Chapter 3 Rocks
Why study rocks?
- rocks tell the story of your location
EX: Indiana is made of mostly limestone = formed in a
shallow marine setting = so in the past Indiana was
under water
How is a rock different than a mineral?
Rock = a naturally occurring combination of minerals
 Rock will show some of the properties of the minerals that
make it up
EX: Limestone is made of mainly calcite so it
reacts to acid
3 Types of Rocks:
1. Igneous = rock made from cooled magma
either above or below ground
EX: Granite
2. Sedimentary = rock formed from compacted
& cemented sediments
EX: Limestone
3. Metamorphic = a rock that has been
changed (cooked) by increasing temperature
and/or pressure to form a new rock
EX: Marble
 Rocks are continually changing
from one type to another =
Rock Cycle
Igneous Rocks:
• Formed from cooled magma
• Can form at 2 locations:
1. Below Ground = Intrusive
- slow cooling of magma because
ground is insulating = this allows
grains/crystals to grow large
 Coarse Grained Texture
2. Above Ground = Extrusive
- quick cooling = no time for
crystals to grow so extrusive
rocks have small grains
 Fine Grained Texture
igneous
Igneous Rock Fine Grained Texture Cont…
- HOWEVER……..Exceptionally quick cooling above ground can
give special textures:
A. Glassy = lava instantly cooled
by seawater = No grains in rock
 Very smooth/glassy feel
EX: Obsidian
B. Pyroclastic Texture = magma cooled instantly by being
shot into the air (i.e. volcano)
 rock has air pockets and very rough feel
EX: Pumice & Scoria
How do you classify
Igneous Rocks?
1. Texture = Coarse, Fine, Glassy,
Pyroclastic
2. Mineral Composition = color of rock
A. Light = white, clear, light pink, light gray
B. Intermediate = equal parts black & white
(salt & pepper) or dark pinks and dark grays
C. Dark = Black
Igneous Rock Identification
Chart
MINERAL COMPOSITION
T
E
X
T
U
R
E
S
Dark
Intermediate
Light
Coarse
Gabbro
Diorite
Granite
Fine
Basalt
Andesite
Rhyolite
Glassy
Obsidian
Obsidian
----------
Pyroclastic
Scoria
Scoria
Pumice
Sedimentary Rocks:
• Formed from compacted/cemented
sediments
– Weathering = process that breaks down
rocks into sediments
– Compaction = process that squeezes or
compacts sediments
– Cementation = process where smaller
dissolved minerals are deposited between
sediments/rocks “glues” pieces together
2 Types of Sedimentary Rocks:
1. Clastic = made of
weathered & broken
pieces of rock
2. Chemical = form when
dissolved minerals precipitate (separate)
from water
EX: lake totally dries
up during the summer
How are Sedimentary
Rocks classified?
1. Type = Clastic vs. Chemical
2. Texture = grain size (coarse  fine)
3. Composition = minerals
(chemical sed. rocks only)
Sedimentary Rock Identification Charts
Clastic Sedimentary Rocks
Texture
Rock Name
Coarse/Gravel
Conglomerate
Medium/Sand
Sandstone
Fine/Mud
Shale
Chemical Sedimentary Rocks
Composition
Texture
Rock Name
Calcite
Very Coarse
Coquina
Calcite
Coarse
Fossiliferous
Limestone
Calcite
Medium
Limestone
Gypsum
Fine
Rock Gypsum
Halite
Fine
Rock Salt
Organic Matter
Medium/Fine
Coal
Metamorphic Rocks:
• Form when pre-existing rocks
are changed by heat and/or
pressure
– Occurs during mountain building,
volcanic activity, etc…
2 types of Metamorphic Rocks
1. Contact = when magma forces its way into
cracks/ layers of rock
- Rise in Temperature only
- Small changes to surrounding rocks
2. Regional = occurs during large scale
mountain building
(EX: 2 continental plates colliding)
- Extreme rise in Temperature & Pressure
- Large changes to surrounding rock
- Rock usually becomes layered
How are Metamorphic Rocks
classified?
1. Composition of parent material
2. Texture = layered vs. non-layered
 The longer a rock is metamorphosed, the
more layered its appearance
(i.e. the longer it has
been
cooked, the more
obvious layers it has)
Metamorphic Rock
Identification Chart
Parent Rock
Texture
Rock Name
Shale
Very Fine Layers
Slate
Slate
Fine Layers
Phyllite
Phyllite
Medium Layers
Schist
Schist
Coarse Layers
Gneiss
Limestone
NO Layers
Marble
Sandstone
NO Layers
Quartzite
Ch. 3 Final Assignment
Worth 25 points !
Pg. 89-90
1, 2, 4, 5, 8 = write out questions and answers
14, 17, 19, 21, 22 = write out answers only, in complete sentences
Vocabulary Words
Cementation
Chemical Sed. Rock
Clastic Sed. Rock
Compaction
Contact Met.
Extrusive
Igneous Rock
Intrusive
Metamorphic Rock
Pyroclastic
Regional Met.
Rock
Rock Cycle
Sedimentary Rock
Weathering
SS #8
Put the date and SS # 8 on your paper.
Copy the question & answer it.
What is the Rock Cycle?