Chapter 4: Igneous Rocks

Peridotite

The partial melting of ____ will yield mafic (basaltic) magma.

Pyroxene

Which of these minerals would be the first to crystallize in a body of magma? (pyroxene, muscovite mica, quartz, sodium-rich plagioclase, potassium feldspar)

1. Magmatic differentiation 2. Assimilation 3. Magma mixing 4. Crystal settling

How can a magma body change its composition?

Basalt

A dike is mostly likely to be composed of which of the following igneous rocks?

Phaneritic

An igneous rock with a ______ texture solidified deep within Earth.

The introduction of water

At a subduction zone, melting is triggered by _____.

Gabbro: mafic Obsidian: felsic Granite: felsic Andesite: intermediate

Classify each of the following rocks by their mineral composition (felsic, intermediate, or mafic): gabbro, obsidian, granite, and andesite.

Intrusive igneous rocks form when magma cools and solidifies within Earth. Extrusive igneous rocks form when lava cools and hardens at the surface.

Compare and contrast extrusive and intrusive igneous rocks.

Diorite: intermediate with a phaneritic texture (crystals are so coarse that individual minerals can be distinguished with the naked eye) Rhyolite: felsic with an aphanitic texture (so fine-grained that their component mineral crystals are not detectable by the unaided eye) Basalt porphyry: mafic with a porphyritic texture (containing distinct crystals or crystalline particles embedded in a fine-grained groundmass)

Describe each of the following in terms of composition and texture: diorite, rhyolite, and basalt porphyry.

Crystals form by: 1. precipitating from a solution 2. freezing 3. deposition directly from a gas (rarely) Steps: 1. Nucleation: appearance of a crystalline phase from either a supercooled liquid or supersaturated solvent 2. Crystal growth: increase in the size of particles and leads to a crystal state

Describe the process of crystallization.

Granite and rhyolite are both felsic, but they differ in crystal size.

How are granite and rhyolite different? In what way are they similar?

Light-colored igneous rocks are more granitic (felsic) in composition and contain more feldspar and silica. Dark-colored igneous rocks are more basaltic (mafic) in composition and contain more iron and magnesium.

How do light-colored igneous rocks differ in composition from dark-colored igneous rocks?

Igneous rocks are made up of silicate minerals: potassium feldspar and quartz

Igneous rocks are composed mainly of which group of minerals?

Formed from particles that fused together, and composed of ejected fragments.

In what way does tuff and volcanic breccia differ from other igneous rocks such as granite and basalt?

1. Liquid: Melt 2. Solid: crystals of silicate minerals 3. Volatiles: dissolved gases in the melt that vaporize at surface pressure Most common volatiles in magma: 1. Water vapor (H2O) 2. Carbon dioxide (CO2) 3. Sulfur dioxide (SO2)

List and describe the three components of magma.

1. Granitic 2. Andesitic 3. Basaltic 4. Ultramafic

List the four basic compositional groups of igneous rocks, in order from the group with the highest silica content to the group with the lowest silica content.

Textures and compositions

List the two criteria by which igneous rocks are classified.

Plagioclase feldspar and quartz are minerals typically found in rocks with high silica content. Pyroxene and olivine are minerals typically found in rocks with low silica content.

Name two minerals typically found in rocks with high silica content and two minerals found in rocks with relatively low silica content.

Potassium feldspar and quartz

The most abundant minerals found in granitic (felsic) igneous rocks include ______.

Magma is composed of molten rock and is stored in the Earth's crust. Lava is magma that reaches the surface of our planet through a volcano vent.

What is magma? How does magma differ from lava?

Melt

Which component of magma includes mobile ions of silicon?

Phaneritic texture

Which of the following is a characteristic of an igneous rock found in a batholith?

Rhyolite

Which of the following is an aphanitic igneous rock?