Forms + HW's Review (Igneous Rocks)
Does felsic magma have a high or low viscosity?
high viscosity
Intrusive rocks can be...
course, very course
What percent of the rock has to be vesicles to be considered frothy?
50%
What percent of volcanic eruptions on Earth occur in the ocean?
90%
Glassy rocks can have a felsic or ________ composition
intermediate or mafic
Temperature plays a role in viscosity. If heat is added, what happens to a material's viscosity?
it becomes lower
What happens to silica content in igneous rocks as iron and magnesium content increases?
it decreases
What happens to the volume of the magma as it gets closer to Earth's surface?
it increases
Why does magma rise toward Earth's surface?
it is less dense than the rock surrounding it
What is the name of the extrusive, aphanitic ultramafic rock?
komatiite
What are phenocrysts?
larger crystals that formed at depth in the Earth
How does the gas content in magma affect explosivity of the eruption?
more gas = more explosive
What two minerals are missing from the chart that should be there?
muscovite + komatiite
As melted rocks cools what forms?
new textures + new minerals
If continental crust and oceanic crust collide, which crust is pushed (subducted) down beneath the other?
ocean (more dense)
Which crust is more dense?
oceanic
Where do most volcanoes exist...
on the plate boundries
What is another word for intrusive?
plutonic
Which term describes an igneous rock that is both intrusive and extrusive?
porphyritic
When we name porphyritic rocks, what is the third word used in it's name?
porphyry
The extreme __________ prevents the melting of material in the earth's interior.
pressure
Gases come out of solution when..
pressure is decreased
The most common volatiles in Earth's magmas are:
-carbon dioxide -water vapor -sulfide dioxide
The type of igneous rock that form depend on what factors:
-composition of the magma -amount of Ca/ Na in magma -rate at which magma cools
Intrusive rocks are rocks that form:
-deep underground
When magma cools, which mineral groups form:
-oxides -silicates -sulfates -sulfides -native elements
Extrusive rocks are rocks that form:
-underground but close to the surface -in the air -in ocean water
All igneous rocks can be grouped in to _____ types?
2 (extrusive, intrusive)
What is an effusive eruption?
An effusive eruption is a type of volcanic eruption in which lava steadily flows out of a volcano onto the ground.
It is harder for gases to escape from..
Felsic thick/sticky magma
What happens to the amount of water in a melt and composition.
Magma with high silica has high water content
The bottom of the crust is called the ______
Moho discontinutity
_________ volcanoes are effusive and just allow lava to pour out of the ground without an explosive violent eruption.
Shield
What type of volcano caused the worlds largest mass extinction?
Stratovolcanoes
_____________ are generally explosive.
Stratovolcanoes
What is a porphyry?
a fine grained rock with coarse grained phenocrysts
Low viscosity magma___.
allows gases to escape easily and quickly
Which word means very small crystals?
aphanitic (extrusive)
Cooled lava produces..
aphanitic rocks
As liquid magma rises, gases come out of the liquid solution because___.
as magma rises, there is less pressure so the gases start to escape
What are the two igneous rock properties we use to classify (name) igneous rocks?
composition + texture (grain size)
What type of tetrahedral structures do felsic rocks have?
complex structures
Felsic/intermediate lava forms what kind of volcano?
composite volcano
What 2 properties are used to name igneous rocks?
composition + texture
During subduction the lithosphere brings with it _______________.
contaminants
Which crust is less dense?
continental
Which factor determines the crystal size of igneous rocks?
cooling rate
As the magma rises, the pressure decreases causing ____________ melting, resulting in a more liquid composition.
decompression
As the silica tetrahedral structure becomes more complex, the ability of gases to escape from the lava...
decreases
Continental crust is more __________ in composition
felsic
Lava dome volcanos form from which type of lava?
felsic
Which type of lava forms steeply sided mountains...
felsic or intermediate lava
Which types of lava cause the most dangerous/explosive eruptions?
felsic or intermediate lava
Obsidian is...
felsic, intermediate
How are porphyritic rocks named?
first with their dominant phenocrysts then the aphanitic rock name then ending with "porphyry"
The holes in vesicular rocks form when...
gases come out of the magma
Extrusive rocks can be...
glassy, fine
What is the relationship between silica content and viscosity of magma or lava?
high silica causes high viscosity
The plate that is being pushed down into the earth experiences an ___________ in temperature and pressure.
increase
In general, how is the density of alight colored igneous rock different than the density of a dark colored igneous rock?
light colored rocks are less dense than darker colored rocks
The collection of tectonics plates comprises what we call the __________
lithosphere
Volatiles vaporize at..
low pressures
Oceanic crust is mostly ________ in composition
mafic
Gases more easily escape from..
mafic magma
The asthenosphere is part of which Earth layer?
mantle
Adding salt to water lowers the _______
melting pint
Is oxygen or silicon most abundant in Earth's crust?
oxygen
An ultramafic phaneritic rock is...
peridotite
Intrusive rocks have ____ texture
phaneritic
What colors can Potassium Feldspar be...
pink or white
Volcanic ash (Tuff) has which texture?
pyroclastic
What are rocks composed of rock fragments produced and ejected by explosive volcanic eruptions?
pyroclastic rocks
Extrusive rocks cooled..
quickly, above ground
What is viscosity?
resistance to flow
Mafic lava forms what kind of volcano?
shield volcano
Intrusive rocks cooled..
slowly, underground
How do Igneous rocks form?
solidification + cooling
What is another term for a composite volcano?
stratovolcano
How can you determine if an igneous rock had an intrusive or extrusive origin?
texture
When we name porphyritic rocks, what is the second word used in it's name?
the fine grained matrix
When we name porphyritic rocks, what is the first word used in it's name?
the name of the coarse grained mineral
How does the cooling rate of molten rock material affect the size of mineral crystals that form?
the slower the cooling rate, the larger the mineral crystals
As magma becomes more silica rich, it becomes..
thicker and more explosive
Mafic magma is..
thin and runny
All melts begin as what composition?
ultramafic
What is the term used to describe an igneous rock that has gas pockets throughout it?
vesicular
What is a pyroclastic rock composed of?
volcanic ash, crystals and rock fragments
Which contaminants cause the lithosphere to melt into a semi-liquid phase?
water and carbon dioxide gases which causes it to rise
Is it possible that magma never reaches Earth's surface?
yes