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