Igneous Rocks Lecture Flashcards

A set of 50 practice flashcards covering the definition, classification, and types of igneous rocks and intrusions based on the lecture notes.

What is an igneous rock?

A rock formed from the cooling and solidification of magma or lava.

What is the difference between magma and lava?

Magma is molten rock deep in the Earth’s crust, while lava is molten rock that erupts onto the surface.

In Hawaiian, what does the word 'Pahoehoe' mean?

Smooth lava.

What are the chemical and physical characteristics of Pahoehoe lava?

It consists of basalt or low silica and low viscosity.

What type of eruption is associated with Pahoehoe lava?

A volcanic eruption that produces a low rate of lava effusion and ropy masses of material.

What is the texture of Pahoehoe lava after it cools?

A ropy and smooth texture.

How is A’a lava described?

Rough, rubbly, and often sharp and jagged.

What rate of lava effusion is associated with A'a lava?

A higher rate of lava effusion.

What specific sound is associated with A’a lava during flow?

The sound of breaking glass.

What does A’a lava look like after it cools?

It leaves trails of largely black volcanic rocks.

What are pillow lavas?

Effusive volcanic eruptions that occur underwater.

How did pillow lavas get their name?

From the rounded shape of the lava chunks.

Where can pillow lavas be found in Oman?

In the Semail Ophiolite within the Hajar Mountains.

What is the appearance of blocky lava compared to A’a lava?

It forms several-foot-wide blocks that are rough but have a slightly smoother appearance.

What can blocky lava flows form if they pile up near an erupting vent?

A tall lava dome.

How far can thick lobes of blocky lava material reach?

More than a mile.

What material is contained in blocky lava flow after the eruption?

Obsidian.

How are intrusive igneous rocks formed?

From magma that cools and solidifies inside the Earth.

What is the typical timeframe for the formation of intrusive rocks?

A slow process that takes thousands to millions of years.

What is the general size of mineral crystals in intrusive rocks?

Large crystals.

According to the lecture notes, what is the crystal size of Granite?

Small crystals.

According to the lecture notes, what is the crystal size of Gabbro?

Medium (Med) crystals.

According to the lecture notes, what is the crystal size of Pegmatite?

Big crystals.

How are extrusive igneous rocks formed?

From lava that cools and solidifies rapidly on the surface of the Earth.

What is the typical timeframe for the formation of extrusive rocks?

A very fast process that takes seconds or minutes.

What is the crystal size of extrusive igneous rocks?

Very small, or they are not available at all.

What unique texture can form in extrusive rocks when air bubbles are trapped?

Vesicular texture.

List three examples of extrusive igneous rocks.

Rhyolite, Obsidian, and Pumice.

What is the typical texture description for intrusive rocks?

Coarse.

What is the typical texture description for extrusive rocks?

Fine.

At what crystal size is a rock considered 'coarse-grained' according to the transcript?

$1\,cm$.

At what crystal size is a rock considered 'fine-grained' according to the transcript?

$1\,mm$ (seen through a polarizing microscope).

On what basis are igneous rocks categorized as Felsic or Mafic?

The silica percentage in the rock.

Generally, how do Felsic and Mafic rocks differ in color?

Felsic rocks are lighter in color, while Mafic rocks are darker.

What feature indicates that an igneous rock cooled quickly?

Small mineral crystals.

What distinguishes a felsic extrusive rock (rhyolite) from a felsic intrusive igneous rock (granite)?

Crystal size.

Where is the most likely location for minerals to form quickly?

At Earth’s surface.

Which elements make up a large percentage of weight in most igneous rocks due to silica?

Silicon and oxygen.

What is the primary difference between felsic and mafic igneous rocks?

Mineral composition.

Felsic igneous rocks contain more __________ and are __________ in color compared to mafic rocks.

Silica; lighter.

What are plutons?

Large, irregular, coarser-grained igneous bodies formed deep underground by slow-cooling magma.

What is the difference between discordant and concordant intrusions?

Discordant intrusions cut across existing rock layers, while concordant intrusions run parallel to them.

What are batholiths?

Very large intrusive bodies that cover at least $100\,km^2$.

What is the difference between a batholith and a stock?

A stock is smaller than a batholith.

Define a 'dike' in terms of igneous intrusions.

A sheet-like body that cuts across existing rock layers (discordant).

Define a 'sill' in terms of igneous intrusions.

A horizontal sheet-like intrusion that runs parallel to rock layers (concordant).

What is a laccolith?

A dome-shaped intrusion that pushes the rock layer upward.

What are veins in the context of igneous intrusions?

Small mineral-filled fractures.

Which figure in the notes illustrates the difference between coarse and fine-grained rocks?

Figure 12.

Which specific rock is used as an example of a fine-grained rock in Figure 12?

Basalt.