1. Igneous Rock

2. Igneous Rocks
Igneous means “born of fire”.

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

4. 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

5. Formation of Igneous Rocks
Two Types of Igneous Rock:
Plutonic Igneous Rock (intrusive)
Volcanic Igneous Rock (extrusive)

6. 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)
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7. 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

8. 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

9. 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.

11. 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

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

13. 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

17. 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

18. 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).

19. 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.