The document discusses minerals and rocks. It defines minerals as naturally occurring solids with a crystalline structure and specific chemical composition, while rocks are aggregates of minerals. There are over 4000 known minerals that are divided into classes based on their dominant chemical component, most importantly the silicates. Silicates are made of silica tetrahedra that bond together in different ways to form distinct mineral groups with varying properties. The document outlines several important physical properties used to identify minerals such as color, crystal structure, hardness, and cleavage.

1. Minerals and Rocks
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2. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
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3. Minerals
• The “building blocks” of rocks, and hence, of Earth.
• -more than 4000 are known
• -dozens of new minerals are discovered annually
•
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4. Minerals
• Societies depend on mineral resources.
• Metals: iron, copper, lead, zinc, nickel, aluminum, etc.
• Non-metals: gypsum, limestone, clay
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5. Minerals
• Economically important – Drive world economies.
• Historically important – Dictated human history.
• Iron.
• Copper.
• Gold.
• Diamonds.
• Gems.
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6. Mineral Definition
• Geologic definition of a mineral is specific.
• A naturally occuring solid, formed geologically, that has
a crystal structure and a specific chemical composition,
and is usually inorganic
• -doesn’t include “minerals in nutritional sense
• -A mineraloid exhibits some, but not all, properties
Gypsum
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7. Rocks
• Rocks are Earth materials made from minerals.
• Most rocks have more than one kind of mineral.
• -example: granite
• -mineral(s)?
• Potassium, quartz, hornblende
• -some are mono-mineralic
• Limestone (calcite), rock salt
• (halite), glacial ice
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8. Rock Definition
• Geologists definition: coherent, naturally occuring solid
made up of an aggregate of minerals (or more
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9. 3 Main Rock Types
1. Igneous – solidified from molten rock or melt
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10. 3 Main Rock Types
2. Sedimentary
3. -cemented/precipitated from rock fragments/solution
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11. 3 Main Rock Types
3. Metamorphic – existing rock altered by changes in
pressure and temperature
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12. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
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13. Crystalline Structure
• A solid with disordered atoms is called a glass
Glass
• Atoms in a mineral are specifically ordered
• Crystalline structure based on atomic patterns
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14. Crystals
• Minerals displaying flat external faces (rare).
• -crystal faces form best in open cavities
• -crystals are often prized mineral specimens
Beryl Quartz
Green, gem version -> emerald
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15. Crystals
• Constancy of angles between crystal faces.
• -same mineral always (ideal) has same crystal faces
• -adjacent faces occur at regular (diagnostic) angle
• Faces and angles reflect the atomic arrangement.
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16. Crystal Lattice
• Ordered atoms in crystals form a lattice.
• Lattices are patterns that repeat in 3D
• This internal pattern controls mineral properties.
• -crystal shape
• -planes of symmetry
•
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17. Determining Atom Arrangements
• X-Ray Diffraction (XRD) probes crystal lattices.
• Unique lattice spacing is used to ID minerals.
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18. Bonding of Atoms
• Lattice atoms are held in place by atomic bonds.
 Bond characteristics govern mineral properties.
• 5 recognized types of bonds (Appendix A).
• -covalent (gain/loose )
• -metallic
• -van
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19. Polymorphs (many + form)
• Same composition but different crystal structure.
• Polymorphs show the importance of bond type.
• Diamond and graphite are carbon polymorphs (C)
• -diamond: strong covalent bonds; hardest mineral
• -graphite: weak van der waals bonds; softest mineral
Diamond
Graphite
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20. Crystal Growth
• Crystals grow as atoms attach to mineral surfaces
• -growth starts from a central seed crystal
• -growth expands outward
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21. Crystal Growth
• Outward crystal growth fills available space.
• Resulting crystal shape governed by surroundings.
• -open space: good crystal faces grow
• -confined space: no crystal spaces
• Crystals mostly grow by…
• Solidification from a melt
• Precipitation from solution
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22. Atomic Packing
• Ion size (radius) and charge control packing.
• Ion – atom charged due to gain or loss of an electron
• Cation – positive ion due to loss of electron
• Anion – negative ion due to gain of electron
• Ionic radii due to # of electrons; anions are bigger.
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23. Atomic Packing
• Anions and cations bond to neutralize charges.
• Anion – Cation “fit” governed by relative size.
• -large central cation – larger number of anions
• -smalll central cation – smaller number of anions
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24. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
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25. Physical Properties of Minerals
• Characteristics determined by your senses.
• Used to ID minerals.
• Properties depend upon…
• -chemical composition
• -crystal structure
Some are diagnostic.
i.e. pyrite (fes2) Pyrite
-minerals have a unique
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26. Physical Properties
• Common properties:
• Color.
• Streak.
• Luster.
• Hardness.
• Specific gravity.
• Crystal habit (ideal shape).
• Crystal form.
• Fracture.
• Cleavage.
Needle-like crystal habit
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27. Physical Properties
• Less common physical properties:
• Taste. Magnetite crystals on a large magnet.
• Smell.
• Feel.
• Magnetism.
• Effervescence.
• Refractive index.
• Malleability.
Calcite effervesces with acid
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28. Color
• Color is diagnostic for some minerals.
• E.g. olivine/malachite is always green, azurite is always
blue
Some minerals may exhibit a broad color range.
-quartz (clear, white, yellow, pink, purple
Quartz – Many colors Malachite – always green
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29. Streak
• Color of a mineral struck across unglazed porcelain.
• Streak is often a useful diagnostic property.
• Congruent streak –streak color same as mineral
• -magnetite: black mineral; black streak
Incongruent streak – streak color different than mineral
-chromite: black mineral; greenish-brown streak
Hematite – Red-brown streak
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30. Luster
• The way a mineral scatters light.
• Two subdivisions.
• Metallic – Looks like a metal.
• Nonmetallic.
• Vitreous (glassy).
• Satiny.
• Silky.
• Resinous.
• Pearly. Quartz – Vitreous luster
• Earthy (dull).
• Adamantine (brilliant).
Satin spar Gypsum – Satiny luster
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31. Hardness
• Scratching resistance of a mineral.
• Hardness compared to Mohs Hardness Scale.
1. Talc, Graphite
2. Gypsum
Fingernail 2.5
3. Calcite
Copper Penny 3.5
4. Fluorite
5. Apatite
Glass - Steel 5.5
6. Orthoclase
Steel File 6.5
7. Quartz
8. Topaz
9. Corundum
10. Diamond
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32. Specific Gravity
• Related to density (mass per volume).
• Mineral weight over weight of equal water volume.
• Specific gravity is heft – how heavy it feels
• -pyrite: heavy (sg 5.0)
• -feldspar: light (sg 2.6)
• -pyrite feels heavier
Pyrite Potassium Feldspar
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33. Crystal Habit
• Crystal habit is the ideal shape of crystal faces.
• -ideal growth requires ideal conditions
• -many terms are used to describe habit
Cubes Octahedra Blades Hexagonal Prisms
Dodecahedra Rhombohedra Tetragonal Prisms
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34. Crystal Form
• Minerals vary in crystal face development.
• Euhedral – good crystal faces; gown in open cavity
• Anhedral – no crystal faces; grown in tight space
• Subhedral – between the two
• Face development indicates growth history
• Anhedral crystals common; euhedral less so.
Amethyst Geode
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35. Fracture
• Some minerals lack planes of weakness.
• Due to equal molecular bonds in all directions.
• These minerals fracture and hence don’t have cleavage.
• Example: Quartz
Obsidian
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36. Cleavage
• Tendency to break along planes of weakness.
• Due to equal molecular bonds in all directions.
• These minerals fracture and hence don’t have
cleavage.
