Physical Geology Igneous Rocks

Important Terminology  Magma  Molten rock below Earth’s surface  Lava  Molten rock at Earth’s surface  Pyroclastics  Solids erupted at Earth’s surface

Important Terminology  Extrusive  Formed above Earth’s surface  Also referred to as volcanic  Made of small crystals that cooled rapidly

Important Terminology  Intrusive  Formed below Earth’s surface  Also referred to as plutonic  Made of large crystals that cooled slowly

Classification  Composition  Ultramafic  Very heavy, dark minerals  Mafic  Heavy, dark minerals (Fe and Mg)  Intermediate  Mixture of heavy and light minerals  Felsic  Lighter in color and density (K, Al, and Na)

Classification  Glassy  Example: Obsidian  Exhibits Conchoidal fracture  Vesicular  Example: Pumice & Scoria  Bubbly texture caused by escaping gas

Classification  Crystalline  Aphanitic (fine grained crystals)  Phaneritic (coarse grained crystals)

Basic Igneous Rocks Classification FelsicIntermediateMaficUltramafic PhaneriticGraniteDioriteGabbroPeridotite AphaneticRyoliteAndesiteBasalt Komotite ( Only formed in Archean (no current examples!) ) Glassy/ Vesicular Obsidian Pumice Scoria

Felsic Rocks  Ryolite  Aphanetic, Volcanic Rock  Lava Domes cause this type of rock  Very dangerous!  Ex: Mount St. Helens’ lava dome

Felsic Rocks  Granite  Phaneritic, Plutonic Rock  Magma chamber cools and solidifies  Erosion reveals the rock below  Ex: Elephant Rocks

Intermediate Rocks  Andesite  Aphanetic, Volcanic Rock  Composite Cones/Stratovolcanoes formed this type of rocks  Andesitic lava and pyroclastic layers form this volcano  Ex: Mount Mayon and Mount Shasta

Intermediate Rocks  Diorite  Phaneritic, Plutonic Rock  Magma chamber cools and solidifies  Erosion reveals the rock below  Ex: France (St. Quay)

Mafic Rocks  Basalt  Aphanetic, Volcanic Rock  Shield volcanoes cause this type of rock  Very low viscosity  Ex: Mauna Loa

Mafic Rocks  Gabbro  Phaneritic, Plutonic Rock  Magma chamber cools and solidifies  Erosion reveals the rock below  Ex: Michigan Waterfall

Ultramafic Rocks  Komotite  Aphanetic, Volcanic Rock  Mainly restricted to the Archean age  Andesitic lava and pyroclastic layers form this volcano  Ex: Island of Gorgona on the Caribbean Oceanic plate off the Pacific coast of Colombia

Ultramafic Rocks  Peridotite  Phaneritic, Plutonic Rock  Magma chamber near the mantel cools and solidifies  Erosion reveals the rock below  Ex: Ocean Ridges where the rock is forced upward