Igneous Petrology (Part 2 - Intrusive Igneous Structures, Crystalline Forms) Flashcards
Plutons of more or less irregular shape with surface exposures _> 100km2
Batholith
Plutons with surface exposures _< 100km2
Stocks
A tabular, concordant pluton that parallels the country rock
Sill
A dome-like concordant pluton characterized by a dome roof and flat floor.
Laccolith
A dish-shaped concordant pluton that has a “champagne glass” appearance in a section view
Lopolith
Tabular intrusions that cuts through the country rock.
Dike
Cylindrical dikes exposed by erosion, and represents ancient conduits of old volcanoes.
Neck
Cylindrical pipes that can extend up to 20 km deep and develop through explosive intrusions.
Diatremes
Rocks that formed as a result of magma or lava cooling and solidifying
Igneous Rocks
Intrusive Igneous Rock
Plutonic
Extrusive Igneous Rock
Volcanic
A direct type of classification of composition that involves visual comparison of minerals and determining their volume percentages.
Modal Classification
An indirect type of classification of composition that analyzes the chemical composition of rocks
Normative Classification
Factors for Igneous Rocks Classification
Composition and Texture
Review table of Normative and Modal Classification
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A plutonic, very dark-colored (ultramafic) rock, depleted in SiO2.
Peridotite
A volcanic, very dark-colored (ultramafic) rock, depleted in SiO2.
Komatiite
Komatiite is characterized by?
Spinifex Texture
A plutonic, dark-colored (mafic), SiO2-poor (basic) rocks rich in plagioclase, pyroxene and olivine.
Gabbro
A volcanic, dark-colored (mafic), SiO2-poor (basic) rocks rich in plagioclase, pyroxene and olivine.
Basalt
A plutonic, salt and pepper-colored rock and generally contain more than half to almost two-thirds to SiO2.
Diorite
A volcanic, gray-colored (intermediate), rock rich in hornblende, pyroxene and plagioclase and generally contain more than half to almost two-thirds SiO2.
Andesite
A plutonic, light colored (felsic) rocks, containing approximately two-thirds SiO2. Can also be seen having a bit of pinkish hue
Granodiorite
A volcanic, light colored (felsic) rocks, containing approximately two-thirds SiO2.
Dacite
A plutonic, light colored (felsic) rocks, containing more than two-thirds SiO2.
Granite
A volcanic, light colored (felsic) rocks, containing more than two-thirds SiO2.
Rhyolite
Light colored, felsic, frothy, vesicular rock, less dense
Pumice
Dark-colored, felsic, frothy, vesicular rock, more dense
Scoria
A dark-colored silicic, non-crystalline igneous rock that has a glassy texture.
Obsidian
A dark-colored basic, non-crystalline igneous rock that has a glassy texture.
Tachylite
Complete crystal faces that are not impinged upon by other crystals, developed under circumstances such as slow cooling of magma.
Euhedral
Partially complete crystal form
Subhedral
Crystals that lack any observable faces
Anhedral/xenomorphic
A mix of euhedral, subhedral and anhedral grains
Hypidiomorphic-granular texture
Wholly crystalline texture
Holocrystalline
Partially crystalline/partially glassy texture
Hypocrystalline
Wholly glass texture
Holohyaline
Texture that contains small crystals less than 1 mm in diamater that are not generally discernible to the naked eye and are associated with volcanic rocks that cool quickly on Earth’s surface.
Aphanitic
What is the type of aphanitic that igneous texture with crystals too fine to be identified even with a petrographic microscope
Cryptocrystalline
Igneous texture containing minerals that can only be discerned using a petrographic microscope called microlites.
Microcrystalline
Crystals too small for the naked eye but large enough to be identified with a petrographic microscope.
Microlites
Characterized by crystals with diameters ranging from 1 to 30 mm but subdivided into three.
Phaneritic
a. fine grained - 1mm to 3mm
b. medium grained - 3mm to 10mm
c. coarse grained - 10mm to 30mm
Consists of two distinctly different crystal sizes due to a two stage cooling process
porphyritic
Large crystals in a porphyritic texture.
Phenocrysts
fine-grained material in a porphyritic texture
Groundmass
A type of porphyritic texture where all crystals are visible to the naked eye.
Porphyritic-phaneritic
A type of porphyritic texture where the phenocrysts are embedded in an aphanitic groundmass
Porphyritic-aphanitic
Characterized by large crystals averaging more than 30 mm in diameter
Pegmatitic
Igneous rocks with pegmatitic texture
Pegmatite
The number of new “seed” crystals that develop per volume per unit time.
Crystal Nucleation Rate
Factors affecting crystal nucleation
Cooling Rate
Ion Availability
Diffusion
The rate at which elements migrate through magma that depends primarily on the viscosity of the melt.
Diffusion
Elements that tend to increase molecular linkage which increases viscosity.
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, thereby lacking an ordered crystalline form.
Glass
Occurs when melts come into contact with air and water, rapidly absorbing heat, causing the melt to solidify rapidly before crystals could nucleate and grow.
Quenching
An igneous rock texture that contains recognizable phenocrysts in a glassy groundmass.
Vitrophyric
An igneous rock with vitrophyric texture.
Vitrophyre
A process when glasses crystallize into a solid state by growing on pre-existing microlitic or cryptocrystalline nuclei.
Devitrification
Rounded masses of radiating crystals that develop from devitrification.
Spherulites
black, glassy obsidian with cristobalite seeds that grew as “white snowflakes” within the obsidian.
Snowflake obsidian
igneous rock texture characterized by a cloudy appearance.
Perlitic
Glassy SiO2-rich volcanic rocks with a perlitic texture and higher water contents than obsidian.
Perlite
Curved or subpherical cooling cracks
Perlitic cracks
An igneous rock texture that are dominated by vesicles and develop due to exsolution and entrapment of gas bubbles in lava as it cools and solidifies.
Vesicular
Spherical or ellipsoidal void spaces.
Vesicles
A depth where volatiles exsolve from the liquid as a separate phase.
Level of exsolution
A process that occurs above the level of exsolution where volatiles nucleate as small bubbles
Vesiculation
Encountered when bubbles constitute 70-80% of the magma volume.
Fragmentation surface
A modifier of igneous rocks placed before the rocks’ names when they contain 5-30% vesicles.
Vesicular
A modifier for igneous rocks containing less than 5% vesicles.
Vesicle-bearing
An igneous rock texture primarily made up of cemented or welded pyroclasts.
Pyroclastic
Rock particles of varying sizes ejected by volcanic eruptions
Pyroclasts
Airborne pyroclasts ejected into the atmosphere
Tephra
Rock fragment pyroclasts
Lithic
Glassy fragment pyroclasts
Vitric
Mineral and crystalline pyroclasts
Crystals
