Magma vs. Lava:
* Magma: Molten rock found beneath the Earth's surface.
* Lava: Magma that has erupted onto the Earth's surface.
Formation Process:
1. Melting: Rocks deep within the Earth melt due to heat and pressure. This molten rock is called magma.
2. Cooling and Solidification: As magma cools, it crystallizes, forming minerals. This process can happen:
* Intrusively: Magma cools slowly underground, forming large crystals and creating intrusive igneous rocks (e.g., granite).
* Extrusive: Lava cools rapidly on the Earth's surface, forming small crystals or even a glassy texture. This creates extrusive igneous rocks (e.g., basalt).
Characteristics of Igneous Rocks:
* Crystalline Texture: Igneous rocks are typically composed of interlocking crystals. The size of the crystals depends on the cooling rate.
* Composition: They are made up of various minerals, with common ones being feldspar, quartz, mica, and pyroxene.
* Color: The color of igneous rocks can vary widely, depending on the minerals present. For example, granite is usually light-colored, while basalt is dark.
* Density: Igneous rocks are generally denser than sedimentary rocks.
Types of Igneous Rocks:
* Intrusive (Plutonic) Rocks: Formed from magma that cooled slowly beneath the surface (e.g., granite, diorite, gabbro).
* Extrusive (Volcanic) Rocks: Formed from lava that cooled rapidly on the surface (e.g., basalt, rhyolite, andesite).
Examples of Igneous Rocks:
* Granite: A light-colored, coarse-grained intrusive rock.
* Basalt: A dark-colored, fine-grained extrusive rock.
* Obsidian: A glassy, volcanic rock formed from rapidly cooling lava.
* Pumice: A light-colored, porous volcanic rock formed from frothy lava.
Importance of Igneous Rocks:
* Building Materials: Granite and basalt are commonly used in construction.
* Source of Minerals: Igneous rocks can contain valuable minerals like gold, silver, and copper.
* Geological Insights: Igneous rocks provide clues about the Earth's interior and volcanic activity.
