Igneous Textures

Question 1

Broad classification of igneous rocks based on the degree of crystallinity.

Answer 1

Igneous Textures

Question 2

Fully developed crystals with clear faces, formed from slowly cooling magma.

Answer 2

Euhedral/ Idiomorphic

Question 3

Partially complete crystal form

Answer 3

Subhedral

Question 4

Crystals that lack any observable faces; fitting into available spaces between other crystals.

Answer 4

Anhedral/ Xenomorphic

Question 5

A mix of euhedral, subhedral, and anhedral grains.

Answer 5

Hypidiomorphic-granular Texture

Question 6

Wholly glassy texture

Answer 6

Holohyaline

Question 7

Partially crystalline/ partially glass texture

Answer 7

Hypocrystalline

Question 8

Wholly crystalline texture

Answer 8

Holocrystalline

Question 9

contains small crystals less than 1 mm in diameter, and are associated with volcanic rocks that cool quickly on Earth’s Surface

Answer 9

Aphanitic

Question 10

Igneous rocks with crystals so small that even a microscope can’t see them clearly.

Answer 10

Cryptocrystalline

Question 11

Rocks with small crystals that are visible with a petrographic microscope.

Answer 11

Microcrystalline

Question 12

Very small crystals that can’t be seen with the naked eye but can be identified using a petrographic microscope.

Answer 12

Microlites

Question 13

large crystals averaging 1mm to 30mm

Answer 13

Phaneritic

Question 14

1 mm - 3 mm

Answer 14

Fine-grained

Question 15

3 mm - 10 mm

Answer 15

Medium-grained

Question 16

10 mm - 30 mm

Answer 16

Coarse-grained

Question 17

This texture has two different crystal sizes because the rock cooled in two stages.

Answer 17

Porphyritic

Question 18

Phenocrysts forms in what size of crystal?

Answer 18

LARGE

Question 19

What is fine-grained material in a porphyritic rock.

Answer 19

Groundmass

Question 20

Type of porphyritic texture where all crystals are visible to the naked eye, with phenocrysts being larger than the surrounding groundmass.

Answer 20

Porphyritic-Phaneritic

Question 21

Type of porphyritic texture where the phenocrysts are embedded in a groundmass that is too fine-grained to see clearly.

Answer 21

Porphyritic-Aphanitic

Question 22

Large crystals averaging more than 30 mm in diameter, and develop most commonly in granitic plutons with high volatile contents.

Answer 22

Pegmatitic

Question 23

What is an igneous rocks with pegmatitic texture?

Answer 23

Pegmatite

Question 24

This measures how many new crystals form in a certain amount of space over a certain amount of time.

Answer 24

Crystal Nucleation Rate

Question 25

rate at which your magma cools, which is the main factor for the formation of textures.

Answer 25

Cooling rate

Question 26

the availability ions that can fill specific ionic sites in a crystal lattice structure that can be enhance crystal growth

Answer 26

ion availability

Question 27

rate at which elements migrate through magma that depends primarily on the viscosity of the melt.

Answer 27

Diffusion

Question 28

An element that thicken magma, slowing crystal growth.

Answer 28

Network Formers

Question 29

an igneous rock texture primarily composed of glass that develop in lava that solidifies without experiencing significant crystallization

Answer 29

Glassy/ Holohyaline

Question 30

an amorphous solid possessing a disordered form

Answer 30

Glass

Question 31

This happens when molten rock comes into contact with air or water, causing it to cool very quickly.

Answer 31

Quenching

Question 32

An igneous rock texture that contains recognizable phenocrysts in a glassy groundmass

Answer 32

Vitrophyric

Question 33

A rock with a vitrophyric texture.

Answer 33

Vitrophyre

Question 34

A process where a glass turning into crystals

Answer 34

Devitrification

Question 35

are rounded masses of crystals that grow out from a central point during devitrification, often looking like small, radiating clusters.

Answer 35

Spherulite

Question 36

Black, glassy obsidian with cristobalite seeds that grew as “white snowflakes” within the obsidian.

Answer 36

Snowflake obsidian

Question 37

An igneous rock texture characterized by a cloudy appearance and rounded cracks

Answer 37

Perlitic

Question 38

A type of volcanic rock that is rich in silica (SiO₂) and has a glassy texture.

Answer 38

Perlite

Question 39

These are curved or spherical cracks that form in perlitic rocks as they cool, giving them a distinctive pattern.

Answer 39

Perlitic cracks

Question 40

A texture in igneous rocks that forms when gas bubbles get trapped in cooling lava.

Answer 40

Vesicular

Question 41

These are spherical or ellipsoidal void spaces

Answer 41

Vesicles

Question 42

A depth where volatiles exsolve from the liquid as a separate phase

Answer 42

Level of exsolution

Question 43

A process where small gas bubbles form in the magma above the level of exsolution.

Answer 43

Vesiculation

Question 44

This occurs when gas bubbles take up 70-80% of the magma's volume

Answer 44

Fragmentation surface

Question 45

A term used before a rock’s name if it contains 5-30% vesicles

Answer 45

Vesicular

Question 46

A term used for rocks with less than 5% vesicles.

Answer 46

Vesicle-bearing

Question 47

An igneous rock texture primarily made up of cemented or welded pyroclasts

Answer 47

Pyroclastic

Question 48

The rock particles of different sizes that are blown out during a volcanic eruption.

Answer 48

Pyroclasts

Question 49

Airborne pyroclastic material.

Answer 49

Tephra

Question 50

Rock fragment pyroclasts.

Answer 50

Lithic

Question 51

Glassy fragment pyroclasts.

Answer 51

Vitric

Question 52

Mineral or crystalline pyroclasts.

Answer 52

Crystals