6.2 I GNEOUS R OCKS

I GNEOUS R OCK F ORMATION Igneous rocks are classified as: Felsic – Thick and slow moving magma. Contains Silica, Ca, Fe and Mg Forms light colored quartz and orthoclase feldspar

I GNEOUS R OCK F ORMATION Igneous rocks are classified as: Mafic: Formed from hotter, thinner and more fluid. Contains large amounts of Fe, Mg and low amounts of silica. Forms darker rocks.

I GNEOUS R OCK F ORMATION Underground Magma Forms Intrusive Rocks Cools slowly Has coarse surfaces Produces larger crystals within the rock.

I GNEOUS R OCK F ORMATION Magma Above the Surface (Lava) Forms Extrusive Rocks Cools Quickly Forms Microscopic/no crystals May form porphyry (large crystals surrounded by fine grained rock)

I GNEOUS R OCK F ORMATION Igneous Rock Description Granite Family Felsic Coarse (Intrusive) Makes up most of the continental crust Only visible after upward expansion. Other examples: Pumice and Obsidian

I GNEOUS R OCK F ORMATION Igneous Rock Description Gabbro Darker Dense

I GNEOUS R OCK F ORMATION Igneous Rock Description Diorite Family Grays and greens Coarse Grained

I GNEOUS R OCK F ORMATION Igneous Intrusion What is an igneous intrusion? A rock mass that cools inside the Earth’s interior (Pluton). These include: Dikes – Vertically cooled igneous rock Sills – Horizontally cooled igneous rock (b/t rock layers)

I GNEOUS R OCK F ORMATION Igneous Intrusions Batholiths Largest plutons Made of granite or granordiorite The cores of many mountain ranges Exposed through upward expansion Laccoliths Magma that bulges upwards into domes