Download File - Mrs. Ellis` Science Class!

To be able to identify these and other
minerals, we need to look at the
properties used to separate and
distinguish these minerals.
Remember!:
Rarely is a mineral identified by a
single property.
These properties need to be
considered together to correctly
identify a mineral.
Color is the most easily observed
mineral property and the least
useful!
Some exceptions to the color rule
would be cinnabar, which is always
red, and malachite, which is green.
Many minerals have a similar color.
Many minerals can turn 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?
Luster refers to the way a mineral
shines in reflected light.
Notice the difference between these
two minerals?
The mineral on the left has a
metallic luster, the one on the
right, a nonmetallic luster.
There are several terms used to describe
nonmetallic luster. Examples could be
vitreous, like the quartz on the left, or
pearly, like the gypsum on the right.
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
Streak of a mineral is the color of its
powder when rubbed on an unglazed
white tile.
The streak is often not the same color
as the mineral.
A minerals color may vary, but the
streak rarely will!
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.
Crystal Shape (or form)
• External expression of a mineral’s internal
atomic structure
• Planar surfaces called crystal faces
• Angles between crystal faces are constant for
any particular mineral
Quartz
Pyrite
The cleavage of a mineral is its tendency to
split easily or to separate along flat surfaces.
Cleavage can even be observed on tiny mineral
grains making it a very useful property!
Do NOT confuse cleavage planes with crystal
faces! Crystal faces are just on the surface
and may not repeat when the mineral is
broken!
Mica is probably the best example as it
splits into thin sheets. It is said to have
one perfect cleavage.
•
Cleavage (1 direction):
Example: mica
Feldspar splits readily in two directions,
always at or near right angles.
•
Cleavage (2 directions):
orthoclase
amphibole
Calcite and galena cleave in three directions.
They are said to have three good cleavages.
•
Cleavage (3 directions):
halite
calcite
•
Cleavage (4 directions):
fluorite
Not all minerals show cleavage.
Those that don’t break along cleavage
surfaces are said to have fracture.
Minerals that have some weak bonds will
show cleavage
Minerals,like quartz, that have very strong
bonds show fracture
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?
The hardness of a mineral is its
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
wellknown minerals are
given numbers from
one to ten.
Lets take a look at the ten
minerals used and some
of the simple tests.
Talc (left) 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 (left) has a hardness of 3 and a
copper penny just scratches it.
Fluorite has a hardness of 4 and it can be
scratched by an iron or brass nail.
Apatite (left) has a hardness of 5 and can
be scratched by a steel knife blade.
Feldspar has a hardness of 6 and it will
scratch a window glass.
Quartz (left), 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 and will scratch
quartz.
Corundum (left) has a hardness of 9.
Corundum will scratch topaz.
Diamond with its hardness of 10 can easily
scratch the rest of the minerals.
Discuss the following!
Does this mineral show cleavage or
fracture?
Of the four most common minerals,
which is the highest hardness?
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 is calcium carbonate, CaCO3. If 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!
Chemistry and Mineral PropertiesHardness
• The stronger the
bond, the Harder the
mineral
• Covalent bonds are
the usually the
hardest minerals; van
der Waals are the
softest minerals
• 3D structures are
harder than 2D
structures
• Minerals with water in
their structure are
generally softer
• Larger the cation &
anion Longer the bond,
the softer the mineral
Chemistry and Mineral PropertiesDensity
• The harder the mineral, the more dense
it usually is
Chemistry and Mineral PropertiesColor
• The most common cause of color in minerals
is interaction with light outer-shell electrons.
• Minerals of Hard cations (no outer shell
electrons) have no color and are white or
clear
• Minerals of Soft cations (a few outer-shell
electrons) commonly have colors unique to
the cation. (Hematite: Fe+3 is red)
Color of Minerals
USES OF MINERALS
2.9 Million Pounds!
►Lead: 777 lbs
►Iron: 14, 530 lbs
►Zinc: 544 lbs
►Clays: 12,121 lbs
►Copper: 932 lbs
►Salt: 31,779 lbs
►Aluminum: 4,040 lbs
►Stone, sand, & gravel:
1.11 million lbs
Common uses include:
•
•
•
•
•
•
Aluminum--packaging, transport, building
Beryllium--gemstones, fluorescent lights
Copper--electric cables, wires, switches
Feldspar--glass and ceramics
Iron--buildings, automobiles, magnets
Calcite--toothpaste, construction
• http://www.mii.org/commonminerals.php
Birthstones
►January: Garnet
►February: Amethyst
►March: Aquamarine
►April: Diamond
►May: Emerald
►June: Pearl &
Alexandrite
►July: Ruby
►August: Peridot
►September: Saphhire
►October: Tourmaline &
Opal
►November: Topaz and
Citrine
►December: Tanzanite,
Zircon, & Turquoise
Fireworks
Americans use 30,000 tons of fireworks per year! Lets look at
the minerals that make up the colors of fireworks
►Red: Strontrium
►Orange: mixture of
Strontrium and Sodium
►Yellow: sodium
►Gold sparks: iron fillings
and charcoal
►Bright Flashes:
Aluminum Powder
►Green: Barium
►Blues: Copper
►Lavender: mixture of
copper and strontium
►Silver/White: mixture of
titanium, zirconium, and
magnesium
►Silver/white flashes:
Magnalium
Time for some research!
►For homework, you will be doing the Mineral
Mania Project
►Use the following websites to get the
information not covered in class:
– http://www.minsocam.org/MSA/K12/uses/uses.h
tml for minerals in the home
– http://www.rocksandminerals.com/uses.htm for
uses of common minerals
►Ask me if you need print outs of the website!