Igneous Rock

Question 1

Magma

Answer 1

Molten material formed underground.

Question 2

Lava

Answer 2

Surfaced magma.

Question 3

Extrusive (Volcanic)

Answer 3

Exiting the crust.

Question 4

Intrusive (Plutonic)

Answer 4

Entering the crust.

Question 5

Crystallization

Answer 5

Something crystallized, turning into solid form.

Question 6

Glass

Answer 6

No crystalline network due to very fast cooling.

Question 7

Vesicles

Answer 7

Air bubble holes (extrusive).

Question 8

Texture

Answer 8

The appearance of an igneous rock; NOT how it feels.

Coarse-Grain
Fine-Grain
Glassy

Question 9

Mafic Lava-Magma

Answer 9

Made of Magnesium (Mg) and Iron (Fe)

• Low-Silica content
• Basic type magma
• Hotter and more fluid
• Fast moving
• Dark color minerals and rocks form
• Mostly extrusive

Question 10

Felsic Lava-Magma

Answer 10

Made of Feldspar and Silica

• High-Silica content
• Acid type magma
• Thick and viscous
• Slow moving
• Light color minerals and rocks form
• Mostly intrusive

Question 11

Igneous rocks are classified by their __________ and _____________.

Answer 11

Texture and Composition

Question 12

Texture is based on the ______ and _____________ of the minerals (grains) within the rock.

Answer 12

Size and Arrangement

Question 13

The size and arrangement of minerals within the rock depends on the ______ ___ ________.

Answer 13

Rate of Cooling

Question 14

The rate of cooling depends on the _______ and ______ of the igneous body.

Answer 14

Depth and Size

Question 15

Phaneritic

Answer 15

Coarse grain, slow cooling, intrusive.

Question 16

Aphanitic

Answer 16

Fine grain, fast cooling, extrusive.

Question 17

Porphyritic

Answer 17

Shows fine and coarse grain, slow and fast cooling.

Question 18

What do porphyritic rocks contain?

Answer 18

Phenocrysts and Groundmass

Question 19

Phenocrysts

Answer 19

Early forming minerals.

Question 20

Groundmass

Answer 20

Fine grain material.

Question 21

Glassy

Answer 21

The result of very fast cooling.

Question 22

Pyroclastic

Answer 22

The consolidation of individual rock fragments that are ejected during a violent volcanic eruption.

Question 23

Families of Igneous Rocks

Answer 23

• Granite
• Diorite
• Gabbro
• Other

Question 24

Granite Family

Answer 24

High in Silica, made mainly of K Feldspar and Quartz, light in color.

• Granite (coarse-grain)
• Rhyolite (fine-grain)
• Obsidian (glassy)
• Pummus (frothy and vesicular)

Question 25

Diorite Family

Answer 25

Intermediate Silica content, intermediate in color.

• Diorite (coarse-grain)
• Andesite (fine-grain)

Question 26

Gabbro Family

Answer 26

Low in Silica, made mainly of Plagioclase and Augite, dark in color and more dense.

• Gabbro (coarse-grain)
• Diabase (medium-grain)
• Basalt (fine-grain)
• Scoria (vesicular)

Question 27

Other Igneous Rocks

Answer 27

• Dacite (between a Rhyolite and an Andesite)
• Peridotite (mixture of Olivine and Pyroxene, the Olivine gives it a greener tint differing it from Gabbro)
• Pegmatite
• Pyroclastic Rocks

Question 28

Pegmatite

Answer 28

A very coarse-grained igneous rock of any composition but most frequently granitic.

Question 29

Pyroclastic Rocks

Answer 29

• Tuff
• Welded Tuff
• Volcanic Breccia

Question 30

Tuff

Answer 30

The consolidated ash and pyroclastic fragments generated from a volcanic eruption.

Grain size

Question 31

Welded Tuff

Answer 31

Tuff formed by the welding together of hot volcanic glass shards at the base of pyroclastic flows.

Question 32

Volcanic Breccia

Answer 32

Composition is greater than ash-sized fragments. Angular fragments.

Grain size > 2mm

Question 33

Felsite

Answer 33

A general term for any light colored, aphanitic igneous rock, composed chiefly of Quartz and Feldspar.

Question 34

Igneous Rock

Answer 34

Rocks that come from molten material.