Mineral Identification

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Mineral Identification
Objective
3 Define chemical and physical properties of
minerals to include luster, hardness, cleavage,
fracture, streak, color, specific gravity, and
special traits.
Enduring Understanding
• Minerals are the building blocks of rocks.
Mineral Identification
• With more than 3,000 minerals in Earth’s crust
how does one go about identifying an
unknown mineral?
Mineral Identification
• Geologists rely on several simple tests that are
based on a mineral’s physical and chemical
properties. It is usually best to use a
combination of tests rather than just one to
identify minerals
Mineral Properties
• Color is one of the most noticeable but least
reliable characteristics
Mineral Properties
• Sometimes caused by the presence of trace
elements or compounds
Mineral Properties
• Streak is the color of the mineral when it is
broken up into a powder and is a much more
reliable identification method because it
rarely changes
Both of these samples are hematite; both have a reddish-brown streak
Mineral Properties
• Streak is easily determined by rubbing the
mineral across an unglazed porcelain plate
Mineral Properties
• Streak is used to distinguish pyrite from gold
Mineral Properties
• Streak is used to distinguish pyrite from gold
Mineral Properties
• Luster is the way a mineral reflects light from
its surface and is caused by differences in
mineral chemical compositions
Mineral Properties
• Either metallic or nonmetallic (dull, pearly,
waxy, silky)
Mineral Properties
• Texture describes how a mineral feels to the
touch
– Rough, smooth, ragged, greasy, soapy, glassy
Mineral Properties
• Hardness is a measure of how easily a mineral
can be scratched and is determined by the
arrangement of it’s atoms.
Mineral Properties
• The Mohs hardness scale is used to compare a
sample to the hardness of ten known minerals
Mineral Properties
• Cleavage determines whether a mineral will
split easily and evenly along one or more flat
planes
Mineral Properties
• Mica has perfect cleavage in one direction
• Halite has cubic cleavage (3 planes)
Mineral Properties
• Fracture means the mineral is tightly bonded
and breaks with rough or jagged edges
– Quartz has fracture
Mineral Properties
• Specific Gravity compares the weight of the
mineral to an equal volume of water at 4
degrees C
Mineral Properties
• Special Properties such as light reflection and
reactions to acids are also useful tools
Mineral Properties
• Calcite fizzles when in contact with HCl
Mineral Properties
• Calcite also can cause double images
Mineral Properties
• Magnetite will attract iron
Mineral Properties
• Sulfur produces a rotten egg odor
Minerals
•Minerals
have four characteristics
4
Naturally occurring—
formed by processes on or inside
Earth with no input from humans
Inorganic—
not made by life processes
Living
Element or compound with a
definite chemical composition
Orderly arrangement of atoms;
all minerals are crystalline solids
Crystal—solid with
atoms arranged in
orderly, repeating
patterns
Some crystals form from magma, hot
melted rock below the Earth’s surface.
When magma cools
slowly, crystals are
large.
When magma cools
quickly, crystals are
small.
Crystals can form from solutions as water
evaporates or if too much of a substance is
dissolved in water.
• Mineral groups are defined by their
composition.
• Silicates contain silicon, oxygen, and one
or more other elements; they include
most common rock-forming minerals.
• Silicon and oxygen are the two most
abundant elements in Earth’s crust; they
form the building blocks of many minerals.
DISCUSSION QUESTION:
• What processes can cause crystals to form?
DISCUSSION QUESTION:
• What processes can cause crystals to form?
Crystals form from cooling magma, from
evaporating solutions, and from solutions in
which too much of a substance is dissolved.
Mineral Identification
• Color and appearance are not enough to
distinguish most minerals.
• Hardness is a measure of how easily a
mineral can be scratched; the Moh’s scale
compares mineral hardness.
1.
2.
3.
4.
Talc - easily scratched by the fingernail
Gypsum - just scratched by the fingernail
Calcite - scratches and is scratched by a copper coin
Fluorite - not scratched by a copper coin and does not
scratch glass
5. Apatite - just scratches glass and is easily scratched by a
knife
6. Orthoclase - easily scratches glass and is just scratched by a
file
7. Quartz - (amethyst, citrine, tiger's-eye, aventurine) not
scratched by a file
8. Topaz - scratched only by corundum and diamond
9. Corundum - (sapphires and rubies) scratched only by a
diamond
10.Diamond - scratched only by another diamond
1 - Talc
2 - Gypsum
3 - Calcite
4 - Flourite
5 - Apatite
6 - Orthoclase
7 - Quartz
8 - Topaz
9 - Corundum
10 - Diamond
• The way a mineral reflects light is its luster.
• Luster can be metallic or nonmetallic
• Nonmetallic lusters include dull, pearly, silky, and
glassy.
Specific gravity is the relationship between
a mineral’s density to the density of
water. If the specific gravity is larger than
one it will sink in water, if it is smaller
than one it will float in water.
Streak is the color of a mineral in powdered
form, but the streak test is useful only for
minerals softer than the streak plate.
The way a mineral breaks can be a
distinguishing characteristic.
Minerals with
cleavage break
along smooth,
flat surfaces.
Minerals with fracture break with uneven,
rough, or jagged surfaces.
Some minerals have unique properties that
involve light or magnetism.
DISCUSSION QUESTION:
• What are five properties that could be
examined to identify a mineral?
DISCUSSION QUESTION:
• What are five properties that could be
examined to identify a mineral?
hardness, luster, specific gravity, streak,
cleavage, and fracture
Gems—rare and beautiful minerals that are highly prized
The Cullinan diamond
and the Hope diamond
are famous historical gems.
Gems have industrial
applications in abrasives,
lasers, and electronics.
Minerals can contain other useful elements.
An ore is a mineral or rock containing a
substance that can be mined at a profit.
Elements must be refined, or purified, from
ores.
• Some elements dissolve in fluids, travel through
weaknesses in rocks, and in those weaknesses
form mineral deposits called vein mineral
deposits.
Titanium is a useful element
derived from the minerals
ilmenite and rutile.
Mica is an example of a mineral with the
characteristic of cleavage,
because it can
be separated into sheets.
Graphite is one of the softest
minerals and is used in pencils.
Sulfur is a bright yellow mineral with
distinctive odor of spoiled eggs.
the
Calcite is a hard carbonate mineral
Feldspar is the most abundant
mineral in the Earth's crust
Hematite is an iron based mineral,
colored black, silver-gray, reddish
brown, or red.
Halite – the mineral sodium chloride
also known as table salt
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