CH 2 HW

Which two minerals are most common in detrital sedimentary rocks?

Clay minerals and quartz

Contact metamorphism takes place when rocks ____

Come in contact with magma body

What is the classification of igneous rocks based on?

Composition and texture

What is a coarse-grained rock composed of intermediate plagioclase feldspar and pyroxene?

Diorite

When lava erupts at Earth's surface, what type of rock is produced?

Extrusive

Working in the field, you see a very thin, dark-colored igneous sill across the valley. Without seeing the sill up close, what texture would you expect it to possess?

Fine-grained

Which structure is common in sedimentary rock?

Fossils, cross-bedding, mudcracks, ripple marks

What do we call a metamorphic rock that has a coarse-grained texture, minimal amounts of mica, and contains minerals that are segregated into bands?

Gneiss

What property of detrital sedimentary rocks can be indicative of the energy of sediment transport?

Grain size

What is the most efficient agent of metamorphism?

Heat

What agent might metamorphose rocks found adjacent to a large magma body?

Hydrothermal solutions

What element is principally responsible for making olivine, pyroxene, amphibole, and biotite dark?

Iron

Why does magma have a tendency to rise after its formation?

It is less dense than the surrounding rock.

What is the most abundant chemical sedimentary rock in Earth's crust?

Limestone

Why does quartzite not exhibit foliated texture?

There are very few or no tabular minerals in quartzite.

Which of the following agents is capable of moving sediment from the site of formation to the site of deposition?

Waves, running water, ice, wind

While working in the field, you discover an outcrop of metamorphic rocks. What can you conclude from this observation?

You know that these rocks formed at great depth below the surface

What process forms igneous rocks?

cooling and solidification of magma

An igneous rock that contains quartz and potassium feldspar would have a mineralogic content placing it in the range of _____.

granitic or felsic rocks

What do we call a metamorphic rock that has a coarse-grained texture, is dominated by mica, and contains no other notable minerals?

mica schist

Basalt is an igneous rock that can be identified by its small crystals. What are they composed of?

pyroxene and calcium-rich plagioclase feldspar

Basaltic igneous rocks contain which of the following minerals _____.

pyroxene and calcium-rich plagioclase feldspar

At a mid-ocean spreading center, alteration of rocks by chemically active fluids causes metamorphism by _____.

replacement or substitution of ions in the pre-existing rock

What is a fine-grained igneous rock composed primarily of very small crystals of potassium feldspar and a few large crystals of quartz?

rhyolite porphyry

As a result of partial melting, magma originates in _____.

the mantle and crust

The formation of sedimentary rocks requires _____

weathering and erosion of pre-existing rocks

Application of low-grade metamorphic forces to a rock causes _____

An increase in rock density

A geologist sends you a sample that was collected in the field. You find that it is a gray-colored igneous rock containing amphibole and intermediate plagioclase feldspar. Using Bowen's Reaction Series as a guide, how would you describe its composition?

Andesitic

Pyroclastic debris from a volcanic eruption can include _____.

Ash and cinders

Which one of the following igneous rocks contains no mineral crystals?

Obsidian

Metamorphic rocks can form when which of the following conditions are met?

Pre-existing rocks undergo metamorphism when they are subjected to heat and pressure without melting.

In addition to temperature, which of the following agents increases with depth in Earth?

Pressure

Which is an example of a sedimentary rock composed of solid masses of intergrown crystals?

Rock salt

In your field area you find a quartz sandstone unit with cross-bedding in it that is on the order of 2 m high. In what environment would you deduce this rock formed?

Sand dunes

The formation of sedimentary rocks occurs under what conditions?

Sedimentary rocks form when weathered particles are cemented and/or compacted.

Most igneous rocks are primarily composed of _____.

Silicate materials

What do we call a metamorphic rock that has microscopic to very fine-grained texture, breaks into slabs or sheets, and is dull on the surface?

Slate

In what type of igneous feature would you find rocks with a vesicular texture?

Surface of a lava flow

In addition to mineralogic composition, the degree of metamorphism in a rock is also characterized by _____.

Texture

Most igneous rocks never reach the surface. However, igneous rocks other than those formed in volcanoes are found exposed on many parts of Earth. How do you account for this phenomenon?

The formed at depth and have been exposed by uplift and erosion

When fine-grained tabular minerals in a rock at depth are subjected to differential stresses, they _____.

align perpendicularly to the plane in which the maximum compression stress is applied

For a detrital sedimentary rock that contains mudcracks, you could be confident that the environment in which it formed was _____.

alternately wet and dry

What is the term used to describe a very large, widespread, and deep intrusive body of igneous rock?

batholith

The geologic laboratory where you work received a sample for analysis that is composed of calcite that includes many microscopic fossils of marine organisms, reacts with acid, and is relatively soft. What name would identify this rock?

chalk

Working in the field, you find a rock that contains rounded fragments that are greater than 2 mm in diameter. What would you call this rock?

conglomerate