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: Plutonic Igneous Rock (intrusive) 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) 1200-2100 fahrenheit

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: Batholith Largest plutons Primarily granite Common in the interior of major mountain chains

Massive pluton that formed from a magma chamber Stocks Massive pluton that formed from a magma chamber About the size of a mountain Laccolith A mushroom-shaped pluton with a round top and flat bottom Occurs as a result of intense heat and pressure Stocks are massive plutons that formed from magma chambers.  Most stocks are about the size of  mountains, and each probably represents a single magma chamber that fed one or a few volcanoes. An example of a stock is the source of the granodiorite currently being quarried from Little Cottonwood Canyon south of Salt Lake City. Batholiths are also massive plutons, but are much larger than stocks. They probably formed and several different magma chambers are emplaced under a volcanic range--over time filling all the space between. Batholiths can span entire states--large states.  California's Sierra Nevada Range is a batholith.   The Idaho Batholith underlies the Snake River Plain.

Sill Forms when magma intrudes into parallel layers of rock Few centimeters – hundreds of meters in thickness 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).

Gold-bearing vein in Sierra Nevadas 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. Gold-bearing vein in Sierra Nevadas This fluid solidifies to form metal-rich quartz veins, such as the gold-bearing veins found in the Sierra Nevada mountains.