Igneous rock, also called magmatic rock, forms when molten material cools and solidifies. The molten material is called magma while it is beneath Earth’s surface. Once it reaches the surface, it is called lava. Cooling magma or lava can crystallize into a rock made of mineral grains, or it can solidify without crystallizing to form natural glass.
The location where molten material solidifies influences the type and texture of the resulting rock. Solidification below the surface produces intrusive rock; solidification at the surface produces extrusive rock.
All flashcards
What is an igneous rock?
A rock formed through the cooling and solidification of magma underground or lava at the surface.
What is the difference between magma and lava?
Magma is molten rock beneath Earth’s surface; when it reaches the surface, it is called lava.
What are three processes that can cause magma to form?
An increase in temperature, a decrease in pressure, and a change in composition, such as the addition of water.
How do igneous rocks help reveal Earth’s history?
Their chemistry can reveal source regions and formation conditions, their ages can be radiometrically measured, and their features can indicate tectonic settings.
Which igneous rocks are commonly associated with tungsten, tin, and uranium ores?
Granites and diorites are commonly associated with these ores; gabbros are more commonly associated with chromium and platinum ores.
Quiz questions
What texture commonly forms when magma cools slowly underground within insulating country rock?Answer: Coarse-grained phaneritic texture.
Which components are plotted on the TAS diagram to classify many volcanic rocks?Answer: Silica content and total alkali oxides.
What does porphyritic texture indicate about a rock’s cooling history?Answer: Large crystals formed before the remaining melt cooled more quickly.
How can water released from descending oceanic lithosphere promote volcanism at subduction zones?Answer: It lowers the solidus of the overlying mantle and helps it melt.
How can fractional crystallization change the composition of a magma?Answer: Separating early crystals can change the composition of the remaining melt.
Based on the Wikipedia article Igneous rock, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.