Chapter 4: Igneous Rocks (chart into word form)

Biotite

Name this mineral:

1) Liquid (melt)—the mobile ions mostly of the 8 common elements (silicon, oxygen, aluminum, iron, calcium, sodium, potassium, and magnesium). 2) Solid—consists of minerals that have crystallized from the magma as it cools. 3) Volatiles—consists of components that would form a gas at surface pressures, but are dissolved in the magma. The most common =water vapor -> carbon dioxide -> sulfur dioxide.

3 Components of Magma:

Batholith Largest intrusive body Occur as linear structures several hundred kilometers long Surface exposure of 100+ square kilometers (smaller bodies are termed stocks)

Define BATHOLITH

columnar jointing Occurs when igneous rocks cool and develop shrinkage fractures that produce elongated, pillar-like columns that often have six sides.

Define COLUMNAR JOINTS

Dike—a tabular, discordant pluton Magma was forcibly injected into fractures cutting across bedding planes Transport magma upward Parallel groups are called dike swarms Can also radiate from a volcanic neck like spokes on a wheel

Define DIKE

Aphanitic (FG): Composed of crystals that are too small for the individual minerals to be identified without a microscope. BASALT, RHYOLITE

Define Glassy texture give an example of a rock

Glassy texture: Composed of unordered atoms and resembles dark manufactures glass. OBSIDIAN

Define Glassy texture give an example of a rock

Phaneritic (CG): Composed of mineral grains that are large enough to be identified without a microscope. GABBRO, GRANITE

Define Phaneritic texture give an example of a rock

Porphyritic texture: Composed of two distinctly different crystal sizes. Pegmatitic rocks are found in intrusive rocks. Minerals grains are exceptionally large. GRANITE

Define Porphyritic texture as well as Pegmatite and give an example of a rock from both.

Pyroclastic (fragmental): Produced by the consolidation of garments that may include ash, once molten blobs, or large angular blocks that were ejected during an explosive volcanic eruption. TUFF

Define Pyroclastic texture give an example of a rock

Sill—a tabular, concordant pluton Nearly horizontal; magma exploits weaknesses along bedding planes Tend to accumulate magma and increase in thickness

Define SILL

Vesicular: Extrusive rock containing voids left by gas bubbles that escape as lava solidifies. SCORIA, PUMICE

Define Vesicular texture give an example of a rock

Granite is a felsic, coarse-grained igneous rock composed of light-colored silicates - quartz and potassium feldspar. Basalt is a fine-grained mafic igneous rock containing substantial amounts of dark colored silicates and plagioclase feldspar.

Difference between Granite and Basalt

Granitic or felsic composition: Light-colored silicates composed almost entirely of quartz and potassium feldspar Basaltic or mafic composition At least 45% dark silicates and calcium-rich feldspar, Contain no quartz! Higher density than granitic rocks

Difference between Granitic/Rhyolitic (Felsic) & Basaltic (Mafic)

Magma that crystallizes at depth forms plutonic or intrusive igneous rocks. The solidification of lava or volcanic debris forms volcanic or extrusive igneous rocks.

Difference between INTRUSIVE and EXTRUSIVE Magmas & Rocks?

Bowen's Reaction Series found by experiment proved that the order in which minerals crystallize from a basaltic magma depends on temperature. If the process continues, an original basaltic magma can change to first an andesite magma then a rhyolite magma with falling temperature

Explain the process of how Basaltic magma can become andesitic or rhyolitic in some continental environments

Most magma that erupts is basaltic (mafic) magma (Most originate from partial melting of mantle rocks at oceanic ridges. These melts are called primary or primitive magmas because they have not yet evolved.) Andesitic magma can form in two ways: -Magmatic differentiation of mantle-derived basaltic magma -Basaltic magmas assimilating crustal rocks Granitic magmas -Most form when basaltic magma ponds beneath the continental crust, heating and melting the much-lower melting temperature felsic minerals. -Can also form from magmatic differentiation of andesitic magma

How do Andesitic and Granitic magmas form?

