Igneous Rocks

Question 1

IGNEOUS ROCKS formed by?

Answer 1

Solidification of magma

Question 2

slow cooling = ________ ?

rapid cooling = ________ ?

Answer 2

slow   =   CRYSTALLIZATION
rapid   =   QUENCHING

Question 3

Classified by? ( 2 )

Answer 3

1 ) COMPOSITION (chemistry)

2 ) TEXTURE (crystal size/shape)

Question 4

ULTRAMAFIC

• SiO2 content?
• Major Minerals?
• Rock Types (P/A) ?

Answer 4

• <45% SiO2
• Olivine, Pyroxene (pos amphibole, garnet)
• Peridotite (P)
• Komatite (A)

Question 5

MAFIC

• SiO2 content?
• Major Minerals?
• Rock Types (P/A) ?

Answer 5

• 45-52% SiO2
• Pyroxene, Olivine, Plagioclase (pos amphibole, biotite)
• Gabbro (P)
• Basalt (A)

Question 6

INTERMEDIATE

• SiO2 content?
• Major Minerals?
• Rock Types (P/A) ?

Answer 6

• 52-66% SiO2
• Plagioclase, Amphibole (pos biotite, potassium feldspar)
• Diorite (P)
• Andesite (A)

Question 7

FELSIC

• SiO2 content?
• Major Minerals?
• Rock Types (P/A) ?

Answer 7

• > 66% SiO2
• Potassium feldspar, Quartz (pos biotite, amphibole)
• Granite, Granodiorite (P)
• Rhyolite, Dacite (A)

Question 8

T A S Diagram

Answer 8

• Total Alkali vs. Silica content evolution
• used to group volcanic rock types
• composition dependent

Question 9

Dark minerals dominate?

Answer 9

Melanocratic

Question 10

Light minerals dominate?

Answer 10

Leucocratic

Question 11

2 Examples of MISLEADING Color

Answer 11

1) Obsidian >66% SiO2 but black

2) Dunite >90% Olivine but pale green

Question 12

Fine-grained (<1mm) ?

Answer 12

Aphanitic

Question 13

Coarse-grained (1-30mm) ?

Answer 13

Phaneritic

Question 14

VERY Coarse-grained (>30mm) ?

Answer 14

Pegmatitic

Question 15

Mix of large and small grains?

Answer 15

Porphyritic

Question 16

No crystals present?

Answer 16

Glassy (vitreous)

Question 17

Texture created by trapped gas bubbles

*More common in FELSIC (more viscous, trap gas more easily)

Answer 17

Vesicular

Question 18

Property of rocks that indicates ability of fluids/gases to flow through rock

Answer 18

PERMEABILITY

Question 19

Rocks that are formed in the Earth’s crust

Answer 19

Intrusive / Plutonic

Question 20

Rocks that are formed at the Earth’s surface

Answer 20

Extrusive / Volcanic

Question 21

No constraints of on space - clean crystal faces develop

Answer 21

EUHEDRAL

Question 22

Constraints on space - poor/no crystal faces develop

Answer 22

ANHEDRAL

Question 23

Mix of some crystal faces and no crystal faces

Answer 23

SUBHEDRAL

Question 24

Rocks that plot near P on QAPF (type + 3 EX)

Answer 24

MAFIC PLUTONIC ROCKS

• Anorthosite
• Gabbro
• Diorite

Question 25

Texture controlled by interplay of ? (2)

Answer 25

- Nucleation rates (how quickly new seed crystals are formed from melt) - Crystal growth rates (how quickly atoms build on a crystal lattice)

Question 26

Factors in texture controls ? (3)

Answer 26

- viscosity - ion availability - volatile composition (H2O, CO2, SO2 - volatiles prevent SiO2 bonding = keeps viscosity low)

Question 27

Si-deficient feldspar-like minerals ?

Answer 27

Quartz + Feldspathoids

Question 28

Temperature-depth relationship of the Earth

Answer 28

``` the GEOTHERM (melting points higher because of higher pressure) ```

Question 29

How are MELTS formed? (3)

Answer 29

- Temperature increase - Decompression - Volatile addition (H2O, CO2)

Question 30

________ : As temperature increases in a rock ______ minerals will break down first

Answer 30

PARTIAL MELTING; SILICA-RICH | SiO2, K2O, Na2O

Question 31

________ : As temperature decreases in a melt, ______ minerals crystallize first and fall out of solution

Answer 31

FRACTIONAL CRYSTALLIZATION; | MAFIC

Question 32

Edges of the magma chamber cool faster and crystallize first, leaving hot center

Answer 32

MARGINAL ACCRETION

Question 33

Crystal settling and floating

Answer 33

Gravitational Separation (differentiates magma chamber w/ layering)

Question 34

When crystals grow on wall of intrusion due to density currents

Answer 34

Convective Fractionation

Question 35

Melting of rocks around an intrusion, mixing with magma within the intrusion

Answer 35

Assimilation