Igneous Rock Types to Know for Earth Science

Igneous rocks form from cooled magma or lava, showcasing a variety of textures and compositions. Understanding these rock types, like granite and basalt, helps us grasp Earth's processes and the materials that shape our planet's surface and structure.

1. Granite

   • Coarse-grained, light-colored igneous rock primarily composed of quartz, feldspar, and mica.
   • Formed from the slow crystallization of magma beneath the Earth's surface.
   • Commonly used in construction and monuments due to its durability and aesthetic appeal.

2. Basalt

   • Fine-grained, dark-colored igneous rock rich in iron and magnesium.
   • Forms from the rapid cooling of lava at the Earth's surface, typically in volcanic regions.
   • Makes up much of the ocean floor and is a key component of volcanic islands.

3. Obsidian

   • Volcanic glass that forms when lava cools rapidly without crystallizing.
   • Characterized by its smooth, glassy texture and often dark color, though it can be found in various hues.
   • Historically used by humans for tools and weapons due to its sharp edges.

4. Pumice

   • Light, porous volcanic rock formed from lava that cools quickly and traps gas bubbles.
   • Often used as an abrasive material in beauty products and cleaning agents.
   • Can float on water due to its low density.

5. Andesite

   • Intermediate in composition between basalt and rhyolite, typically gray to brown in color.
   • Commonly found in volcanic arcs and associated with subduction zones.
   • Often exhibits a porphyritic texture, with larger crystals embedded in a finer-grained matrix.

6. Rhyolite

   • Light-colored, fine-grained igneous rock rich in silica, often containing quartz and feldspar.
   • Forms from the slow cooling of lava, similar to granite but at the surface.
   • Associated with explosive volcanic eruptions and can form extensive lava flows.

7. Gabbro

   • Coarse-grained, dark-colored igneous rock that is the intrusive equivalent of basalt.
   • Composed mainly of plagioclase feldspar and pyroxene, with a higher density than granite.
   • Typically forms in the lower crust and upper mantle, contributing to the formation of oceanic crust.

8. Diorite

   • Coarse-grained igneous rock with a composition between granite and gabbro, often speckled in appearance.
   • Contains a mix of light and dark minerals, primarily plagioclase feldspar and hornblende.
   • Forms from the slow cooling of magma beneath the Earth's surface, often in continental crust.

9. Scoria

   • Dark, vesicular volcanic rock that forms from the rapid cooling of lava with trapped gas bubbles.
   • Typically reddish-brown or black in color and lighter than basalt due to its porous nature.
   • Commonly used in landscaping and as a lightweight aggregate in construction.

10. Pegmatite

    • Coarse-grained igneous rock characterized by exceptionally large crystals, often containing rare minerals.
    • Forms from the crystallization of magma in the final stages of cooling, typically in pockets within granite.
    • Important source of gemstones and industrial minerals, such as lithium and beryllium.