Minerals of Earth’s
Crust
Chapter 3
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Mineral
• A naturally occurring, inorganic solid that
has a crystal structure and a definite
chemical composition.
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Mineral
• Must occur naturally
• Formed by processes in natural world
• Not manufactured (made by man)
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Mineral
• Must be inorganic
• Not made of living things or the remains of
living things
• Nonexample: coal
• Comes from the remains of plants and animals
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Mineral
• Must be a solid
• Definite (unchanging) shape and definite
volume
• Particles are tightly packed
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Mineral
• Must have a crystal structure
• Has flat sides that meet at sharp edges and
corners
• Atoms arranged in regular, repeating pattern
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Mineral
• Must have a definite chemical composition
• Always contains certain elements in the same
proportions
• Example: Quartz has one atom of silicon
for every two atoms of oxygen
• Pure, solid elements (mostly metals) are
also minerals
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Physical properties of minerals
• Result of chemical composition and
crystalline structure
• Useful for identifying minerals
• Many can be seen with the eye
• Others need tests and special equipment
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Color
• Easy to observe
• Not very useful
• Many have similar colors
• Small amounts of impurities can dramatically
change colors
• Ruby and sapphire are both types of corundum
• Weathered surfaces may hide color
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Streak
• Color of mineral in powdered form
• More reliable than just color
• Tested by rubbing across a streak plate of
unglazed ceramic tile
• Streak color may be different than mineral
color
• Even though the color of a mineral may vary,
its streak color is always the same
• Minerals that are harder than streak plate leave
no streak
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Luster
• Light that is reflected from a mineral’s surface
• Metallic – like polished metal
• Or nonmetallic
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Glassy
Waxy
Greasy
Pearly
Submetallic or dull
Silky
Earthy
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Discuss
• Define “mineral” in your own words.
• Amber is a precious material used in
jewelry. It forms when the resin of pine
trees hardens into stone. Is amber a
mineral? Explain.
• What does the phrase “definite chemical
composition” mean?
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Density
• The amount of mass in a given space
• Mass per unit volume
• You can compare the densities of two minerals by
lifting two samples that are the same size and
seeing which is heavier
• Calculate density by taking mass divided by
volume
• Depends on the kinds of atoms in a mineral and
how closely they are packed.
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Hardness
• Measure of the ability to resist scratching
• Determined by the strength of the bonds
between atoms
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Mohs Hardness Scale
• Standard scale for mineral hardness
• To test an unknown mineral you must
determine the hardest mineral on the scale it
can scratch.
• If neither of two minerals scratches the
other, they have the same hardness
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Crystal Structure
• Six basic shapes
• A certain mineral always has the same basic
shape
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Cleavage
• Tendency to split along specific planes of
weakness to form smooth, flat surfaces
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Fracture
• Tendency to break unevenly into pieces that
have curved or irregular surfaces
• Described by how it looks when it breaks
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Shell-shaped fracture
Hackly fracture (jagged points)
Earthy fracture (crumbly)
Uneven fracture (rough surface)
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Special properties
• Fluorescence – the ability to glow under
ultraviolet light
• Phosphorescence – the ability to keep
glowing after the ultraviolet light is turned
off
• Chemical reactivity
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Special properties
• Asterism – a six-sided star appears in
reflected light
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Special properties
• Double refraction
• Light bending through the mineral produces a
double image
• Magnetism
• Radioactivity
• Unstable
• Decay over time releasing particles and energy
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Discuss
• Name eight properties that are used to
identify minerals
• Compare and contrast fracture and
cleavage.
• Graphite is made of carbon atoms arranged
in thin sheets. The sheets are weakly held
together. Predict whether graphite will
break apart with fracture or cleavage.
Explain.
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Crystallization
• How atoms in a crystal structure get
arranged in that structure
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Minerals from magma and lava
• Magma – molten rock beneath Earth’s
surface
• Lava – what magma becomes when it
reaches the surface
• Both form crystals as they cool and solidify
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Cooling rates
• Magma far underground cools slowly
• Large crystals, especially if undisturbed
• Lava and magma close to the surface cool
more quickly
• Smaller crystals
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Minerals from solutions
• Solution – one substance dissolved in
another
• Minerals dissolved in water
• Crystallize when they leave the solution
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Evaporation
• Minerals formed at the edges of bodies of
water
• Minerals formed as ancient seas evaporated
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Geode
• Rounded hollow rock that is lined with
mineral crystals
• Formed when solutions of minerals seep
into the rock through a crack and then the
water evaporates
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Hot water solutions
• Hot water dissolves minerals
• The solution flows through cracks in other
rocks
• As the water cools, crystallization occurs
• A vein is formed
• Narrow channel or slab of a mineral that is
different from the surrounding rock
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Discuss
• What is crystallization?
• What factor affects the size of crystals that
form as magma cools?
• What is a solution?
• What are two ways in which minerals can
form from a solution?
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Gemstones
• Hard, colorful minerals with brilliant or
glassy luster
• Valuable minerals
• Once polished, called gems
• Used for decoration, mechanical parts,
grinding and polishing
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Metals
• Not as hard as gemstones
• Can be made into wires, thin sheets,
hammered, and molded without breaking
• Conduct heat and electricity well
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Other uses
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Medicines
Fertilizers
Talc – baby powder
Gypsum – sheetrock, cement, stucco
Calcite – optical instruments
Quartz – glass, watches, electronics
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Ore
• Rock containing minerals to be mined and
sold
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Producing metals from minerals
• Prospecting – searching for ore
• Can use magnetic field for iron, nickel, and cobalt
• Mining – getting ore out of ground
• Strip mines, pit mines, shaft mines
• Smelting – getting metals out of ore
• Use density differences to separate
• Additional processing
• Remove impurities
• Make alloys
• Solid mixtures of a metal and another element
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Discuss
• What are gemstones? Why are they
valuable?
• What is an ore?
• What properties of metal make them useful
to humans?
• If you were making a machine with lots of
small, moving parts that must run
constantly, would you make it out of metal
or gemstones? Explain.
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