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PETROLOGY > Igneous Textures > Flashcards

Igneous Textures Flashcards

1
Q

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

A

Igneous Textures

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2
Q

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

A

Euhedral/ Idiomorphic

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3
Q

Partially complete crystal form

A

Subhedral

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4
Q

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

A

Anhedral/ Xenomorphic

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5
Q

A mix of euhedral, subhedral, and anhedral grains.

A

Hypidiomorphic-granular Texture

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6
Q

Wholly glassy texture

A

Holohyaline

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7
Q

Partially crystalline/ partially glass texture

A

Hypocrystalline

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8
Q

Wholly crystalline texture

A

Holocrystalline

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9
Q

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

A

Aphanitic

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10
Q

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

A

Cryptocrystalline

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11
Q

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

A

Microcrystalline

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12
Q

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

A

Microlites

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13
Q

large crystals averaging 1mm to 30mm

A

Phaneritic

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14
Q

1 mm - 3 mm

A

Fine-grained

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15
Q

3 mm - 10 mm

A

Medium-grained

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16
Q

10 mm - 30 mm

A

Coarse-grained

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17
Q

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

A

Porphyritic

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18
Q

Phenocrysts forms in what size of crystal?

A

LARGE

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19
Q

What is fine-grained material in a porphyritic rock.

A

Groundmass

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20
Q

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

A

Porphyritic-Phaneritic

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21
Q

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

A

Porphyritic-Aphanitic

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22
Q

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

A

Pegmatitic

23
Q

What is an igneous rocks with pegmatitic texture?

A

Pegmatite

24
Q

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

A

Crystal Nucleation Rate

25
Q

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

A

Cooling rate

26
Q

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

A

ion availability

27
Q

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

A

Diffusion

28
Q

An elements that thicken magma, slowing crystal growth.

A

Network Formers

29
Q

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

A

Glassy/ Holohyaline

30
Q

an amorphous solid possessing a disordered form

A

Glass

31
Q

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

A

Quenching

32
Q

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

A

Vitrophyric

33
Q

A rock with a vitrophyric texture.

A

Vitrophyre

34
Q

A process where a glass turning into crystals

A

Devitrification

35
Q

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

A

Spherulite

36
Q

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

A

Snowflake obsidian

37
Q

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

A

Perlitic

38
Q

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

A

Perlite

39
Q

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

A

Perlitic cracks

40
Q

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

A

Vesicular

41
Q

These are spherical or ellipsoidal void spaces

A

Vesicles

42
Q

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

A

Level of exsolution

43
Q

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

A

Vesiculation

44
Q

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

A

Fragmentation surface

45
Q

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

A

Vesicular

46
Q

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

A

Vesicle-bearing

47
Q

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

A

Pyroclastic

48
Q

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

A

Pyroclasts

49
Q

Airborne pyroclastic material.

A

Tephra

50
Q

Rock fragment pyroclasts.

A

Lithic

51
Q

Glassy fragment pyroclasts.

A

Vitric

52
Q

Mineral or crystalline pyroclasts.

A

Crystals

53
Q
A

PETROLOGY (9 decks)

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