Igneous Rock Igneous Rocks Igneous means born of

Igneous Rock

Igneous Rocks • Igneous means “born of fire”.

Formation: • Formed when magma or lava cools and hardens through the process of crystallization • Crystallization = the formation of mineral grains

Main Characteristics: • Classified by texture (cooling rate) and composition (color) • Usually made of 2 or more minerals • Contains no fossils • Has no layering • Rarely reacts with acids • Can be light-colored to dark-colored • Can be fine-grained, coarse-grained, or glassy • Resistant to weathering

Formation of Igneous Rocks Two Types of Igneous Rock: 1) Plutonic Igneous Rock (intrusive) 2) Volcanic Igneous Rock (extrusive)

1. Plutonic Igneous Rock • Formed from magma within Earth • Magma is melted rock material composed of common elements and fluids • As magma cools, atoms and compounds in the liquid rearrange themselves into new crystals called mineral grains • Rocks form as these mineral grains grow together • Rocks that form from magma below the surface are called intrusive igneous rocks (PLUTONS)

• It takes a long time for these rocks to cool because they form at great depths and are surrounded by other rocks • Slowly cooled magma forms individual mineral grains that are large enough to be seen with the unaided human eye

• Plutons – name given to intrusive rock bodies • Plutons are classified by their size, shape, and relationship to surrounding rocks. Types of Plutons: a) Batholith • Largest plutons • Primarily granite • Common in the interior of major mountain chains

b) Stocks • Massive pluton that formed from a magma chamber • About the size of a mountain c) Laccolith • A mushroom-shaped pluton with a round top and flat bottom • Occurs as a result of intense heat and pressure

d) Sill • Forms when magma intrudes into parallel layers of rock • Few centimeters – hundreds of meters in thickness e) Dike • Pluton that cuts across pre-existing rock

Draw in and Label the Plutons (Igneous Intrusions) in Notes!

2. Volcanic Igneous Rock • Formed from lava at the surface • When lava cools at the surface, it is exposed to air and water and cools quickly • Quick cooling prevents mineral grains from growing large

Igneous Rocks as Resources: • Used as building materials WHY? • Interlocking mineral grains make igneous rocks strong • The minerals that they are made up of are more resistant to weathering

Igneous Rocks as Resources: • Ores – a metal-bearing mineral or rock that can be mined for a profit • Ores are often associated with igneous intrusions (magma that cools into rock inside Earth). • Fluid left during magma crystallization contain high levels of silica, water, and any leftover elements that were not included into the common igneous minerals (gold, lead, silver, copper).

• These elements along with the dissolved silica are released at the end of magma crystallization in a hot, mineral-rich fluid that fills cracks and voids in the surrounding rock. Goldbearing vein in Sierra Nevadas