Chapter 5: Igneous Rocks

Question 1

What are the two main groups of igneous rock? (2)

Answer 1

Intrusive (cools from within Earth’s crust)

Extrusive (cools on surface)

Question 2

List and explain the four crystal sizes.

Answer 2

Phanetric: crystals can be seen by unaided eye, slow cooling
Aphantic: crystals cannot be seen, crystallizes in days
Glassy: cystallized in seconds and extrusive
Fragmental: Ejected from volcano as partly consolidated rocks

Question 3

Explain the three textures of phanetric rock (3)

Answer 3

Granular: Crystals are almost same in size and develops in all dimensions
Porphyritic: vibrates in one direction and small minerals
Poiklitic: molten matter became homogenous

Question 4

Describe dike and sill.

Answer 4

Dike: Comes to surface at high pressure and cuts through existing rock

Sill: Injected laterally and parallel with existing rock

Question 5

Name the two types of extrusive rock.

Answer 5

Lava flow (apahnitic) and pryoclastic flow (fragmental)