Earth Science Chapter 31 Minerals of Earth’s Crust Chapter 3

Earth Science Chapter 3 1

Minerals of Earth’s Crust

Chapter 3


Mineral• A naturally occurring, inorganic solid that

has a crystal structure and a definite chemical composition.


Mineral• Must occur naturally

• Formed by processes in natural world• Not manufactured (made by man)


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


Mineral• Must be a solid

• Definite (unchanging) shape and definite volume

• Particles are tightly packed


Mineral• Must have a crystal structure

• Has flat sides that meet at sharp edges and corners

• Atoms arranged in regular, repeating pattern


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


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


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


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


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


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?


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.


Hardness

• Measure of the ability to resist scratching• Determined by the strength of the bonds

between atoms


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


Crystal Structure

• Six basic shapes• A certain mineral always has the same basic

shape


Cleavage

• Tendency to split along specific planes of weakness to form smooth, flat surfaces


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)


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


Special properties• Asterism – a six-sided star appears in

reflected light


Special properties

• Double refraction• Light bending through the mineral produces a

double image

• Magnetism• Radioactivity

• Unstable• Decay over time releasing particles and energy


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.


Crystallization

• How atoms in a crystal structure get arranged in that structure


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


Cooling rates

• Magma far underground cools slowly• Large crystals, especially if undisturbed

• Lava and magma close to the surface cool more quickly• Smaller crystals


Minerals from solutions

• Solution – one substance dissolved in another• Minerals dissolved in water• Crystallize when they leave the solution


Evaporation

• Minerals formed at the edges of bodies of water

• Minerals formed as ancient seas evaporated


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


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


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?


Gemstones

• Hard, colorful minerals with brilliant or glassy luster

• Valuable minerals• Once polished, called gems• Used for decoration, mechanical parts,

grinding and polishing


Metals

• Not as hard as gemstones• Can be made into wires, thin sheets,

hammered, and molded without breaking• Conduct heat and electricity well


Other uses

• Medicines• Fertilizers• Talc – baby powder• Gypsum – sheetrock, cement, stucco• Calcite – optical instruments• Quartz – glass, watches, electronics


Ore

• Rock containing minerals to be mined and sold


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


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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Earth Science Chapter 31 Minerals of Earth’s Crust Chapter 3