IGNEOUS ROCK NOTES
I. What is a rock?
Rock - two or more
minerals (found in the
earth’s crust) bound
together in a solid form
II. Rock types
A. Sedimentary rocks- formed by
the hardening and cementing of
layers of sediment.
II. Rock types
B. Metamorphic rocks- formed when
rocks that already exist are changed by
heat and pressure into new kinds of
rocks.
II. Rock types
C. Igneous rocks- formed by
cooling and hardening of hot
molten rock from inside the Earth.
Hot molten rock from inside the
earth is called magma.
III. Igneous Rock Formation
A. Magma - molten (liquid) rock found
beneath the earth’s surface.
Intrusive Rock - rock formed underground
when magma cools
III. Igneous Rock Formation
A. From Magma (Intrusive )
Cooled slowly
Deep
Shallow
Large/Coarse Small
Crystals
Crystals
III. Igneous Rock Formation
B. Lava - magma on the surface of the earth
Extrusive Rock - rock formed on the
surface when lava cools
III. Igneous Rock Formation
B.From Lava (Extrusive)
Cooled quickly
Surface
Fine Crystals
Glassy Rocks
IV. Igneous Rock Characteristics
A. Felsic (feldspar and silica--Granitic, Continental)
•
Chemistry: High percent of silicates (Si)
and water. Low percent of iron (Fe),
calcuim (Ca), & magnesium (Mg)
•
Color: Light colored minerals
•
Viscosity: More viscous (Thick--Low
temperatures and slow flowing)
•
Trapped gases: H2O, O, CO2, H2, CO,
H2S, SO2
•
Density: Low level (high gas content)
•
Volcanic source: Explosive volcanoes,
and cinder cones
IV. Igneous Rock Characteristics
B. Mafic (Magnesium and iron--Basaltic, Oceanic)
• Chemistry: Low percent of silicates
(Si). High in Ca, Fe, Mg.
• Color: Dark colored minerals
• Viscosity:Low viscosity (thin--high
temperature and more fluid)
• Trapped gases: fewer present
• Density: Higher level (few gases)
• Volcanic source: “Gentle” eruption
volcanoes , form broad shield
volcanoes like Hawaii, ocean ridges
IV. Igneous Rock Characteristics
C. Andesitic (Intermediate, Continental)
•
Chemistry: Intermediate percent of
silicates (Si). Intermediate in Ca, Fe,
Mg.
•
Color: Intermediate colored minerals
•
Viscosity: Intermediate viscosity
(fluidity)
•
Trapped gases: Intermediate amounts
present
•
Density: Intermediate level
•
Volcanic source: Intermediate eruption
volcanoes
IV. Igneous Rock Characteristics (D. Review)
A. Felsic
Mostly light
colored minerals
[ Si]
[Ca, Fe, Mg]
B. Mafic
Mostly dark
colored minerals
[ Si]
[Ca, Fe, Mg]
C. Andesitic
Contain light and dark minerals
Intermediate levels of [Si, Ca, Fe, Mg]
IV. Igneous Rock Characteristics (D. Review)
A. Felsic
Dissolved
Gases
Thick & Slow
Hard For Gases
To Escape
Explosive Eruptions
B. Mafic Dissolved
Gases
Thin & Fast
Gases Escape
Easily
“Gentle” Eruptions
Note: Dissolved Gases Include H2O, S, CO2, H2, CO, H2S, SO2
IV. Igneous Rock Characteristics
D. Review
IV. Igneous Rock Characteristics (D. Review)
Lighter
colored
rocks
Darker
colored
rocks
Large
crystals
Small
crystals
NO
crystals
Intrusive
Extrusive
V. Plate Tectonics and Igneous Rocks
VI. How we study rocks
A. Color: Lightness/darkness indicates
chemistry. Darker rocks tend to
have more iron (Mafic), lighter
rocks have more silicon (Felsic).
B. Crystal size: Can be measured in
millimeters using a hand
lens/microscope and ruler.
Larger crystals need more
time to form and are found
in rocks that cool slowly
(intrusive).
Felsic
Fine
crystals
Andesitic
Small
crystals
Large
crystals
Mafic
VI. How we study rocks
C. Density: mass (g) ÷ volume (ml or cm3).
More dense rocks formed from magma
that originates deeper in mantle (less
explosive volcanoes) and contain fewer
gases (Mafic).
Less dense rocks formed from magma
that originates from outer mantle (more
explosive volcanoes) and contain more
trapped gases due to interaction with
ocean water (Felsic).
THE END