Igneous Rocks

Question 1

Granite

Answer 1

Coarse interlocking crystal matrix,
Euhedral
Potassium Feldspar, Quartz, Sodium, Amphibole, Mica
Formed Intrusively

Question 2

Rhyolite

Answer 2

Aphanitic
Feldspar, Quartz, no Amphibole (Maybe Biotite)
Formed Extrusively

Question 3

Diorite

Answer 3

Coarse Grained
Plagioclase, Amphibole, Pyroxene, Quartz
Formed Intrusively

Question 4

Gabbro

Answer 4

Coarse Grained
Calcium, Plagioclase, Pyroxiene, Olivine
Formed Intrusively

Question 5

Tuff

Answer 5

Aphanitic with Phenocrysts
Formed Extrusively from products of an explosive volcanic eruption
Often contains debris from bedrock and volcanic ash. Composition varies
Felsic

Question 6

Aphanitic

Answer 6

Small Crystals

Question 7

Phaneritic

Answer 7

Larger Crystals

Question 8

Pegmatitic

Answer 8

Very coarse crystals, larger than 3 centimeters

Question 9

Phenocrysts

Answer 9

Relatively large crystal embedded in an aphanitic matrix.

Question 10

Pegmatite

Answer 10

Form during the final stage of a magma’s crystallization.

Composed almost entirely of crystals at lease 1 cm in diameter

Question 11

Aplite

Answer 11

Forms during the final stage of a magma’s crystallization.
Intrusive rock
Aphanitic

Question 12

Felsic

Answer 12

Light in color

Question 13

Mafic

Answer 13

Dark in color

Question 14

Scoria

Answer 14

Vesicular Basaltic lava with small vesicles

Mafic

Question 15

Pumice

Answer 15

Vesicular volcanic rock containing volcanic glass and sometimes crystals
Felsic

Question 16

Vesicle

Answer 16

Cavity formed in volcanic rock by entrapment of a gas bubble during solidification

Question 17

Ignimbrite

Answer 17

Rock that shows direction of flow

Rock is formed from pyroclastic flow

Question 18

Porphyry

Answer 18

Rock that consists of large grained crystals (phenocrysts) embedded in a fine grained matrix

Question 19

Groundmass

Answer 19

The matrix of rock that is finer grained than the larger crystals that are embedded.

Question 20

Xenolith

Answer 20

A rock fragment which becomes enveloped in a larger rock during the latter’s development and hardening.
(Inclusions)

Question 21

Pyroclastic

Answer 21

Fragments of rock of explosive origin,

Volcanic Ash, Obsidian, and Pumice

Question 22

Lava Flow

Answer 22

Stream or sheet of molten or solidified lava

occurs on the surface

Question 23

Contact Metamorphism

Answer 23

Metamorphism due to contact with or proximity to an igneous intrusion

Question 24

Dike

Answer 24

Vertical Igneous Intrusion

Question 25

Sill

Answer 25

Horizontal Igneous Intrusion

Question 26

Lapilli

Answer 26

Volcanic rock materials which are formed when magma is ejected by a volcano.
2-64 mm in diameter
Means “Little Stones” in Latin

Question 27

Chill Zone

Answer 27

Border zone in intrusive igneous rocks that are fine grained because of rapid cooling.

Question 28

Reaction Rim

Answer 28

A border of secondary minerals formed at the margin of the primary grain in an igneous or metamorphic rock.

Question 29

Euhedral

Answer 29

Crystals that are well formed with sharp faces

Growth occurs in a free environment, unconstrained by adjacent minerals.

Question 30

Anhedral

Answer 30

Crystals that are not well formed

This crystal growth occurs in a competitive environment with no free space for the formation of crystal faces