(MODULE 3) ROCK CYCLE & IGNEOUS ROCKS

Question 1

How are igneous rocks formed?

Answer 1

magma cools over time and solidifies. This process called crystallization occurs either beneath the surface or at the surface following a volcanic eruption. The resulting rocks are called igneous rocks.

Question 2

igneous rocks which form when magma erupts at the surface and rapidly cools.

Answer 2

Extrusive igneous rocks

Question 3

extrusive igneous rocks are also called ___.

Answer 3

volcanic rocks.

Question 4

igneous rocks which form when magma intrudes into bedrock and slowly cools.

Answer 4

intrusive igneous rocls

Question 5

intrusive igneous rocks are also called ___.

Answer 5

plutonic rocks

Question 6

igneous rocks are composed mainly of ___

Answer 6

silicate minerals

Question 7

Igneous rocks composed almost entirely of light-colored silicates like quartz and potassium feldspar belong to the ___ group and is described to have ___ composition.

Answer 7

granitic or felsic

Question 8

Rocks that contain at least 45 percent dark silicate minerals and calcium-rich plagioclase feldspar (but no quartz) are said to have a ___ composition.

Answer 8

basaltic

Question 9

Basaltic rocks contain a high percentage of ferromagnesian minerals, so geologists also refer to them as ___.

Answer 9

mafic

Question 10

This important category of igneous rocks is often associated with volcanic activity that is typically confined to the seaward margins of the continents and on volcanic island arcs such as the Aleutian chain.

Answer 10

andesitic

Question 11

rocks composed entirely of ferromagnesian minerals

Answer 11

ultramafic

Question 12

where is ultramafic rock often found?

Answer 12

upper mantle

Question 13

types of igneous texture:
1.
2.
3.
4.
5.
6.
7.

Answer 13

1. glassy
2. porphyritic
3. phaneritic (course-grained)
4. vesicular
5. pyroclastic (fragmental)
6. aphanitic (fine-grained)
7. pegmatitic

Question 14

When molten rock is ejected into the atmosphere during eruptions, rapid cooling will cause the ions to solidify before forming a crystalline structure, resulting in a ___.

Answer 14

glassy texture

Question 15

If molten rock containing large crystals undergoes a change in environment, the resulting rock which has large crystals embedded in a matrix of smaller crystals has a ___.

Answer 15

porphyritic texture

Question 16

The large crystals in porphyritic rocks are referred to as ___, whereas the matrix of smaller crystals is called ___. A rock with a porphyritic texture is termed a ___.

Answer 16

1. phenocrysts
2. groundmass
3. porphyry

Question 17

When large masses of magma slowly crystallize at great depth, they form igneous rocks that exhibit a coarse-grained texture described as ___.

The course-grained rocks are large enough to be identified without a microscope.

Answer 17

phaneritic

Question 18

Common features of many extrusive rocks are the voids left by gas bubbles that escape as lava solidifies. These nearly spherical openings are called ___, and the rocks that contain them are said to have a ___ texture.

Answer 18

1. vesicles
2. vesicular texture

Question 19

igneous rocks formed from the consolidation of individual rock fragments ejected during explosive volcanic eruptions have a ___ texture.

Answer 19

pyroclastic or fragmental

Question 20

Igneous rocks that form at the surface or as small intrusive masses within the upper crust where cooling is relatively rapid exhibit a fine-grained texture termed ___.

the fine-grained rocks has to be distinguished with a microscope

Answer 20

aphanitic

Question 21

best known igneous rock

Answer 21

granite

Question 22

dark-colored glassy rock

Answer 22

obsidian

Question 23

these rocks occur as small masses or thin veins within or around the margins of large intrusive igneous bodies, and form late in the crystallization of a magma.

such rocks have a ___ texture.

Answer 23

pegmatitic

Question 24

factors that influence the texture of igneous rock
1.
2.
3.

Answer 24

1. rate at which molten rock cools
2. amount of silica present in magma
3. amount of dissolved gases in magma

Question 25

a polymorph of diamond

Answer 25

graphite

Question 26

another term for silica rich rocks found in the continental crust

Answer 26

felsic

Question 27

silica-deficient rocks found in the oceanic crust

Answer 27

mafic