6.2 IGNEOUS ROCKS

IGNEOUS ROCK FORMATION

Igneous rocks are classified as:

Felsic – Thick and slow moving magma.

Contains Silica, Ca, Fe and Mg

Forms light colored quartz and orthoclase feldspar

IGNEOUS ROCK FORMATION

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.

IGNEOUS ROCK FORMATION

Underground Magma Forms Intrusive

Rocks Cools slowly Has coarse

surfaces Produces larger

crystals within the rock.

IGNEOUS ROCK FORMATION

Magma Above the Surface (Lava) Forms Extrusive

Rocks Cools Quickly Forms

Microscopic/no crystals

May form porphyry (large crystals surrounded by fine grained rock)

IGNEOUS ROCK FORMATION

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

IGNEOUS ROCK FORMATION

Igneous Rock Description

Gabbro Darker Dense

IGNEOUS ROCK FORMATION

Igneous Rock Description

Diorite Family Grays and greens Coarse Grained

IGNEOUS ROCK FORMATION

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)

IGNEOUS ROCK FORMATION

Igneous IntrusionsBatholiths

Largest plutons Made of granite or granordiorite The cores of many mountain ranges Exposed through upward expansion

Laccoliths Magma that bulges upwards into domes