Concept #2 Quiz

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Choose the best possible answer to the following questions about Key Concept 2 "Textures of igneous rocks and their interpretation."

This activity contains 7 questions.

The most important factor affecting the texture of an igneous rock is ________.

pressurechemical composition of the magma or lavaamount of space available for crystals to fillrate of cooling

Which of the following best describes an aphanitic texture?

The rock is crystalline, but mineral grains are too small to be seen with the unaided eye.The rock has mineral grains that are glassy.The rock contains broken fragments and is volcanic in origin.The rock is crystalline, but mineral grains are of distinctly different sizes.

Match the igneous rock texture and its appropriate description.

A matching question presents 4 answer choices and 4 items. The answer choices are lettered A through D. The items are numbered 3.1 through 3.4. Screen readers will read the answer choices first. Then each item will be presented along with a select menu for choosing an answer choice. Using the pull-down menus, match each item in the left column to the corresponding item in the right column.

	the rock has two or more distinctly different-size populations of mineral grains
	mineral grains are roughly equal size and coarse enough to be seen without the aid of a microscope or magnifying lens
	a non-crystalline rock, likely formed due to extreme rapid cooling of lava
	a magnifying glass or microscope is needed to see individual mineral grains

3.1 aphanitic	[hint]
3.2 porphyritic	[hint]
3.3 phaneritic	[hint]
3.4 glassy	[hint]

Volcanic glass and coarse-grained igneous rocks differ by which of the following?

The glass is formed mostly when lava cools in a volcano whereas phaneritic rocks cool at the surface.The glass is formed mostly when lava cools in contact with water whereas phaneritic rocks cool deep beneath the surface.The glass is formed mostly when magma cools deep beneath the surface whereas phaneritic rocks cool at the surface.The glass is formed mostly when magma is formed whereas the phaneritic rocks are formed in a volcano.

In a porphyritic texture, what is represented by the rock's “groundmass”?

the magma in the magma chamber before eruptionthe lava in the crystallizing magma chamber before eruptionthe lava after it erupted from a crystallizing magma chamberthe first crystals to form when the magma was in the magma chamber

Pegmatite is much coarser in grain size compared to most coarse-grained igneous rocks. What is a likely reason for this phaneritic texture?

The magma had an excessively long time to cool, allowing crystals to grow very large.The magma was rich in volatiles (like water) which aided in fast crystallization of large, but few numbers of crystals.Both of these.

Which of the following is the likely cause of a vesicular texture (open cavities in a rock)?

Each vesicle is filled by air and water.Each vesicle was filled by magma trapped in the solidified lava, and later escaped.Each vesicle was filled by a gas bubble when the lava was still mainly liquid.Each vesicle was filled by a crystal when the lava was mostly solid, and the crystals fell out later.

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