Igneous Textures Flashcards
Broad classification of igneous rocks based on the degree of crystallinity.
Igneous Textures
Fully developed crystals with clear faces, formed from slowly cooling magma.
Euhedral/ Idiomorphic
Partially complete crystal form
Subhedral
Crystals that lack any observable faces; fitting into available spaces between other crystals.
Anhedral/ Xenomorphic
A mix of euhedral, subhedral, and anhedral grains.
Hypidiomorphic-granular Texture
Wholly glassy texture
Holohyaline
Partially crystalline/ partially glass texture
Hypocrystalline
Wholly crystalline texture
Holocrystalline
contains small crystals less than 1 mm in diameter, and are associated with volcanic rocks that cool quickly on Earth’s Surface
Aphanitic
Igneous rocks with crystals so small that even a microscope can’t see them clearly.
Cryptocrystalline
Rocks with small crystals that are visible with a petrographic microscope.
Microcrystalline
Very small crystals that can’t be seen with the naked eye but can be identified using a petrographic microscope.
Microlites
large crystals averaging 1mm to 30mm
Phaneritic
1 mm - 3 mm
Fine-grained
3 mm - 10 mm
Medium-grained
10 mm - 30 mm
Coarse-grained
This texture has two different crystal sizes because the rock cooled in two stages.
Porphyritic
Phenocrysts forms in what size of crystal?
LARGE
What is fine-grained material in a porphyritic rock.
Groundmass
Type of porphyritic texture where all crystals are visible to the naked eye, with phenocrysts being larger than the surrounding groundmass.
Porphyritic-Phaneritic
Type of porphyritic texture where the phenocrysts are embedded in a groundmass that is too fine-grained to see clearly.
Porphyritic-Aphanitic
Large crystals averaging more than 30 mm in diameter, and develop most commonly in granitic plutons with high volatile contents.
Pegmatitic
What is an igneous rocks with pegmatitic texture?
Pegmatite
This measures how many new crystals form in a certain amount of space over a certain amount of time.
Crystal Nucleation Rate
rate at which your magma cools, which is the main factor for the formation of textures.
Cooling rate
the availability ions that can fill specific ionic sites in a crystal lattice structure that can be enhance crystal growth
ion availability
rate at which elements migrate through magma that depends primarily on the viscosity of the melt.
Diffusion
An element that thicken magma, slowing crystal growth.
Network Formers
an igneous rock texture primarily composed of glass that develop in lava that solidifies without experiencing significant crystallization
Glassy/ Holohyaline
an amorphous solid possessing a disordered form
Glass
This happens when molten rock comes into contact with air or water, causing it to cool very quickly.
Quenching
An igneous rock texture that contains recognizable phenocrysts in a glassy groundmass
Vitrophyric
A rock with a vitrophyric texture.
Vitrophyre
A process where a glass turning into crystals
Devitrification
are rounded masses of crystals that grow out from a central point during devitrification, often looking like small, radiating clusters.
Spherulite
Black, glassy obsidian with cristobalite seeds that grew as “white snowflakes” within the obsidian.
Snowflake obsidian
An igneous rock texture characterized by a cloudy appearance and rounded cracks
Perlitic
A type of volcanic rock that is rich in silica (SiO₂) and has a glassy texture.
Perlite
These are curved or spherical cracks that form in perlitic rocks as they cool, giving them a distinctive pattern.
Perlitic cracks
A texture in igneous rocks that forms when gas bubbles get trapped in cooling lava.
Vesicular
These are spherical or ellipsoidal void spaces
Vesicles
A depth where volatiles exsolve from the liquid as a separate phase
Level of exsolution
A process where small gas bubbles form in the magma above the level of exsolution.
Vesiculation
This occurs when gas bubbles take up 70-80% of the magma’s volume
Fragmentation surface
A term used before a rock’s name if it contains 5-30% vesicles
Vesicular
A term used for rocks with less than 5% vesicles.
Vesicle-bearing
An igneous rock texture primarily made up of cemented or welded pyroclasts
Pyroclastic
The rock particles of different sizes that are blown out during a volcanic eruption.
Pyroclasts
Airborne pyroclastic material.
Tephra
Rock fragment pyroclasts.
Lithic
Glassy fragment pyroclasts.
Vitric
Mineral or crystalline pyroclasts.
Crystals
