Magmatic Petrology and Igneous Rock Classification

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Quel type de roches ignées solidifient lentement sous la surface de la Terre?

Roches intrusives

Quel type de roches ignées se forment rapidement à la surface de la Terre?

Roches extrusives

Quel est un exemple de roche intrusive?


Qu'est-ce qui caractérise les roches extrusives en termes de vitesse de refroidissement?

Refroidissement rapide

Quels types de roches sont généralement classés en tant que roches plutoniques?


Pourquoi les roches plutoniques ont tendance à former des cristaux plus gros?

En raison d'un refroidissement lent

Quelle est la principale différence entre les roches intrusives et les roches extrusives ?

Les roches intrusives se forment à l'intérieur de la croûte terrestre tandis que les roches extrusives se forment à la surface.

Quelles sont les principales caractéristiques du granite ?

Roche intrusive grossière, légère, composée de quartz, feldspath et mica.

Quelle est la principale caractéristique du basalte ?

Roche extrusive fine, sombre, composée d'oxyde de fer, d'olivine et de pyroxène.

Quelle méthode de classification des roches ignées est basée sur la distribution granulométrique ?

L'échelle de Wentworth

Quels sont les principaux minéraux constituants de la rhyolite ?

Quartz, feldspath, mica ou hornblende

Quelle est la principale caractéristique des diorites ?

Roches intrusives à grains moyens composées de plagioclase, pyroxène ou amphibole, et quartz ou hornblende.

Study Notes

Magmatic Petrology and Igneous Rock Classification

Magmatic petrology is a branch of geology focused on studying the origins, properties, and behaviors of magma, the molten material beneath the Earth's surface. This discipline provides valuable insights into various aspects of one of the planet's most dynamic systems, including its generation, evolution, and solidification. Within this field, there exists a crucial yet specific area of interest: the classification of igneous rocks. These rocks, which are classified based on their physical and chemical attributes, play a critical role in understanding the geological history of the Earth.

Igneous Rock Classification

To classify igneous rocks, several criteria are used, such as their parent magmas' composition, texture, and size distribution. Generally speaking, two main categories exist within the realm of igneous rocks: intrusive (also referred to as plutonic) and extrusive (often called volcanic).

  1. Intrusive (Plutonic) Igneous Rocks: These rocks solidify slowly beneath the Earth's surface, which allows larger crystals to form. Due to their slow cooling rates, minerals have sufficient time to grow before the rock cools and solidifies completely. Plutonic rocks typically occur in large bodies and form over extended periods. Some examples include granites and diorites.

  2. Extrusive (Volcanic) Igneous Rocks: Conversely, extrusive rocks do not have enough time to crystallize extensively before they reach Earth's surface. As a result, they exhibit smaller mineral grains. These rocks tend to be formed rapidly and cool quickly due to contact with the atmosphere, water, or ice. Common examples include basalt and rhyolite.

Characteristics of Intrusive (Plutonic) Rocks


Granites are coarse-grained, light-colored igneous rocks that typically contain quartz, feldspar (both orthoclase and albite), and mica minerals. They often form large bodies within the continental crust through slow crystallization processes associated with the intrusion of magma into pre-existing rock formations.


Diorites are medium-grained igneous rocks composed primarily of plagioclase feldspars, pyroxene or amphibole, and quartz or hornblende. These rocks can be found beneath the Earth's surface in both the oceanic lithosphere and the continental crust.

Characteristics of Extrusive (Volcanic) Rocks


Basalts are dark-colored volcanic rocks characterized by their fine-grained texture, which results from rapid cooling. They usually consist mainly of iron oxide (magnetite), olivine, and pyroxene minerals, along with other minor constituents such as glassy, siliceous material.


Rhyolites are light-colored volcanic rocks with coarse crystals. They typically contain quartz, feldspar (both orthoclase and albite), and other minerals such as mica or hornblende. These rocks solidify quickly due to rapid cooling, often forming domes or cones at volcanic sites.

Classification Methods

Several methods have been developed to categorize igneous rocks based on their physical properties. For instance, the Wentworth scale classifies rock particles according to size distribution, while the Lindgren classification uses mineral composition to distinguish various types of intrusive and extrusive rocks. Another common approach involves dividing rocks into silicate and non-silicate categories based on their primary mineral component.

In summary, magmatic petrology plays a significant role in understanding the formation and behavior of igneous rocks, which are classified based on factors like parent magma composition, texture, and size distribution. By studying these elements, scientists gain crucial insights into Earth's geological history and processes.

Explore the fascinating world of magmatic petrology, which delves into magma's properties and behaviors beneath the Earth's surface. Learn about the classification of igneous rocks based on factors like parent magma composition, texture, and cooling rates, providing crucial insights into Earth's geological history.

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