Download What is a rock?

uniformitarianism:
1795 – James Hutton
“the present is the key to
the past”
we can learn about Earth’s
history by studying present
processes
What is a rock?
rock: an aggregate
(group) of minerals
3 Types of Rocks
igneous
sedimentary
metamorphic
Igneous Rock
a rock that forms when
melted rock inside the
Earth cools
Igneous rocks can form
on Earth’s surface or
deep inside Earth.
magma: molten rock inside
the Earth
intrusive: rocks that form beneath
Earth’s surface
- mineral grains are clearly seen
- form slowly (1000’s of years)
ex. granite
extrusive: rocks that form at
Earth’s surface
- no distinct mineral grains
- form relatively quickly
ex. obsidian
porphyry: rocks with
large crystals
surrounded by fine
crystals
Families of
Igneous Rock
Granite Family - light minerals
granite: coarse grained
rhyolite: fine grained
obsidian: glassy
pumice: spongy
Gabbro Family - dark minerals
gabbro: coarse grained
basalt: fine grained
basalt glass: glassy
scoria: spongy
Diorite Family: both light
and dark minerals
diorite: coarse grained
andesite: fine grained
Sedimentary Rock
a rock that forms from
pieces of other rocks
or the remains of onceliving things
Types of Sedimentary Rocks
clastic
chemical
organic
Clastic Rocks:
rocks that form from the
weathering of rocks that
already exist
- most clastic rocks are
formed from weathering from
running water
Dissolved minerals (natural
cements) settle into the
spaces between sand grains
and pebbles.
This “cement” binds the
fragments together
Ex. shale, sandstone,
conglomerate
Sorting of Sediments:
Chemical Sedimentary
Rocks
rocks that are formed when
minerals fall out of solution
(when water evaporates or by
chemical actions)
ex. chemical limestone; rock
salt
Organic Rocks
rocks that are formed from the
remains of plants and animals
ex. organic limestone; coal
• much of the rock found in
this area (PA) is limestone
stratification:
arrangement of rocks
in visible layers
Metamorphic Rock
A rock that is formed
when rocks that already
exist are exposed to
heat and pressure
Regional Metamorphism
definition: large areas
of rock are under
intense heat and
pressure
Examples of regional
metamorphism:
granite  gneiss
shale  slate  phyllite  schist
foliation: mineral grains
are flattened and lined
up in parallel bands
layers are easily
separated ex. slate
Contact Metamorphism
definition: hot magma
forces its way into
overlying rock and
changes it
-no foliation
ex.
shale  hornfels
sandstone  quartzite
limestone  marble
THE ROCK CYCLE
the process by which
Earth materials
change to form
different types of
rocks
Remember…
 Rocks become igneous
through melting and cooling
 Rocks become sedimentary
through weathering and
erosion
 Rocks become metamorphic
through heat and pressure