Transcript Text Book Pages - Atlanta Public Schools

Text Book Pages :
44 - 53
So what is a mineral?
A naturally occurring, inorganic solid that has
a crystal structure and a definite chemical
composition.
What are the characteristics of all minerals?
Now I See Crystal Clear!
► Naturally
Occurring
► Inorganic (Was Never
Alive)
► Solid
► Crystal Structure
► Chemical Composition
Naturally Occurring
Must be formed by processes in the
natural world.
Mineral Quartz forms naturally as molten
material cools and hardens deep beneath
Earth’s surface.
Are man made materials like
Plastic, brick, glass, and steel can be
called minerals?
Remember:
A mineral can not form from
organic materials (living things).
Is coal a mineral?
No, it comes from the remains of
plants that lived millions of
years ago.
►Has
definite volume and shape
►A
solid in which the atoms are arranged in a
pattern that repeats again and again.
► Has flat sides, called faces, that meets at sharp
edges and corners.
► Like
a snowflake pattern or rock candy.
Always contains
certain element in
definite proportions.
►
►Quartz
has one atom
of silicon for every two
atoms of oxygen.
Remember!:
Rarely is a mineral identified by a
single property.
These properties need to be
considered together to correctly
identify a mineral.
Of the almost 4000 known minerals,
only about 30 are common.
The most common are:
quartz, feldspar, mica, and calcite.
Fact:
Over 60% of the Earth’s crust is
made up of the family of minerals
known as feldspar!
Discuss the following!
There are four common minerals,
how many can you name?
Of the four common minerals,
which one makes up over 60% of
the Earth’s crust?
To be able to identify these and
other minerals, we need to look at
the properties used to separate
and distinguish these minerals.
Color is the most easily observed
mineral property and the least
useful!
Mineral azurite is always blue.
Mineral malachite is always green.
Many minerals have a similar
color.
Caution:
Many minerals have colors due to
impurities, or they can change
colors in various circumstances.
For example, pure quartz is
colorless or white, impurities can
make the mineral rose, purple or
pink!
Discuss the following!
How many of the characteristics
of minerals can you name?
Why isn’t color a very good
property to identify most
minerals?
Streak of a mineral is the color of its
powder when rubbed on an
unglazed white (porcelain) tile.
The streak is often not the same
color as the mineral.
A mineral’s color may vary, but the
streak rarely will!
Mineral sulfur has yellow
color,
but produces streak of white
color on black tile.
For example, Calcite occurs in many
different colors, shapes, and
varieties. But every single variety
of Calcite has a white streak. A
streak is useful in distinguishing
two minerals with the same color
but different streak.
► Minerals,
which streak very light colors, can
be easily identified on black streak plate.
►The
way a mineral reflects
light from its surface.
Notice the difference between these
two minerals?
The mineral on the left has a
metallic luster, the one on the
right, a nonmetallic luster.
Glassy luster
Pearly luster
Silky luster
Other terms that might be used include
greasy, dull, and earthy.
Can you tell which of these has an
earthy luster and which has a vitreous
luster?
Vitreous
Earthy
The hardness of a mineral is it’s
resistance to being scratched.
Diamond is the hardest of all minerals,
and talc is the softest.
Friedrich Mohs devised a hardness
scale.
In this scale, ten well known minerals
are given numbers from one to ten.
Lets take a look at the ten minerals
used and some of the simple tests.
Talc is the softest
and has a
hardness of 1.
A soft pencil lead
will scratch talc.
Gypsum is a bit
harder and has a
hardness of 2.
A fingernail
scratches gypsum.
Calcite has a
hardness of 3.
A copper penny
just scratches it.
Fluorite has a
hardness of 4.
It can be scratched
by an iron or brass
nail.
Apatite has a hardness
of 5.
It can be scratched by
a steel knife blade.
Feldspar has a
hardness of 6.
It will scratch a
window glass.
Quartz, with a
hardness of 7, is the
hardest of the
common minerals.
It easily scratches
hard glass and steel.
Topaz has a
hardness of 8.
It will scratch
quartz.
Corundum (left) has
a hardness of 9.
Diamond with its
hardness of 10.
Corundum will
scratch topaz.
It can easily scratch
the rest of the
minerals.
►The
cleavage of a mineral is it’s
ability to split easily along flat
surfaces.
Cleavage can even be observed on tiny
mineral grains making it a very useful
property!
Mica is probably the best example as
it splits into thin sheets. It is said
to have one perfect cleavage.
Feldspar splits readily in two
directions, always at or near right
angles.
Calcite and galena cleave in three
directions.
They are said to have three good cleavages.
►Not
all minerals show cleavage.
►Those that don’t break along
cleavage surfaces are said to have
fracture.
►Minerals break in irregular way.
Discuss the following!
Does this mineral show cleavage or
fracture?
Of the four most common minerals,
►which has the highest hardness?
►Which has the lowest hardness?
►Crystal
shape can be a useful
property to identify minerals if the
minerals have had the time and space
to form crystals.
 Most mineral grains that are found in
rocks, lack the room to grow.
►Specific
gravity tells you how many
times as dense as water the mineral
is.
►Pure gold can have a specific gravity
as high as 19.3!
►Calcite
►If
is calcium carbonate, CaCO3.
a drop of weak hydrochloric acid is
placed on calcite, the acid bubbles as
carbon dioxide is released.
Magnetic
Malleable
Radioactive
Flourescence
Taste
Minerals that can be hammered thin
or shaped are said to show these
properties.
Can you think of a mineral that
might be shaped or hammered?
Gold would be a perfect example!
Some minerals
that contain
Iron, are
magnetic and
can be picked up
by a magnet.
This is the state of
glowing while
under a ultraviolet
light.
Some minerals even
glow once the light
is turned off!
Some minerals, such
as this uraninite,
are radioactive.
They give off
subatomic particles
that will activate a
Geiger counter.
Halite (rock salt)
can be identified
by its taste.
This practice is not
recommended!