Rock Intro

 A rock is a naturally occurring solid

mixture of one or more minerals, or
organic matter

 Rocks are classified by how they

are formed, their composition, and
texture

 Rocks change over time through

the rock cycle

 Igneous rock begins as magma.

 Magma can form:

▪ When rock is heated
▪ When pressure is released
▪ When rock changes composition

 Magma freezes between

700 °C and 1,250 °C

 Magma is a mixture of
many minerals

http://www.fi.edu/fellows/payton/rocks/create/igneous.htm

 Felsic: light colored rocks that are rich in

elements such as aluminum, potassium,
silicon, and sodium

 Mafic: dark colored rocks that are rich in

calcium, iron, and magnesium, poor in silicon

 Coarse-grained: takes longer to cool, giving

mineral crystals more time to grow

 Fine-grained: cools quickly with little to no

crystals

Felsic

Mafic

Coarse-Grained

Fine-Grained

Granite

Gabbro

Basalt

Rhyolite

 Intrusive Igneous Rocks:

magma pushes into
surrounding rock below the
Earth’s surface

 Extrusive Rocks: forms when

magma erupts onto the Earth’s
surface (lava), cools quickly
with very small or no crystals
formed

http://www.windows.ucar.edu/tour/link=/earth/geology/ig_intrusive.html&edu=high&fr=t

Obsidian is a dark-colored volcanic glass that forms from the very rapid
cooling of molten rock material. It cools so rapidly that crystals do not form.

Is this rock Felsic or
Mafic?

Is it fine-grained or
coarse-grained?

Is this rock Intrusive or
Extrusive?

Mafic, fine grained, extrusive

http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

 Sedimentary rock is formed by erosion

 Sediments are moved from

one place to another

 Sediments are deposited in

layers, with the older ones

on the bottom

▪ The layers become compacted

and cemented together

▪ Sedimentary Rocks are formed at or near the

Earth’s surface

▪ No heat and pressure involved

▪ Strata – layers of rock

▪ Stratification – the process in

which sedimentary rocks are
arranged in layers

Clastic – made of fragments of rock
cemented together with calcite or quartz

Breccia is a term most often
used for clastic sedimentary
rocks that are composed of
large angular fragments
(over two millimeters in
diameter).

The spaces between the
large angular fragments can
be filled with a matrix of
smaller particles or a mineral
cement that binds the rock
together.

Chemical sedimentary – minerals crystallize
out of solution to become rock

Limestone is a sedimentary rock
composed primarily of calcium
carbonate (CaCO3) in the form of
the mineral calcite. It most
commonly forms in clear, warm,
shallow marine waters.

It is usually an organic
sedimentary rock that forms
from the accumulation of shell,
coral, algal and fecal debris.

Organic sedimentary – remains of plants and
animals

Coal is an organic
sedimentary rock that
forms from the
accumulation and
preservation of plant
materials, usually in a
swamp environment.

Coal is a combustible rock
and along with oil and
natural gas it is one of the
three most important
fossil fuels.

http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm

▪ Meaning to change shape

▪ Changes with temperature
and pressure, but remains
solid

▪ Usually takes place deep in
the Earth

 Contact Metamorphism – heated by nearby magma
 Increased temperature changes the composition of

the rock, minerals are changed into new minerals

Hornfels is a fine-grained non-foliated
metamorphic rock produced by
contact metamorphism

http://www.windows.ucar.edu/tour/link=/earth/geology/meta_contact.html&edu=h igh&fr=t

▪ Regional Metamorphism –

pressure builds up in rocks
that is deep within the Earth

▪ Large pieces of the Earth’s

crust collide and the rock is
deformed and chemically
changed by heat and pressure

http://www.windows.ucar.edu/tour/link=/earth/geology/meta_regional.html&edu=high&fr=t

 Foliated - contain aligned grains of flat

minerals

Gneiss is foliated
metamorphic rock
that has a banded
appearance and is
made up of granular
mineral grains.

It typically contains
abundant quartz or
feldspar minerals.

 Non-Foliated – mineral grains are not

arranged in plains or bands

Marble is a non-
foliated metamorphic
rock that is produced
from the
metamorphism of
limestone.

It is composed
primarily of calcium
carbonate.

 Determine if the following rock samples are

foliated or non-foliated:

Amphibolite

Quartzite
Phyllite

Foliated