Igneous Rocks and Intrusive Activity

Igneous Rocks

• Formed by cooling and solidifying of molten materials.
• Can be classified as intrusive or extrusive based on their formation location.

Intrusive Rocks

• Also known as plutonic rocks.
• Formed from magma that cools slowly within the Earth's crust, leading to larger crystal sizes.
• Common types include granite and diorite.

Extrusive Rocks

• Form when magma erupts onto the Earth's surface as lava or ash.
• Typically cool quickly, resulting in small or no visible crystals.
• Examples include basalt, rhyolite, pumice, and obsidian.

Intrusive Bodies

• Created by magma injected into fractures or zones of weakness.
• Can lead to various geological formations.

Batholiths

• Large mass of intrusive rock covering over 100 square kilometers.
• Typically composed of granite or similar rocks.

Laccoliths

• Sheet-like intrusive bodies injected between sedimentary rock layers.
• The overlying rock is pushed upward, creating a dome shape.

Dikes

• Geologic bodies that cut across existing rock layers and structures.
• Often form in vertical or near-vertical orientations.

Sills

• Tabular sheet intrusions that lie parallel to pre-existing rock layers.
• Injected between older sedimentary rock or along foliations in metamorphic rock.

Andesite

• Intermediate extrusive rock between rhyolite and basalt.
• Characterized by moderate viscosity, forming thick lava flows and domes.

Pumice

• Light-colored, porous igneous rock resulting from explosive volcanic eruptions.
• Often has a frothy texture due to gas bubbles trapped during cooling.

Obsidian

• Volcanic glass formed from rapid cooling of felsic lava.
• Characterized by its glassy texture and often dark color.

Granite

• Light-colored igneous rock with visible grains.
• Composed mainly of quartz, feldspar, and minor minerals.
• Forms from slow crystallization of magma beneath the surface.

Country Rock

• Refers to the native rock surrounding plutons.
• Intrusive bodies like dikes can intersect and alter country rock.

Contact Metamorphism

• Occurs when a rock's mineralogy and texture change due to heat and pressure from nearby molten magma.

Felsic Rocks

• Rich in quartz and feldspar, typically lighter in color.
• Common felsic minerals include quartz and muscovite.

Mafic Rocks

• Rich in magnesium and iron, usually darker in color.
• Common mafic minerals include olivine, pyroxene, and biotite.

Feldspar

• Constitutes over half of the Earth's crust.
• Formed from aluminum, silica, oxygen, and potassium combinations.

Explore the fascinating world of igneous rocks with this flashcard quiz. Understand the formation of both igneous and intrusive rocks, their characteristics, and their origins. Perfect for geology enthusiasts or students studying Earth science!