Lab 2: Igneous Rocks

Question 1

Andesite. Colour, int/ext, and minerology

Answer 1

intermediate/extrusive;
aphanitic texture

plagioclase feldspar
amphibole

Question 2

where is andesite formed

Answer 2

Stratovolcano - rapidly cooled, felsic to intermediate shallow magma or lava

Question 3

Basalt colour, ext/int, texture, minerology

Answer 3

mafic/extrusive;
aphanitic texture

plagioclase feldspar
amphibole
pyroxene

Question 4

where is basalt formed

Answer 4

mid ocean ridge: rapidly cooled, mafic, pillow lava - mid

shield volcano: rapidly cooled, mafic lava

Question 5

Diorite colour, ext/int, texture, minerology

Answer 5

intermediate/intrusive;
phaneritic texture

plagioclase feldspar
amphibole

Question 6

where is diorite formed

Answer 6

stratovolcano felsic to intermediate magma chamber - slowly cooled

Question 7

Granite colour, ext/int, texture, minerology

Answer 7

felsic/intrusive
phaneritic texture

quartz
potassium feldspar
muscovite
biotite
plagioclase feldspar
amphibole

Question 8

where is granite formed

Answer 8

Stratovolcano: slowly cooled, felsic to intermediate magma chamber

Question 9

Gabbro colour, ext/int, texture, minerology

Answer 9

mafic/intrusive
phaneritic
(shiny/reflective + chunkier crystals)

plagioclase feldspar
amphibole
pyroxene

Question 10

where is gabbro formed

Answer 10

mid ocean ridge magma chamber; slowly cooled, mafic magma

Question 11

Obsidian

Answer 11

felsic/extrusive
glassy texture
conchoidal fracture

Question 12

where is obsidian formed

Answer 12

Stratovolcano: very rapidly cooled, low viscosity, felsic lava

Question 13

Peridotite

Answer 13

ultramafic/intrusive
phanertic
- can have green or be a greener black

olivine
pyroxene
plagioclase feldspar (small amount)

Question 14

where is peridotite formed

Answer 14

upper mantle, crystallized

Question 15

Pumice

Answer 15

felsic/extrusive
frothy

Question 16

where is pumice formed

Answer 16

stratovolcano: very rapidly cooled, gaseous felsic lava

Question 17

Rhyolite colour, ext/int, texture, minerology

Answer 17

felsic/intrusive
aphanitic

quartz
potassium feldspar
plagioclase feldspar
muscovite
biotite
amphibole

Question 18

where is rhyolite formed

Answer 18

Stratovolcano:
rapidly cooled, felsic to intermediate shallow magma or lava

Question 19

Scoria colour, int/ext, texture

Answer 19

mafic/extrusive
vesicular texture

Question 20

where is scoria formed

Answer 20

shield volcano:
very rapidly cooled gaseous mafic lava

Question 21

Volcanic Breccia

Answer 21

lithified ash and rock fragments

Question 22

percentage of silica in felsic

Answer 22

> 65

Question 23

percentage of silica in intermediate

Answer 23

55-65

Question 24

percentage of silica in mafic

Answer 24

45-55

Question 25

percentage of silica in ultramafic

Answer 25

<45

Question 26

major minerals in igneous rocks

Answer 26

quartz, k-feldspar, muscovite, biotite, plagioclase feldspar, amphibole, pyroxene, olivine

Question 27

vesicular texture

Answer 27

abundance of voids that once contained volatiles

Question 28

amygdaloidal texture

Answer 28

secondary infillings of vesicles by minerals

Question 29

frothy texture

Answer 29

more bubbles than rock

Question 30

pyroclastic

Answer 30

agglomeration of broken rocks, minerals, ash, and crystallized magmatic products - volcanic breccia

Question 31

aphanitic

Answer 31

crystals to small to identify in hand sample

Question 32

phanertic

Answer 32

visible crystals - think of camo

Question 33

phorphyritic

Answer 33

two stage cooling with larger crystals (phenocrysts) set in smaller crystals called the ground mass

all of the larger crystals are the same type of phenocryst

Question 34

in an igneous rock how can you recognize quartz

Answer 34

translucent, looks smoky grey

Question 35

in an igneous rock how can you recognize k-feldspar

Answer 35

pink

Question 36

in an igneous rock how can you recognize plagioclase feldspar

Answer 36

white in granite/diorite, grey in gabbro/peridotite
- twinning striations

Question 37

in an igneous rock how can you recognize biotite

Answer 37

black, can be flaked off with a knife

Question 38

in an igneous rock how can you recognize amphibole

Answer 38

black, slender crystals, duller lustre

Question 39

in an igneous rock how can you recognize pyroxene

Answer 39

black - not slender crystals, very vitreous