Glassy texture: Composed of unordered atoms and resembles dark manufactures glass. Porphyritic texture: Composed of two distinctly different crystal sizes. Phaneritic (CG): Composed of mineral grains that are large enough to be identified without a microscope. Vesicular: Extrusive rock containing voids left by gas bubbles that escape as lava solidifies. Pyroclastic (fragmental): Produced by the consolidation of garments that may include ash, once molten blobs, or large angular blocks that were ejected during an explosive volcanic eruption. Aphanitic (FG): Composed of crystals that are too small for the individual minerals to be identified without a microscope.

Identify and describe the six major IGNEOUS TEXTURES

Basaltic (mafic) Granitic (felsic) Andesitic (intermediate) Ultramafic

List the 4 basic IGNEOUS compositions

Andesite Medium-gray, fine-grained rock Volcanic origin Commonly exhibits a porphyritic texture Diorite Intrusive equivalent of andesite Coarse-grained rock Looks like gray granite, but lacks visible quartz crystals

List the ANDESITIC (intermediate) Igneous Rocks:

Basalt Very dark green to black, fined-grained rock Composed mostly of pyroxene and calcium-rich plagioclase feldspar When porphyritic, contains small, light-colored feldspar or olivine phenocrysts Most common extrusive igneous rock Gabbro Intrusive equivalent of basalt Very dark green to black, phaneritic rock Composed mostly of pyroxene and calcium-rich plagioclase feldspar

List the BASALTIC (Magic) Igneous Rocks:

Granite Course-grained (phaneritic) One of the best known and most abundant igneous rocks 10−20% quartz, roughly 50% potassium feldspar Small amounts of (<10%) dark silicates Rhyolite Extrusive (fine-grained/aphanitic) equivalent of granite Composed essentially of light-colored silicates Typically buff to pink or light gray in color Obsidian Dark-colored, glassy rock Forms when silica-rich lava cools quickly at Earth's surface Usually black to reddish-brown in color Pumice Glassy textured rock with vesicular texture that forms when large amounts of gas escape from the lava Voids are quite noticeable and matrix resembles fine shards of intertwined glass

List the GRANITIC Igneous Rocks:

give the mineral grains time to grow larger mineral grains are smaller b/c they don't have as much time to grow

Magmas that cool at slow rate Magmas that cool faster

Tuff Most common pyroclastic rock Composed of ash-sized fragments cemented together Welded tuff Ash particles are hot enough to fuse together Can contain walnut-sized pieces of pumice and other rock fragments

Name 2 types of Pyroclastic Rock

Amphibole, Andesitic (intermediate)

Name this mineral:

BASALT: Basaltic (Mafic) Aphanitic (F.G.)

Name this mineral:

GABBRO: mafic - Basaltic intrusive equivalent to granite

Name this mineral:

GRANITE PORPHYRY *Granitic* -Porphyritic (2 distinct grain sizes)

Name this mineral:

Obsidian Felsic, Glassy texture.

Name this mineral:

Olivine *Ultramafic*

Name this mineral:

Peridotite *Ultramafic* Phaneritic (C.G.)

Name this mineral:

Pyroxene (Basaltic and Ultramafic)

Name this mineral:

Rhyolite, Aphanitic (fine grained) Granitic (Felsic)

Name this mineral:

Scoria, Vesicular texture that is Mafic -Basaltic

Name this mineral:

Tuff, Pyroclastic (fragmental) & Granitic (Felsic) Results from consolidation of volcanic ash

Name this mineral:

size, shape, and arrangement of a rock's constituent mineral grains. factors: mamga cool rate, silica content, amount of dissolved gasses (volatiles) in the magma

Texture is based on..

The type of rock The appearance of the rock as seen in its texture The type of rock body.

The environment in which magma completely solidifies to form a rock determines:

composed primarily of the ferromagnesian(iron & magnesium) minerals olivine and pyroxene with little or no calcium-rich plagioclase feldspar. ex: peridotite

ULTRAMAFIC

Phaneritic is coarse-grained are mineral grains large enough to see without a magnifying glass) The individual grains are too small to see, are called aphanitic. (Basalt)

What's the difference between Phaneritic (C.G.) and Aphanitic (F.G.)?

magma becomes more viscous and so moves more sluggishly & vice versa iron, magnesium & calcium content increases -silica content affects the viscosity of the magma

With more silica... As silica content decreases in the more mafic rocks: