What is a Mineral?. What Exactly is a Mineral? Compositionally and physically distinct substance...
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Transcript of What is a Mineral?. What Exactly is a Mineral? Compositionally and physically distinct substance...
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What is a Mineral?
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What Exactly is a Mineral?
• Compositionally and physically distinct substance
• Four criteria to be a true mineral…
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Naturally Occurring Created through natural geologic processes
Synthetic diamond: not a mineral Raw diamond: mineral
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InorganicThat is, they do not consist of carbon-hydrogen molecules that may also form crystalline substances through biological processes
Sugar: It looks like a mineral, but is it?
Nope. Note the C-H bonds.
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SolidLiquid water Snowflake—frozen water
Not a mineral Mineral…believe it or not
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Definite Chemical CompositionMinerals are complex assemblages of multiple elements
Chemical Formula
Types of atoms involved and relative proportions
Ex. Quartz
Chemical formulaSiO2
Ex #2: Elbaite
Chemical formulaNa(Li,Al)3Al6(BO3)3Si6O18(OH)4
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Elements
• Pure chemical substance composed of one type of atom (i.e. specific # of protons…)
• 88 naturally occurring elements• Most common (i.e. compose 98% of the
earth’s crust—and therefore, minerals)– Oxygen, silicon, aluminum, iron, calcium,
magnesium, potassium, and sodium
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Atomic Structure
• Atom– Basic unit of an element– Very, very, very small
(1/10,000,000,000 m)– Nucleus
– Protons (+)– Neutrons (neutral)
– Electrons (-)– “cloud” surrounding
nucleus—exist in “shells”
– Mostly empty space
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Visualizing the size of an atom
• The nucleus is very small compared to the overall size of an atom
• Imagine 5 ½ football fields (minus end zones) placed end to end (100 yrds long x 160’ wide)
• Nucleus is like a grain of sand in the middle of them
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It’s All About the Electrons, Baby…
• A stable atom is one in which the outermost shell of electrons is completely filled
• Atoms can fill their outer shells by bonding to other atoms– Ionic bonding– Covalent bonding
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Bonding in a [Nut] Shell…
• Ionic Bonding– Cations (atoms that have
lost an electron) are attracted to anions (atoms that have gained an extra electron)
– Neutral compounds – Weaker but more
common than covalent bonds
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Bonding in a [Nut] Shell…
• Covalent bonding– Two or more atoms
share their electrons, producing the effect of filled outer electron shells
– Very strong bond
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Crystalline Structure• Arrangement of atoms
are– Orderly– Regular– 3-D– Repeating pattern
Halite
Biotite
Fluorite
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Can You Spot the Mineral Wannabes?
PyriteFeS2
oil
ChalcanthiteCuSO4-5H2O
Silicon CarbideSiC
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Growing a Mineral
• Unit cell—smallest unit structure of a mineral
• Brick Wall example
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Growing a Mineral: Halite
Halite unit cell
Halite crystal
What halite looks like to us
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Identifying a Mineral
• All minerals have physical and chemical properties that can be easily recognized
• Direct result of structure and composition
• Crystal habit• Cleavage• Fracture• Hardness• Color • Streak• Luster
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Cleavage
• Not the kind you’re thinking of…
• The tendency of a mineral to break along flat surfaces
• Governed by bond strength and crystal structure
• Stronger bonds = poor or no cleavage→
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Oooo…shiny!• Luster
– The way a mineral reflects light
• A metallic mineral is said to have a metallic luster
• Those that do not have a metallic luster (non-metallic) are assigned names that are self-explanatory – Pearly, resinous, earthy,
glassy, etc…
Pyrite has a metallic luster
Quartz has a glassy luster
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School of Hard Knocks…• Hardness
– Resistance of a mineral to scratching
• Hardness can be determined by scratching mineral with an object of known hardness
• Scale—Mohs– Based on 10 minerals: 1
being talc and 10 being diamond