Chapter 10 Questions

Question 1

What are grains in a rock? How do they assist in classifying rock?

Answer 1

1. The size, shape and appearance of individual rock grains
2. Based on certain appearances grains can tell how a rock formed.

Question 1

What minerals make up granite?

Answer 1

Mica, feldspar, and quartz.

Question 2

Describe the three general types of course-grained igneous rocks.

Answer 2

1. Pegmatite: Exceptionally large crystal formation, rare minerals, almost entirely crystal.
2. Porphyry: Larger crystals embedded in a fine-grained groundmass.
3. Phanerite: small mineral grains that are more or less the same size.

Question 3

Compare the origin theories of the first igneous rocks. What were these rocks and where were they located?

Answer 3

• Old-earth: Magma hardened/cooled 4 bil. years ago and formed earth’s crust.
• Young-earth: God created first igneous rocks at the seperation of land and water, granite was original basement rock.

Question 4

Which type of magma formed most intrusive igneous formations? Which type formed most extrusive rocks? What can you oconclude about the source of extrusive magmas?

Answer 4

1. 90% of all intrusive igneous rocks are granitte and 90% of all extrusive igneous rocks are basalt.
2. The source of extrusive lavas is different from that of the rocks that make up the continental basement,.