• i.e. quartz displays conchoidal fracture
• -shaped like inside of a clam shell
• -breaks along smooth curved surfaces
• -cleavage produces flat surfaces
• -described by number of planes and their angles
• Sometimes mistaken for crystal habit. Chapter 5

37. Cleavage
• Examples of Cleavage:
Muscovite Mica
• 1 direction
• 2 directions at 90º
Potassium Feldspar
• 2 directions NOT at 90º
Amphibole
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38. Outline
• Minerals and rocks
-What are minerals? Geologic definition, significance.
-What are rocks? Geologic definition, 3 main types.
• Mineral structure
-Crystalline structure, crystals, crystal lattice
-Determining atom arrangement (XRD), atomic bonding
-Polymorphs, crystal growth and packing of atoms
• Physical properties of minerals
-Overview: common ones, less common ones
-Color, streak, luster, hardness, specific gravity, crystal habit/form,
fracture, and cleavage
• Mineral classes and silicates
-Mineral classes, most importantly silicates
-Silica tetrahedra building block
-Silicate types: from individual tetrahedra to framework Chapter 5 5
Chapter

39. Mineral Classes
• Minerals are classified by their dominant anion.
Silicates SiO24- Most rock-forming mins!
• Oxides O2- Magnetite, Hematite
• Sulfides S- Pyrite, Galena
• Sulfates SO42- Gypsum
• Halides Cl- or F- Fluorite, Halite
• Carbonates CO32- Calcite, Dolomite
• Native Elements Cu, Au, C Copper, Gold, Graphite
Malachite (Carbonate) Fluorite (Halide) Native Copper
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40. Silicate Minerals
• Silicates are known as the rock-forming minerals.
• They dominate the Earth’s crust.
• Oxygen and silicon…
• -94.7% of crustal volume
• -74.3% of crustal mass
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41. Silicate Minerals
• The building block (anion) unit is the silica tetrahedron.
• 4 oxygen atoms are bonded to 1 silicon atom (SiO44-).
• -silicon is tiny; oxygen is huge
• -the silica tetrahedron has a net -4 ionic charge
• -the silicate unit can be depicted by…
• -spheres
• -ball and stick model
• -polyhedra
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42. Silicate Minerals
• Silica tetrahedra link together by sharing oxygens.
• More shared oxygen  higher Si:O ratio; governs…
• -melting temp
• -mineral structure and cations present
• -susceptibility to chemical weathering
Type of Silicate Structure Formula Si:O Ratio
Independent Tetrahedra SiO4 0.25
Double Tetrahedra Si2O7 0.29
Ring Silicates Si6O18 0.33
Single Chains SiO3 0.33
Double Chains Si4O11 0.36
Sheet Silicates Si2O5 0.40
Framework Silicates SiO2 0.50
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43. Independent Tetrahedra
• Tetrahedra share no oxygens - linked by cations.
• Olivine Group.
• High temperature Fe-Mg silicate.
• Small green crystals; no cleavage.
• Garnet Group.
• Equant crystals with no cleavage.
• Dodecahedral (12 sided) crystals.
Garnet
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44. Single-Chain Silicates
• Single-chain structures bonded with Fe and Mg.
• Pyroxene Group.
• Black to green color.
• Two distinctive cleavages at nearly 90°.
• Stubby crystals.
• Augite is the most common pyroxene.
Pyroxene
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45. Double-Chain Silicates
• Double chain of silica tetrahedra bonded together.
• Contain a variety of cations.
• Amphiboles – two perfect cleavages
• Elongate crystals
Hornblende
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46. Sheet Silicates
• 2-dimensional sheets of linked tetrahedra.
• Characterized by one direction of perfect cleavage.
• Mica Group – botite (dark) and mucsovite (light)
Clay Mineral Group – feldspar weathering residue; tiny
Muscovite (Mica)
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47. Framework Silicates
• All 4 oxygens in the silica tetrahedra are shared.
• Feldspar Group – plagioclase and potassium feldspar
• Silica (Quartz) Group – contains only si and o
Potassium Feldspar
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