Ch. 4 Magma, Igneous Rocks & Intrusive Activity

Well formed, floating crystals (phenocrysts) suspended in a finer grained, background matrix (groundmass) is an example of _________________ Texture?

Porphyritic

The texture composed of two distinctly different crystal sizes is?

Porphyritic Texture

The texture of an extrusive rock containing voids left by gas bubbles that escape as lava solidifies is?

Vesicular Texture (ex. Pumice)

Name 3 ways magma can be generated?

1. Decrease in pressure 2. Introduction of water 3. heat of crustal rocks

What are the four basic compositional groups of igneous rocks?

1. Granitic composition (Felsic) 2. Andesitic composition (Intermediate) 3. Basaltic composition (Mafic) 4. Ultramafic composition

What are the 3 major components of magma?

1. liquid portion called MELT 2. solid portion (if any) are crystals of silicate minerals. 3. gaseous portion called VOLATILES are materials that vaporize.

When magma crystallize at depth, ______A_____ igneous rocks form. When magma solidifies on Earth's surface, _____B_____ igneous rocks form.

A. Intrusive B. Extrusive

The texture composed of crystals that are too small for the individual minerals to be identified without a microscope?

Aphanitic Texture (fine-grained)

A large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and subsequently exposed by erosion is called?

Batholith = By definition, a surface exposure greater than 100 square kilometers, the largest intrusive igneous body

A concept proposed by N. L. Bowen that illustrates the relationships between magma and the minerals crysallizing from it during the formation of igneous rocks is called?

Bowen's Reaction Series

The formation and growth of a crystalline solid from a liquid or gas is called?

Crystallization

The gradual increase in temperature with depth in the crust is?

Geothermal gradient

The texture composed of unordered atoms and resembles dark manufactured glass is?

Glassy Texture (ex. Obsidian)

Higher Silica content = ___________ viscosity Low Silica content = ____________ viscosity

Higher Lower

A massive igneous body intruded between preexisting strata is called?

Laccolith

The texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter is?

Pegmatitic Texture

The texture composed of mineral grains that are large enough to be indentifed without a microscope is?

Phaneritic Texture (coarse-grained)

Large crystals in porphyritic rocks are referred to as _________?

Phenocrysts

When magma crystallizes at depth, it forms intrusive igneous rocks. What other name can these types of rocks be called?

Plutonic Rocks

Upon "blowing their tops", gas-rich, subduction-zone volcanoes generate 2 characteristic textures. Name them?

Pyroclastic & Porphyritic

The texture produced by the consolidation of fragments that may include ash, once molten blobs, or large angular blocks that were ejected during an explosive volcanic eruption is?

Pyroclastic Texture (fragmental)

Name 2 minerals that could be found in a MAFIC rock?

Pyroxene and Olivine

Name 2 minerals that could be found in a FELSIC rock?

Quartz, Potassium Feldspar

What reflects the overall mineral composition?

Rock color

Define Igneous Rock?

Rock formed from the crystallization of magma.

What is a pluton similar to but smaller than a batholith?

Stock

The term ______________ is used to describe the overall appearance of the rock based on the size, shape, and arrangement of its mineral grains - NOT how it feels to the touch.

Texture

Rocks that form when molten rock solidifies at the surface are classified as extrusive igneous rocks. What other name can these types of rocks be called?

Volcanic Rocks

Explosive volcanic eruptions produce bombs, blocks, lapilli and cinders = ejecta larger-than-ash, the rock that results from the settling and solidification of this material is called?

Volcanic breccia

An inclusion of unmelted country rock in an igneous pluton is called?

Xenolith