All About Igneous Rocks! (GEOL 101)

What can you mainly see in Granite?

Quartz, Feldspar, and Biotite

What are the 3 kinds of Rocks?

Igenous, Metamorphic, and Sedimentary

What kind of rock is the crust mostly made of?

Igenous and Metamorphic rocks

What is the most abundant rock on the surface?

Sedimentary rocks

How do Igenous Rocks form?

Solidification of magma or lava

What is the name of this rock?

Granite

What is the name of this rock?

Gabbro

What is the name of this rock?

Rhyolite porphyry

What is the name of this rock?

Basalt

What is Intrusive (Plutonic) Magma

Rocks formed beneath the surface by magma

What is Extrusive (Volcanic) lava?

Rocks formed at the surface by lava

What is Magma?

Molten rock below Earth’s surface.

What is Lava?

Molten rock on earth’s surface.

What is a Country Rock?

The rock that magma intrudes into

What are Igenous Rocks classified by?

Texture and Composition

What does Texture mean?

The size of mineral crystals

What does Composition mean?

What mineral it’s made of

Define Texture

As magma or lava cools, it solidifies, and minerals crystalizes

What are mineral crystals inside a rock sometimes called?

Mineral grains

What determines how large a mineral crystal grows?

Amount of time

What happens when magma cools slowly?

You can easily see mineral crystals

What happens when lava cools quickly?

Minerals are microscopic

What is a fine-grain texture?

An igneous rock made of microscopic mineral crystals

What is a coarse-grained texture

An igneous rock made of large mineral crystals

What is the 2 stage cooling process for some Igneous Rocks?

They start to cool slowly as a magma and then, they reach the surface, and grow microscopic mineral crystals

What is a Porphyritic Texture?

Rocks that have have both large and microscopic crystals.

What is a Porphyry?

A rock with a porphyritic texture

What is a glassy texture?

When lava cools too quickly the atoms do not have time to arrange themselves into a crystalline structure

What happens when lava cools too quickly?

The lava forms glass

What is Pillow Lava?

lava that erupted under water

What results from a pillow lava?

A rock with both a glassy (outside) and fine-grain (inside) texture

What kind of texture does this rock have?

Fine grain

What kind of texture does this rock have?

Coarse Grain

What kind of texture does this rock have?

Porphyritic

What kind of texture does this rock have?

Glassy

What are some common Igneous Rock Minerals

Quartz, Feldspar, Muscovite, Biotite, Amphibole, Pyroxene, and Olivine

Out of the common igneous rock minerals, which are felsic?

Quartz, Feldspar, Muscovite, Biotite, and Amphibole

Out of the common igneous rock minerals, which are mafic?

Pyroxene and Olivine

What does Felsic mean?

More silicon

What does Mafic mean?

Less silicon

What do Felsic Rocks have?

Higher Silicon Concentrations, Lower Melting Temperature, Higher Viscosity, and Light Colored

What does High Viscosity mean?

It does not flow easily

What color are Felsic rocks usually?

Light colored (pink and or gray)

What do Mafic Rocks have?

Lower Silicon Concentrations, Higher Melting Temperature, Lower Viscosity, and Dark Colored

What does Low Viscosity mean?

Flows easily

What color are Mafic rocks usally?

Dark colored (black)

What is helpful to determine if a rock is felsic or mafic?

Color

What kind of texture does Rhyolite have?

Fine grain

Is Rhyolite Mafic or Felsic?

Felsic

What kind of texture does Basalt have?

Fine grain

Is Basalt Mafic or Felsic?

Mafic

What texture does Granite have?

Coarse Grain

Is Granite Mafic or Felsic?

Felsic

What texture does Gabbro have?

Coarse grain

Is Gabbro mafic or felsic?

Mafic

What is an example of a ultramafic rock?

Peridotite

What is Peridotite mostly made up of?

Olivine

What is the mantle made up of?

Peridotite

What are Pyroclasts?

Lava that gets exploded from Volcanic eruptions that solidifies before it hits the ground

What is Volcanic Ash?

A type of pyroclast that has small fragments of glass formed by escaping volcanic gases

What is Pumice?

A type of pyroclast that has a frothy mass of glass with a large number of vesicles

How are pyroclasts deposited after an eruption?

In thick layers

How does Tuff form?

Pyroclasts that were hot enough to weld together

What is Tuff?

a hard igneous rock that is made up of welded pyroclasts

What 2 ways is magma usually formed?

Decompression Melting and Water-Induced melting

What is Decompression Melting?

Hot rocks rise near the surface, pressure is lowered, so the melting temperature decreases.

Where does Decompression Melting usually happen?

On Divergent Boundaries

What is Water-Induced Melting?

When water reduces the melting temperature of rocks. If “wet” rock enters the Earth and heats up, it will easily melt.

Where does Water-Induced Melting usually occur?

On Convergent Boundaries

As Pressure increases what happens to melting temperatures?

It gets higher

As Water Content increases what happens to melting temperatures?

It gets lower

What is Partial Melting?

The incomplete melting of a rock that occurs because the minerals that compose it melt at different temperatures

What happens if Peridotite is partially melted?

It forms Gabbro and Basalt

What is a Pluton?

Large igneous body of rock formed in the crust

What are the 2 kinds of Plutons?

Batholith and Stock

What is a Batholith?

A type of large Pluton

What is a Stock?

Anything smaller than a Batholith

What is a Sill?

A intrusion of Igneous rocks that are Parallel to the country rock

What is a Dike?

A intrusion of Igneous rocks that cut across the country rock

What was the most active and explosive Volcano in the US?

Mt. Saint Helens

How many months did Mt. Saint Helen gives clues to an eruption?

2 months

What is Mt. Saint Helens part of?

The Cascade Mountains

What are the Cascade Mountains?

A volcanic arc

What kind of convergent boundary are the Cascade Mountains on?

Ocean-Continent Convergence

What is another Volcano on the Cascade Mountains?

Mount Rainier

What are Volcanic Eruptions Preceded by?

Earthquakes, Swelling, and Increased Temperatures

What causes the early signs of eruptions in Volcanoes?

The rising of magma beneath the Volcano

Does Volcanism only happen on Volcanoes?

No

What is Volcanism?

The process by which magma rises through the crust and emerges at the surface as lava

What is a Volcano?

A hill or mountain constructed by an accumulation of lava and pyroclasts.

Where does MOST Volcanism usually occur?

On Divergent Boundaries

Where do Volcanoes usually form?

On Subduction Zones (Convergent Boundaries)

Where does SOME Volcanism Occur?

Interplate Volcanism (hotspots)

What is this?

A subduction zone

What is an example of hotspot volcanism?

The Hawaiian Islands

What is this?

Hotspot

What is a possibly explanation for Interplate Volcanism?

The Mantle Plume Theory

What is the Mantle Plume Theory?

Hot plumes of rock rise from the deep mantle (perhaps the core-mantle boundary) and reach the surface, forming hotspots

What is Basaltic Lava?

Hot, fast flowing, non-explosive lava

What are the kinds of Basaltic lava?

Flood basalts, Pahoehoe, Aa, and Pillow lavas