Igneous Rocks

Question 1

Glassy

Answer 1

Very rapid cooling usually from extruded lava in contact with cool air or cold water
(Hours - mins)

Question 2

Fine

Answer 2

Rapid cooling of extruded lava or the edges of intrusion that are in contact with cool surroundings
(Months - weeks )

Question 3

Medium

Answer 3

Minor intrusion about 1km deep (hypabassa) where cooling occurs over thousands of years

Question 4

Coarse

Answer 4

Major intrusion 10km+ (plutonic)

Question 5

Silica

Answer 5

SiO2

Question 6

<45% silica content

Answer 6

Ultramafic

Question 7

45-52% silica content

Answer 7

Mafic (dark colour)

Question 8

52-6% silica content

Answer 8

Intermediate

Question 9

> 66% silica content

Answer 9

Silicic

Question 10

Fine

Answer 10

<1mm

Question 11

Medium

Answer 11

1-5 mm

Question 12

Coarse

Answer 12

> 5mm

Question 13

Quartz

Answer 13

Magma is h over saturated in silica leaving some “leftover” once another mineral forms

Question 14

Hornblend

Answer 14

-intermediate
-black
-vitreous lustre
-2 cleavage 60 degree

Question 15

Augite

Answer 15

-black/ dark green
-vitreous lustre
-2 cleavage 90 degree

Question 16

Olivine

Answer 16

-vitreous lustre
-light green
-no cleavage

Question 17

Texture

Answer 17

-grain size
-shape
-relationship with crystals in an igneous rock

Question 18

Slow cooling

Answer 18

-euhedral
-prismatic
-sub-equant

Question 19

Rapid cooling

Answer 19

-sub-hedral
-anhedral

Question 20

Pegmatites

Answer 20

Huge crystals form as the result of magmas with large amounts of

Question 21

Glassy text

Answer 21

Very rapid cooling and so there are no discernible crystals
(Amorphous)

Question 22

Equigranular/ equicrystalline

Answer 22

Equal grain

Question 23

Vesicular

Answer 23

Many mangas contain dissolved gasses such as CO2 and water as pressure released the gases come out as a solution forming bubbles

Question 24

Amygdalaidal

Answer 24

Presence of vesicles in a rock can allow mineral rich waters percolate through and precipitates through in voids

Question 25

Porphyritic

Answer 25

Shows 2 distinct crystals sizes caused by 2 distinct cooling stages

Question 26

Phenocrystals

Answer 26

Large crystals that form fist and slowly

Question 27

Ground mass

Answer 27

Small crystals that surround the phenocrust These form later and rapidly

Question 28

Flowbanding

Answer 28

Common in rhyolite altering bands of lighter and darker minerals in parallel caused y flow of viscous magma

Question 29

Ophitic

Answer 29

Elongated crystals enclosed by another mineral Only seen in thin section

Question 30

Cumulate

Answer 30

Crystals settling in a magma will accumulate in contact with each over whilst continuing to grow Only seen in thin section

Question 31

Same cooling rate

Answer 31

Equagranolar

Question 32

2 stages og cooling 1- phenocrasto slower and deeper 2- ground mass deeper and closer to surface

Answer 32

Ponphanitic

Question 33

Gas evolve due to low pressure trapped

Answer 33

Vascular

Question 34

Water percolates through rocks and minerals precipitate in voids

Answer 34

Amugdalaldal

Question 35

Moves but is viscous

Answer 35

Flow banding

Question 36

1 crustal grow around others

Answer 36

Ophatic