All rocks are heavy.
True or False
A heavy piece of rock?
Think again!
All rocks are hard.
True or False
False
• Chalk
• Pumice
• Talc
Rocks never change.
True or False
False
• Rocks are changed by processes such as:
– Melting
– Pressure
– Heat
– Weathering and Erosion
Minerals
• A mineral is a naturally formed solid
that has a repeating threedimensional structure.
• Minerals are the building blocks that
make up rocks.
By asking the four questions you
can tell if something is a mineral.
1. Is it nonliving material?
A mineral is inorganic, meaning it isn’t made of or by
living things.
2. Is it formed in nature?
Crystalline materials made by people aren’t classified
as minerals.
Minerals are not formed by plants or animals.
3. Is it a solid?
Minerals can’t be gases or liquids.
4. Does it have a crystalline structure?
Minerals are crystals, which have a repeating inner
structure that
determines the shape of the crystal.
If you cannot answer “yes” to all four
questions, you don’t have a mineral.
• A crystal is a solid substance in which the
atoms are arranged in a repeating pattern
in three dimensions.
• Each mineral has a crystalline structure
that depends on the elements that make
up the mineral. The arrangement of the
atoms within the crystal creates the
crystal’s shape.
Types of Minerals
Minerals are divided into two groups based on
the elements they are made of:
1 Minerals that contain the elements silicon and
oxygen are called silicate minerals.
2 The nonsilicate minerals do not contain a
combination of the elements silicon and oxygen.
Minerals in this group are made up of other
elements, such as carbon, oxygen, iron, and
sulfur.
Identifying Minerals using 7
physical properties
1. Color - Small amounts of impurities can
change a mineral’s color
2. Luster - the way the surface of a mineral
reflects light. Minerals have metallic,
sub- metallic, or nonmetallic luster.
3. Streak -the color of a mineral in
powdered form. When a mineral is
rubbed against a hard plate, the mark left
behind is the streak.
4. Cleavage and Fracture - is the
tendency of some minerals to
break along flat surfaces. The way
that a mineral breaks is
determined by the arrangement of
its atoms.
5.Hardness - a mineral’s resistance
to being scratched. Scientists use
Mohs hardness scale to compare
the hardness of minerals.
6.Density - is the measure of how
much matter there is in a given
amount of space.
7. Special properties
• Fluorescence—Calcite and fluorite glow under
ultraviolet light.
• Chemical reaction—Calcite will “fizz” when a
drop of weak acid is placed on it.
• Optical properties—A thin, clear piece of
calcite placed over an image will cause a double
image.
• Taste—Halite has a salty taste.
• Magnetism—Magnetite and pyrrhotite are both
natural magnets that attract iron.
• Radioactivity—Minerals that contain radium or
uranium can be detected by a Geiger counter.
Review questions
1.How do you
determine a minerals
streak?
• By scraping the mineral across
a ceramic streak plate. The
color of the material that rubs
off the mineral sample is the
mineral’s streak.
2. What is the
difference between
cleavage and
fracture?
If a mineral has cleavage, it breaks along
flat surfaces.
Fracture is the way a mineral breaks along
curved or irregular surfaces
See page 397 of text for picture
Minerals Combine to Form
Rock
• Rock is a solid mixture of crystals of one or more
minerals.
• The main classification of rock depends on how
the rock formed.
1. Igneous rock forms when hot, liquid rock,
(magma) cools and hardens.
2. Sedimentary rock forms when pieces of rocks
or minerals are compacted or cemented
together.
3. Metamorphic rock forms when existing rock is
heated and squeezed deep inside the Earth.
Each of the three types of
rock is further classified by
composition and texture.
• The composition of a rock is its chemical
makeup, or the combination of minerals from
which the rock is made.
• The texture of a rock is determined by the sizes,
shapes, and positions of the minerals that the
rock contains.
– Rock with large crystals or mineral grains has a
coarse-grained texture.
– Fine-grained texture describes rock with very small or
no visible crystals or mineral grains.
The Rock Cycle
• The rock cycle is the
continual process by which
new rock is formed from old
rock material. Each type of
rock can be changed into
every other type of rock.
Igneous Rock
• Igneous rock forms when hot, liquid
rock, or magma, cools and hardens.
• The type of igneous rock that forms
depends on:
1. composition of the magma and
2. the amount of time it takes the
magma to cool.
Igneous rock starts out
as magma.
Magma is created in three
ways:
1. when rock is heated,
2. when pressure is released,
3. when the composition of
the rock changes.
Melting
3 ways igneous rock can melt
into magma or be created:
• Pressure - The high pressure deep inside the
Earth forces minerals to stay in the solid state.
When hot rock rises to shallow depths, the
pressure is released and the rock can melt.
