Exam 4: Igneous Rocks and Intrusive Igneous Activity

A granite would form under conditions that included

Laccoliths are more similar to sills than they are to dikes.

A magma composed of more than 65% silica is referred to as

Geologists generally agree that batholiths are emplaced by forceful injection.

Magma that is forcefully ejected into the atmosphere as particles is known as

Pegmatite refers to

Natural glass such as obsidian forms when

Describe the role silica plays in controlling viscosity.

Volcanic necks form when

The magmas formed beneath spreading ridges are always felsic.

Ultramafic rocks are ___________found at the Earth's surface.

Batholiths typically contain

Volcanoes always erupt magmas of the same type.

Magma that cools below Earth's surface form most of the volcanoes in North America.

Rhyolite forms when a mafic magma cools on Earth's surface.

Magmas formed at subduction zones are mostly intermediate or felsic.

Partial melting explains the origin and composition of magmas at spreading ridges but not subduction zones.

If early-formed crystals settled out of a magma, the magma would tend to be

How do complex pegmatites differ from simple pegmatites?

Explain how we can tell, from a hand sample of an igneous rock, whether it formed as a volcanic rock or a plutonic rock?