Lab 3 // Igneous Rocks

Question 1

Granite

Answer 1

Texture: phaneritic
Minerals/Groundmass: potassium feldspar, Na-rich plagioclase, quartz, biotite
Rock type: felsic
Processes:
-low temperature
-intrusive

Question 2

Granodiorite

Answer 2

Texture: phaneritic
Minerals/Groundmass: Na-rich plagioclase, quartz, biotite
Rock type: felsic
Processes:
-low temperature
-intrusive

Question 3

Basalt

Answer 3

Texture: aphanitic
Minerals/Groundmass: black groundmass
Rock type: mafic
Processes:
-high temperature
- extrusive / intrusive

Question 4

(porphyritic) Dacite

Answer 4

Texture: (porphyritic) aphanitic
Minerals/Groundmass: light grey groundmass with amphibole phenocrysts
Rock type: felsic
Processes:
-low temperature
-intrusive or intrusive
- two stages of cooling - slow first forming the phenocrysts and then fast to form the groundmass

Question 5

(porphyritic) Rhyolite

Answer 5

Texture: aphanitic / porphyritic
Minerals/Groundmass: light pink groundmass / red groundmass with quartz phenocrysts
Rock type: felsic
Processes:
-low temperature
-intrusive or intrusive
- two stages of cooling - slow first forming the porphyritic sample

Question 6

Diorite

Answer 6

Texture: phaneritic
Minerals/Groundmass: mainly amphibole and Na-rich plagioclase
Rock type: intermediate
Processes:
-intermediate temperature
-intrusive

Question 7

Peridotite (olivine)

Answer 7

Texture: phaneritic
Minerals/Groundmass: olivine
Rock type: ultramafic
Processes:
-very high temperature
-intrusive (earth's mantle)

Question 8

Scoria (vesicular basalt)

Answer 8

Texture: aphanitic and vesicular
Minerals/Groundmass: rusty red (oxidized) groundmass
Rock type: mafic
Processes:
-high temperature
-extrusive (with gas escaping to form the vesicles)

Question 9

Gabbro

Answer 9

Texture: phaneritic
Minerals/Groundmass: mostly Ca-rich plagioclase (striations), minor pyroxene (dull black)
Rock type: mafic
Processes:
-high temperature
-intrusive