Earth Science: Rocks and Minerals

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Questions and Answers

What are the characteristics of ultramafic igneous rocks?

They are composed primarily of orthoclase and quartz.

They contain a significant amount of dark silicate minerals. (correct)

They have low viscosity and form at temperatures above 1000°C.

They are mostly light-colored with high silica content.

Which igneous rock type is classified as intermediate based on silica content?

Basaltic

Granitic

Andesitic (correct)

Ultramafic

What is the typical viscosity of mafic magma compared to other types?

Same as honey

Similar to ketchup (correct)

Higher than treacle

Lower than that of peanut butter

Which of the following descriptions best fits granitic rocks?

They are coarse-grained and contain mostly quartz and feldspar. Signup and view all the answers

What distinguishes felsic igneous rocks from mafic igneous rocks?

Felsic rocks are generally light-colored and have >65% silica. Signup and view all the answers

Which type of sedimentary rock is primarily composed of sand?

Aranaceous Signup and view all the answers

Which type of igneous rock has an inferred cooling history based on its crystalline structure?

Granitic - coarse-grained Signup and view all the answers

Which rock type is characterized by having 45-55% silica content?

Mafic Signup and view all the answers

Which statement about the formation of igneous rocks is true?

Igneous rocks result from the melting, cooling, and crystallization of other rocks. Signup and view all the answers

What characterizes extrusive igneous rocks?

They cool quickly after magma reaches the Earth's surface. Signup and view all the answers

What type of texture is associated with igneous rocks formed from very rapid cooling?

Aphanitic texture with no visible crystals. Signup and view all the answers

Which igneous rock is classified as intrusive and related to slow cooling?

Granite Signup and view all the answers

What process leads to the formation of vesicular igneous rocks?

Rapid cooling that causes trapped gas bubbles. Signup and view all the answers

Which feature is key to understanding the cooling history of igneous rocks?

Crystal size and texture. Signup and view all the answers

What type of igneous rock typically forms above ground and is characterized by glassy texture?

Obsidian Signup and view all the answers

What defines a porphyritic texture in igneous rocks?

A mixture of both visible and nonvisible crystals. Signup and view all the answers

Study Notes

Definition of Rocks

Rocks consist of aggregates of minerals with varying melting points influenced by composition and water content.
Melting of rocks occurs in stages; processes include accumulation, precipitation, and changes from temperature, pressure, and fluids.

Igneous Rocks - Formation

Formed through the melting, cooling, and crystallization of existing rocks; originate from volcanic activity and mantle melting.
Magma cools and crystallizes into igneous rock either on the surface or beneath.

Types of Igneous Rocks

Extrusive (Volcanic) Rocks:
- Formed when magma erupts onto Earth's surface and cools rapidly.
- Characterized by small crystals; examples include basalt, rhyolite, and obsidian.
Intrusive (Plutonic) Rocks:
- Formed when magma cools slowly beneath the Earth's surface.
- Display large, well-formed crystals; examples include granite, gabbro, diorite, and dunite.

Texture of Igneous Rocks

Crystal Size: Indicates cooling history; larger crystals imply slower cooling.
Glassy Texture: Formed by very rapid cooling, lacking crystal structure; occurs on lava surfaces or in water.
Aphanitic Texture: No visible crystals; formed by fast cooling above ground.
Phaneritic Texture: Visible crystals; formed by slow cooling below ground.
Porphyritic Texture: Contains both visible and non-visible crystals from two cooling events.
Vesicular Texture: Features voids created by rapid cooling trapping air bubbles.

Color and Composition of Igneous Rocks

Dark Igneous Rocks:
- Composed of basaltic or mafic magma, rich in magnesium and iron; generally hot, around 1000°C.
Light Colored Igneous Rocks:
- Formed from silicic or felsic magmas, cooler (below 850°C) and more viscous (like peanut butter).

Classification by Composition

Igneous rocks classified by silica content and the presence of elements like K, Na, Fe, Mg, and Ca.
Categories:
- Felsic: Granitic, >65% silica, typically light-colored.
- Intermediate: Andesitic, 55-65% silica, medium gray in color.
- Mafic: Basaltic, 45-55% silica, usually dark-colored.
- Ultramafic: Contains mainly dark silicate minerals.

Specific Rock Types

Granite (Felsic): Coarse-grained, mostly orthoclase, albite feldspars, and quartz.
Basalt (Mafic): Contains dark silicate minerals and calcium-rich plagioclase feldspar.
Andesite (Intermediate): Features composition between granitic and basaltic.
Peridotites and Komatiites: Examples of ultramafic rocks.

Sediment Group: Arenaceous Rocks

Composed of sand, a loose granular substance formed from eroded rocks, prevalent in beaches, riverbeds, and deserts.

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Description

Explore the fascinating world of rocks and minerals in this Earth Science quiz. Discover the definitions, formation processes, and classifications of different rock types, including igneous and sedimentary rocks. Gain a deeper understanding of how rocks are formed and transformed in nature.