Igneous Rocks

Front

What are igneous rocks?

Back

Igneous rocks are formed from the solidification of molten rock material (magma or lava). They can be classified into two main types: intrusive (plutonic) and extrusive (volcanic).

Front

What is the difference between intrusive and extrusive igneous rocks?

Back

Intrusive igneous rocks form below the Earth's surface from slowly cooled magma, resulting in larger crystals (e.g., granite). Extrusive igneous rocks form on the Earth's surface from rapidly cooled lava, resulting in smaller crystals (e.g., basalt).

Front

What does grain size indicate about the formation environment of igneous rocks?

Back

Grain size indicates the cooling rate of the magma or lava. Larger grains (1-10 mm) suggest slower cooling below ground (intrusive), while smaller grains (<1 mm) suggest rapid cooling above ground (extrusive).

Front

What is Bowen's Reaction Series?

Back

Bowen's Reaction Series is a conceptual model that illustrates the order of crystallization of minerals from cooling magma, showing how different minerals form at different temperatures.

Front

What is the significance of the texture of igneous rocks?

Back

The texture of igneous rocks, such as glassy, coarse, or vesicular, provides information about the cooling history and environment of the rock.

Front

What does a glassy texture in igneous rocks indicate?

Back

A glassy texture indicates rapid cooling of lava, preventing the formation of crystals, resulting in a smooth, glass-like appearance (e.g., obsidian).

Front

What is a vesicular texture in igneous rocks?

Back

A vesicular texture is characterized by the presence of small gas bubbles trapped in the rock, indicating that the lava was foamy and gas-rich during solidification (e.g., pumice).

Front

What is the role of silica in igneous rocks?

Back

Silica content influences the viscosity of magma and the type of igneous rock formed. High silica content leads to more viscous magma and typically results in explosive volcanic eruptions.

Front

What are the main components of magma?

Back

Magma is composed of molten rock, dissolved gases (such as water vapor, carbon dioxide), and solid crystals (minerals).

Front

How does cooling rate affect crystal size in igneous rocks?

Back

Slower cooling rates allow larger crystals to form, while rapid cooling results in smaller crystals. This is why intrusive rocks have larger crystals than extrusive rocks.