Igneous Rocks

Pictures courtesy of Univ of Texas Geology Dept.


Let's review some terms on Igneous Rocks:

• Intrusive rocks- those that form from cooling magma beneath the Earth's surface (ex. granite, picture on left), they will have a course-grained texture.
• Extrusive rocks- those that form from magma that has reached the Earth's surface, lava, they will have a fine- grained texture ( ex. basalt, picture on right).
• Granitic- light colored rocks contain greater amounts of feldspar (felsic).
• Basaltic- dark colored rocks contain greater amounts of magnesium (mafic).
• Porphyritic- type of rock that has two different crystal sizes.
• Remember, igneous rocks are characterized by composition and texture.