AIM: How do
Rocks Tell Stories?
Do Now: What are the three different types of rocks? How are they
formed?
Igneous rocks …
formed from cooling
and solidification of
lava or magma
Rock Classification – 3 major
groups based on their methods of
formation or origin
Rock Types
• Sedimentary
rocks …
from compacted
and cemented
sediments, or
chemical
precipitates or
evaporites
• Metamorphic
rocks-
meta = change
morphic = form
rocks changed by
heat and pressure
–but remain solid
IGNEOUS ROCKS
Magma – molten material
BELOW the surface of the
Earth
Lava – molten material
AT OR ABOVE earth’s
surface
MAGMA VS. LAVA
VOLCANO - landforms generated when lava is
released from the Earth’s interior through
openings.
EXTRUSIVE FEATURES
Magma Intrusive
Features - Plutonic
Classification of Igneous Rocks
by Texture
• WHAT IS TEXTURE?
It is not how it feels
SIZE OF MINERAL CRYSTALS
INTERGROWN SILICATE
CRYSTALS - RANDOM PATTERN
What controls texture?
How fast an igneous rock
cools.
What controls how fast an igneous
rock cools?
Where the rock is formed.
coarser crystals
slower cooling
deep in ground
EXTREMELY SLOW COOLING HAS
ABNORMALLY LARGE CRYSTALS
AND IS VERY COARSE.
INTRUSIVE – MAGMA
Granite Rhyolite Figure 4.7 A MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
INTRUSIVE EXTRUSIVE
Diorite Andesite
Figure 4.7 B
MINERAL COMPOSITION THE SAME ---- TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
INTRUSIVE EXTRUSIVE
Gabbro Basalt MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
INTRUSIVE EXTRUSIVE
SEDIMENTARY ROCKS
Sedimentary Rocks
• 80 % of Earth’s surface is covered
with sediments and Sedimentary
Rocks
What is sediment????
Broken pieces of rocks called CLASTS
Chemical precipitates ( dissolved solids
come out of solution)
Organic fragments – shells, decayed
plant matter – this is called BIOCLASTIC
Source of Sediment
When Igneous, Metamorphic Rocks, and
Sedimentary Rocks are uncovered and exposed
to the atmosphere and hydrosphere they start to
break down
Weathering is the general term for all actions
that break down or wear away rock
Erosion is the carrying away of the sediment
The four steps to the formation of
sedimentary rocks are:
1. Deposited in horizontal layers
called beds or strata
2. Buried
3. Compacted – particles forced
extremely close together because
of the pressure of the overlying
layers and water
4. Cemented – glued together
Sedimentary Rocks Sediments that are
eroded settle to the bottom of the rivers, lakes, and oceans
Layer after layer of eroded earth is deposited on top of each other
Sand Composition Varies BUT TO BE
CONSIDERED SAND THE GRAIN SIZE IS
BETWEEN 0.2 -0.006 CM.
Breccia
Sediments
are
pebbles,
cobbles,
and
boulders
rounded
angular
Sand (0.2 to 0.006 cms.)
SANDSTONE
Silt (0.006 to 0.0004 cms.
SILTSTONE
Clay (less than 0.0004 cms.)
SHALE
ROCK SALT
DOLOSTONE
ROCK GYPSUM
Intergrown
crystals of just
1 mineral
BIOCLASTIC LIMESTONE CHEMICALLY PRECIPITATED
LIMESTONE
COAL
Cretaceous Limestone Deposits in Kansas
HORIZONTAL LAYERS
METAMORPHIC ROCKS
METAMORPHIC ROCKS META = CHANGE MORPH = FORM
Called the “Cinderella Rock”
Start with pre-existing rock
and change to another rock –
but these changes occur in the
SOLID STATE
METAMORPHISM
Process by which igneous,
sedimentary, or another
metamorphic rock called the
“parent rock” undergoes
changes in minerals and
texture
METAMORPHISM
Occurs in rocks due to the
effects of
• High temperature
• High pressure
HEAT EFFECTS
Temperature increases with depth or contact with magma
Random
arrangement
of minerals
Organized
arrangement of
minerals - banding
METAMORPHIC ROCK MANTRA
• INTERGROWN CRYSTALS
IN AN ORGANIZED
PATTERN
FOLIATED METAMORPHIC ROCKS
MICA
CRYSTALS
BECOME
LARGE
AND
SPANGLY
MICA SCHIST WITH GARNET
DEFORMED GNEISS
SANDSTONE METAMORPHOSES INTO QUARTZITE