Rock Topics

Igneous Rocks

"Igneous" comes from the Latin word for fire, and refers to rocks that formed from molten material.  Igneous rocks can be extrusive or intrusive.  They are classified based on their texture and composition.


1. Extrusive and intrusive

2. Classification

3. Common igneous rocks

Extrusive and Intrusive (Part 1)

Extrusive Rocks

Extrusive igneous rocks form on the earth’s surface.

Lava flows form from volcanic eruptions.

Pahoehoe Pahoehoe lava flow (Photograph by Parvinder Sethi)

Glowing lava (Photograph by Parvinder Sethi)

Lava flows are a type of extrusive igneous rock.  This lava, from Hawaii, is called pahoehoe because of its smooth, shiny, ropy texture.