Download Igneous Rock PPT notes

IGNEOUS ROCKS
I.
Igneous rocks are formed from
molten material.
- The term igneous is derived from Latin
term meaning “from FIRE”!!
ENVIRONMENT
A. Extrusive igneous rocks are formed when molten
rock cools above ground. Usually they are formed
after the material has been erupted by a volcano.
1. This molten material
cools quickly.
2. No crystals are visible
to the eye.
B. Intrusive igneous rocks are formed when
molten rock cools below ground.
1. These rocks cool
very slowly.
2. There is lots of
time for visible
crystals to grow
EXTRUSIVE
Cools quickly
Cools above ground
No visible crystals
INTRUSIVE
Cools slowly
Cools below ground
Visible crystals
TEXTURE
• Coarse:
– INTRUSIVE igneous rock
composed of large mineral grains.
• GRANITE
TEXTURE
• Fine:
– EXTRUSIVE igneous rock
composed of fine-grained minerals.
• BASALT
TEXTURE
• Glassy:
– HIGHLY VISCOUS, silica-rich
magma cools rapidly, no crystals.
• OBSIDIAN
TEXTURE
• Vesicular:
– HIGHLY VISCOUS, large amount of
dissolved gases, rock full of holes.
• PUMICE
COMPOSITION
• Mafic:
– Low silica
– Rich in Iron and Magnesium
• DARK COLOR.
• BASALT
COMPOSITION
• Felsic:
– High silica
• LIGHT COLOR.
• RHYOLITE
Igneous Rock Structures
• Intrusions vs. Extrusions:
- Form
Underground
- Form on
the surface
of the Earth
INTRUSIONS
• Batholiths:
– At least 100 km2 of surface exposure.
• Means “Deep Rock”
• Sierra Nevada Mountains
Exposed Batholiths
INTRUSIONS
• Laccoliths:
– Flat-bottom intrusion that pushes overlying rock layers into an arc.
• Means “Lake of Rock”
• Black Hills
–South Dakota
• Stocks:
INTRUSIONS
– Like a Batholith, but covers less than
100 km2.
• Devils Tower
–Wyoming
• Dikes:
INTRUSIONS
– Igneous intrusion that cuts across rock
layers.
• Black Canyon
–Colorado
• Sills:
INTRUSIONS
– Hardened magma formed between
parallel layers of rock.
• Salisbary Crags
–Scotland
EXTRUSIONS
• Volcanic Necks:
– Solidified central neck of a volcano.
• Shiprock
–New Mexico