• Temperature - A rise in temperature can cause
the minerals in a rock to melt. Different melting
points cause some of the minerals to melt while
other minerals remain solid.
• Composition - When fluids such as water
combine with rock, the composition of the rock
changes, which lowers the melting point of the
rock enough for it to melt
Igneous rocks are formed when magma
cools.
• If the magma comes to the surface
of the Earth, it is called lava.
• Igneous rocks are formed when
some of the melted magma rises
to a higher level in the mantle of
the earth.
• The magma’s temperature lowers
(cools) and begins to solidify—
creating rock. This usually occurs
at the edges of tectonic plates.
• Igneous rocks also form
when parts of the Earth’s
crust cave in and melt.
• This melted crust returns to
the surface, cools and
solidifies.
• Granite and basalt are
common types of igneous
rocks.
Igneous rocks are broken
down into 2 types:
1 – intrusive
(plutonic)
2 – extrusive
(volcanic)
Intrusive Igneous rocks
• Intrusive rocks solidify within the crust of the
Earth and form great masses of regular
crystals.
• They are usually hidden because they are
formed under the crust.
• Uplift and erosion bring these rocks to the
Earth’s surface over time, and they become
exposed.
• When rocks solidify in cracks through which the
magma flows, it is called an igneous vein—and
both large and small crystals are formed.
• A geological process called uplift causes
areas of the Earth’s crust to rise to higher
elevations.
• That means, rocks deep inside the earth
can be moved to the surface by motions of
the Earth’s crust. When a rock reaches
the surface of the Earth, the processes of
weathering and erosion begin.
Extrusive igneous rocks
• Extrusive igneous rocks
solidify outside the crust,
after volcanic eruptions.
• They form with very few
crystals.
Magma can cool at different rates. The longer it takes for magma or
lava to cool, the more time crystals have to grow. The more time
crystals have to grow, that coarser the texture of the igneous rock.
Sedimentary
rocks are formed
when layers of
earth have been
deposited in the
bottoms of bodies
of water. Over
time these layers
are pressed
together forming
sedimentary rocks.
Erosion by wind and water
on the Earth’s surface
break down rocks into
small pieces called
sediments. These
sediments contain organic
(carbon based lifeform)
remains, and are moved by
the wind and water.
• In the areas where the
fragments are deposited, the
sediments cling together,
become compacted, and
undergo a CHEMICAL
CHANGE!
• This compaction and chemical
change is caused by great
pressure, which cements the
fragments together and forms
sedimentary rock.
• Limestone and shale are the most
common types of sedimentary rocks.
• Sedimentary rocks make up 75% of the
rocks on the Earth’s land surfaces.
• Sedimentary rocks are classified by their
grain size.
Metamorphic rocks were once
sedimentary or igneous rocks
that have been placed under
tons of pressure and heat.
Metamorphic rocks
• Metamorphic rocks have an extremely
varied composition. They are formed by
the transformation of igneous or
sedimentary rock.
• This change occurs when either igneous
or sedimentary rock masses are subjected
to conditions of high pressure and/or
temperature.
This causes the rock’s
structure to CHANGE
CHEMICALLY and creates
new minerals.
Textures of metamorphic rock
• All metamorphic rock has one of 2 textures:
foliated or non-foliated
• Foliation - Metamorphic rock that is foliated
contains minerals that are arranged in planes or
bands. Rocks that contain a variety of minerals
tend to form foliated rocks.
• Because minerals are aligned, foliated rocks
split into layers. Metamorphic rocks are often
classified by their texture (fine, medium or
coarse-grained).
Textures of
metamorphic
rock
Revisit the Rock Cycle
• Over time, all rock is broken down by the
forces of wind and water into sediments.
This action is called weathering.
Weathering
• Weathering and erosion are the cause of the
production and movement of sediments.
• There are 2 types of weathering:
– Mechanical – breaks the rocks apart physically
without changing the chemical composition of the
original rock. (Ex. Ice breaks a rock)
– Chemical – changes the chemical composition of the
rock (ex. Acid rain eroding rock).
• Rocks are
continuously
changing
from one
type to
another,
although very
slowly, and
this process
is called the
rock cycle.
• As you can see, all the different kinds of
rocks are being continuously recycled. No
matter how they are formed, eventually
they will be broken down by erosive
forces.
• Much of the sediments formed by the wind
and water erosion are deposited into the
sea, where new sedimentary rocks will be
formed.
• The grinding movement of the Earth’s
tectonic plates also recycles rocks. Pieces
of igneous and seabed sedimentary rock
get broken off and are added to the cycle.
• These fragments can be dragged
downward, where new metamorphic rocks
can be formed by heat and pressure.
• Then volcanoes can bring them back up to
the surface to form igneous rock and
eventually start the erosion process all over
again.
• This cycle has been going on for millions of
years.
A rock can be a thing
of beauty.