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Earth Science Chapter 3 1
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
• 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• 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
• 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.