Igneous Rocks

Question 1

What are the three main magma types?

Answer 1

Mafic, Intermediate, and Felsic.

Question 2

What is the silica content and viscosity of mafic magma?

Answer 2

Low silica (~45–52%), low viscosity (flows easily).

Question 3

What type of volcanic eruptions does mafic magma produce?

Answer 3

Gentle eruptions (e.g., basaltic lava flows in Hawaii).

Question 4

What is the silica content of intermediate magma?

Answer 4

Moderate silica (~52–63%), medium viscosity.

Question 5

What kind of eruptions are common with intermediate magma?

Answer 5

Explosive eruptions at stratovolcanoes (e.g., Andesites).

Question 6

What is the silica content and viscosity of felsic magma?

Answer 6

High silica (>65%), very viscous (sticky, slow-flowing).

Question 7

What type of eruptions does felsic magma produce?

Answer 7

Very explosive, violent eruptions (e.g., rhyolitic magma at Yellowstone

Question 8

What is a batholith?

Answer 8

A massive intrusive body, >100 km² in area.

Question 9

What is a stock?

Answer 9

A smaller intrusive body (<100 km²).

Question 10

What is a sill?

Answer 10

A tabular intrusion that cuts parallel to rock layers.

Question 11

What is a dike?

Answer 11

A tabular intrusion that cuts across rock layers.

Question 12

What is a laccolith?

Answer 12

A mushroom-shaped intrusion that pushes overlying layers upward.

Question 13

What is a lava flow?

Answer 13

Surface flow of molten rock.

Question 14

What is a lava plateau?

Answer 14

Large, flat region created by repeated basaltic lava flows.

Question 15

What is a volcanic neck?

Answer 15

Solidified magma in a volcanic conduit, exposed after erosion.

Question 16

What is a pyroclastic deposit?

Answer 16

Rock fragments ejected during explosive volcanic eruptions.