Igneous Rocks

Answer 15

Basalt, Gabbro

Question 16

G.P.F

Answer 16

Granite = phaneritic, felsic

Question 17

R.A.F

Answer 17

Rhyolite = aphanitic, felsic

Question 18

D.P.I

Answer 18

Diorite = phaneritic, intermediate

Question 19

A.A.I

Answer 19

Andesite = aphanitic, intermediate

Question 20

G.P.M

Answer 20

Gabbro = phaneritic, mafic

Question 21

B.A.M

Answer 21

Basalt = aphanitic, mafic

Question 22

Add vesicular or

Answer 22

porphyritic in front of the base name of igneous rocks if present!