Igneous rock Flashcards

Terms Definitions
phaneritic felsic
felsic-intermediate composition, glassy texture, usually black, glassy
fast cooling
fine grained
rocks with granitic composition
Extrusive, Felsic, Fine Grained
intrusive rocks
formed from magma
Porphyritic Andesite
intermediate composition, aphanitic texture, fine-grained, medium gray
Felsic minerals
the highest in silica
light-colored vesicular igneous rock. It forms through very rapid solidification
Crystalline Textures
o Pegmatiitic
o Aphanitic
o Phaneritic
o Porphyritic
igneous rocks formed above Earth's surface. Example: obsidian, also called volcanic rocks.
glassy igneous rock types
obsidian, pumice, scoria
a medium-gray, fine-grained rock of volcanic origin, it's name comes form South America's Andes Mtns.
decompression melting
when confining pressure drops enough
interesting fact of igneous rock
pumice floats
How thick is the upper mantle?
molten rock at or on surface
Intrusive igneous
(coarse grained)
- gabbro, diorite, granodiorite, granite
Phaneritic Gabbro
mafic, phaneritic, intrusive, looks like common rock
conspicously large crystal embedded in a matrix of finer-grained crystals
igneous rock:
formed by crystalization of Earth's magma (when it cools and hardens)
fine crystals, visible only with a microscope
having rounded cavities within a rock, formed during solidification by expansion of the gases present in the magma
Felsic or intermediate composition are?
Light colored rocks
mafic rocks
contain large proportions of pyroxenes and olivines
. Felsic
Mostly light colored minerals - potassium feldspar, sodium feldspar and quartz, with a small % of ferromagnesians.
What is a tuff?
A volcanic ash deposit
condition in which the earth's surface is worn away by the action of water and wind
Volcanic Rocks Naming
o Phenocryst phase
o Modifiers
o Chemographic rock type
- Example: olivine-plag phyric basalt
- QAPF of fine grained
A large depression typically caused by collapse or ejection of the summit area of a volcano.
no crystals, and very smooth
example is obsidian
glassy texture rocks
Igneous Rock
Are formed from the crystallization of magma (molten rock)
partial melting
the process by which most igneous rocks melt; because individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees; if the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results
form when fragments of lava are thrown high into the air
Ophiolite sequence
Sediment > pillow basalt > sheeted dikes > gabbro > peridotite = _______ _______.
aeolian sedimentary rocks
Deposits of sediment carried by air
Any rock composed of more than 90% olivine
- TAS diagram
o Total Alkalis vs. Silica
 Extremely fine grained or glassy rocks
 Plots total alkalis (NaO2 +K2O) against SiO2
Intermediate Color
More light colored than dark colored minerals
Vesicular texture
igneous rock that has large holes in it like swiss cheese, made when gases become trapped as bubbles.
glassy igneous rocks
more common in felsic; need fast freezing
Extrusive settings?
Cool at or near the surface
- cools rapidly
- chill too fast to grow big crystals
Extrusive Rocks
Rock that is formed from the magma cooling and crystallizing on Earth's surface
color, texture, mineralogy
what 3 characteristics are used to classify igneous rocks?
igneous rocks are the
most abundant rock on the earth
Ring of Fire
a major belt of volcanoes that rims the Pacific Ocean
Bowen's Reaction Series
This chart shows that minerals form in predictable patterns
What is a sill?
The contact between adjacent layers of rock.
What are some hazards associated with Rhyolitic volcanoes?
Very explosive eruptions, pyroclastic fall deposits
What are two current types of volcanism in NZ?
Intra plate volcanism (Auckland), and Subduction volcanism (Taupo volcanic zone, mt Taranaki)
What causes some rocks to have a glassy texture?
result of lava spew - randomly distributed ions
examples: obsidian, pumice
Mafic, Intrusive
Where is magma?
intermediate composition, phaneritic texture, small to medium sized crystals, salt and pepper appearance
Fine-grained (cannot be seen)
-an irregularly shaped, discordant pluton with at least 100 km2 of surface area (largest of all plutons)
-a large composite body produced by repeated voluminous intrusions of magma
-made of granitic igneous rocks or some diorite
conchoidal fracture
a curved, irregular break
Phaneritic of Granular, Quartz, Biotite, Orthoclase
largely created by mixing or differentiation, and compositionally lie between felsic and mafic magmas
igneous rocks that form at depth
Porphyritic Syenite
porphyritic phaneritic, felsic, has orthoclase,muscovite and biotite, and it does not scratch glass
Runs parallel to layers
ex) Palisades Sill, NYC
ex) Purcell Sill, Glacier National Park, Montana
o Pegmatiitic
 Large crystals >30mm
Large, euhedral early formation crystals, surrounded by later forming subhedral crystals.
igneous rock produced by eruption and solidified on or near the earth's surface
ex. rhyolite, andesite or basalt, obsidian
What is the mildest of all eruptions?
the liquid portions of magma excluding the solid crystals
fragment of rock distinct from the igneous rock in which it is enclosed
describe appearance of rock based on size, shape, and crystals.
Slow cooling deep beneath the earths surface allows crystal to grow to large size. brad jordan crys alot
Lava Very Basic, Form Outside The Volcano,Fined Grained Has Gas Pockets.
Porphyritic texture
large, well formed crystals surrounded by finer grained crystals of the same mineral
Extrusive igneous rocks
(fine grained)
- basalt, andesite, dacite, rhyolite
When magma reaches the surface, it cools quickly and solidifies into small mineral crystals in (volcanic, plutonic) igneous rock.
dark colored rocks high in iron and Mg
What is granite?
an intrusive, phaneritic igneous rock that has a low colour index (light colour) and is made of quartz and feldspar mineral crystal
crystal setting
the process whereby the minerals the crystallize at a high temperature in a cooling magma move downward in the magma chamber because they are denser than the magma
Fine-Grained Crystalline
Made of crystals too small to see.
What is magma?
Molten or partially molten silicate fluid, of variable temperature, composition, volatile content and crystal content
A body of magma or its solidified equivalent
a lump or mass of hard consolidated mineral matter
Identify the 4 types of magma
felsic magma
mafic magma
intermediate magma
ultramafic magma
pegmatitic texture
a texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter
Quartz, Plagioclase, Alkali Feldspar
Principal Minerals used in the classification of intrusive igneous rocks
M - mafic minerals
Olivine - fayelite, forresterite
Px - augite, diopside, pigeonite, aegerine, hyersthene, enstatite, bronzite
Amph - hornblende, riebeckite, richterite
iron and magnesium
what are the main minerals in high density rocks
Upward Movement of Magma
Once formed, magma tends to rise because it is less dense than solid rock. It does this by: Pushing, Melting, Quarrying, Moving through open fractures or vents (fastest).
Goals and principals of IUGS
- Create sustainable classification of ig rocks
o Use descriptive attributes
o Use actual properties
o Ensure suitability for al geologists
o Current terminology
o Define boundaries of rock species
o Simple to apply
o Follow natural relations
o Use modal mineralogy
o If not feasible, chemistry
o Follow terminology of other IUGS advisory bodies
silicic (felsic) rock or magma
silica-rich igneous rock or magma with a relatively high content of potassium and sodium
Al, K, Na, and Si
What are the major elements in the composition of felsic magma? (ABC order)
What are the properties of mafic magma?
hot and fluid (low viscosity), Large low profile shield volcanoes (Hawaii and Rangitoto island) , small steep explosive scoria cones (Stromboli and Auckland)
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