Chapter 4
Rocks

Why should I care?
You’ve just been
abducted by aliens!!!
They’ve abandoned you on another planet. NOW
WHAT?!?!?!
What do I use to chop down trees with to build
my new fortress?
BUILD AN AXE… BUT HOW?
What kinds of rock will work?
 What can I do to make the axe?
 What else can I use rocks for?!?!?!


But first……..
WHAT IS A ROCK?
It
is a hard substance that is
made of one or more minerals
MAJOR ROCK GROUPS
 Rocks
are classified according to
how they are formed.
1. Igneous Rocks –
“fire formed”
2. Sedimentary Rocks “sediment rocks”
3. Metamorphic Rocks “changed rock”
ROCK CYCLE
 The
natural process of one rock type
changing into another rock type.
Melting
Cooling &
Crystallizing
Magma
Metamorphic
Rock
Igneous
Rock
Heat,
Pressure,
& Chemical
Reactions
Erosion &
Weathering
Sedimentary
Rock
Cementing &
Compacting
Sediment
IGNEOUS ROCKS
 Rocks
that are formed from magma
(below) or lava (above)
 Make up a large portion of the crust.
IGNEOUS CLASSIFICATION
 Based
on composition and texture.
1. TEXTURE
 the
size, shape, & relationships of the
mineral crystals in a rock
a. Coarse Grain - large crystals
Granite
Diorite
b.
Fine Grain - small crystals
Basalt
Rhyolite
c. Vesicular - full of holes because of
gas bubbles
Basalt
Pumice
d. Glassy - cools too fast to form
Scoria
crystals
Obsidian
e. Pyroclastic – cemented
volcanic ash, cinders, & bombs
Pumice
2. COMPOSITION
 Magma will cool and form mineral
crystals at different temperatures.
 Geologists
can identify igneous rocks
based on the specific minerals in the
rock.
Ж
Igneous rocks with fine grain texture
are made from lava
(Extrusive).
ж
Igneous rocks with coarse grain
texture are made from magma
(Intrusive).
SEDIMENTARY ROCKS
 Rocks
formed by the cementing &
compacting of small rock particles.
HOW ARE THEY FORMED?
1. As rocks are broken down by water
& wind (weathering/erosion,) the rock
particles (sediment) will sink to the
bottom of a water source.
2. Over a long period of time the
sediment will build up in layers. The
upper layers cause pressure on the
lower layers (compacting.)
------physical process
Pressure =
compacting
3. In other cases, chemicals within the
sediment will “glue” the sediment
together forming a rock (cementing.)
-----chemical process
SEDIMENTARY CLASSIFICATION
 Grouped based on how the rock was
formed & where the sediment came
from.
1. CLASTIC ROCK (DETRIAL)
 Sedimentary rocks that are made of
previously existing rock fragments.
 These rocks are named based on the
size & shape of the rock fragments
within the main rock.
EX: Sandstone & Shale
Sandstones
Breccia
Shales
Conglomerate
2. NON-CLASTIC ROCK (CHEMICAL)

Includes rocks that were formed
as a result of mineral crystallization
when water evaporated.
Ex: rock salt
 Includes
organic rocks such as coal &
fossils
 Includes
cavernous rocks such as
stalactites & stalagmites.
 Includes
microcrystaline quartz rocks
EX:
Limestone & Flint
Limestones
Flint/Chert
METAMORPHIC ROCKS

A rock that has changed in form
because of heat, pressure, and/or
chemical reactions.
HOW DOES THE ROCK CHANGE?
 When
a rock goes through a change it
is called metamorphism.
 Metamorphism can affect igneous
and/or sedimentary rocks that are deep
within the crust.
 Heat
will cause the minerals within the
rock to break down to form more heat
resistant minerals.
 Pressure will force the minerals to
rearrange themselves.
 Chemicals
within the rocks can alter or
change the chemical make-up of the
rock.
Shale----------Slate
Granite----------Gneiss
Limestone--------Marble
METAMORPHIC CLASSIFICATION
 Based on the arrangement of the
grains within the rock.
1. FOLIATED
 Metamorphic
rocks that have mineral
crystals arranged in parallel layers or
bands.
 The rock tends to break along the
bands.
EX:
Schist, Gneiss, & Slate
2. NON-FOLIATED
 Metamorphic
rocks that are NOT
banded and do NOT break into layers.
EX:
Marble
Marble & Quartzite
Quartzite
DESERTED ISLAND….OH NOES!!!!
How are rocks
my friend in
this situation?
Things I need to live:
1.
To Do list:
1.