Op ch05 lecture_earth3, minerals

Chapter 5: Patterns in Nature: Minerals Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 5Patterns in Nature: Minerals

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

earthearth

LECTURE OUTLINE

Patterns in Nature: MineralsPatterns in Nature: Minerals

Prepared by

Ronald Parker Earlham College Department of Geosciences

Richmond, Indiana

Prepared by

Ronald Parker Earlham College Department of Geosciences

Richmond, Indiana


MineralsMinerals The “building blocks” of rocks, and hence, of The “building blocks” of rocks, and hence, of

Earth. Earth. More than 4,000 are known.More than 4,000 are known. Dozens of new minerals are discovered annually.Dozens of new minerals are discovered annually. Human interest in minerals spans millenia. Human interest in minerals spans millenia.


MineralsMinerals Developed societies depend on mineral resources.Developed societies depend on mineral resources.

Metals – Iron, copper, lead, zinc, nickel, aluminum, etc. Metals – Iron, copper, lead, zinc, nickel, aluminum, etc. Non-metals – Gypsum, limestone, aggregate, clay.Non-metals – Gypsum, limestone, aggregate, clay.


MineralsMinerals Economically important – Drive world economies.Economically important – Drive world economies. Historically important – Dictated human history.Historically important – Dictated human history.

Iron.Iron. Copper.Copper. Gold.Gold. Diamonds.Diamonds. Gems.Gems.


Mineral DefinitionMineral Definition Geologic definition of a mineral is specialized:Geologic definition of a mineral is specialized:

Naturally occurring.Naturally occurring. Solid.Solid. Formed geologically.Formed geologically. Definite chemical Definite chemical

composition. composition. Ordered atomic Ordered atomic

arrangement. arrangement. Mostly inorganic.Mostly inorganic.

Gypsum


RocksRocks Rocks are Earth materials made from minerals.Rocks are Earth materials made from minerals. Most rocks have more than one kind of mineral.Most rocks have more than one kind of mineral.

Example: GraniteExample: GranitePotassium feldspar.Potassium feldspar.Quartz.Quartz.Hornblende.Hornblende.

Some are monomineralic.Some are monomineralic. Limestone (Calcite).Limestone (Calcite). Rock salt (Halite).Rock salt (Halite). Glacial ice.Glacial ice.


Crystalline StructureCrystalline Structure Atoms in a mineral are specifically ordered.Atoms in a mineral are specifically ordered. A solid with disordered atoms is called a glass. A solid with disordered atoms is called a glass.

Crystalline structure based on atomic patterns. Crystalline structure based on atomic patterns.


CrystalsCrystals Rare minerals displaying flat external faces.Rare minerals displaying flat external faces. Crystal faces form best in open cavities.Crystal faces form best in open cavities.


CrystalsCrystals Constancy of interfacial angles.Constancy of interfacial angles.

The same mineral has the same crystal faces.The same mineral has the same crystal faces. Adjacent faces occur at a diagnostic angle. Adjacent faces occur at a diagnostic angle.

Faces and angles reflect the atomic arrangement. Faces and angles reflect the atomic arrangement.


Crystal LatticeCrystal Lattice Ordered atoms in crystals form a 3-D lattice. Ordered atoms in crystals form a 3-D lattice. Lattices are patterns that repeat in 3 dimensions. Lattices are patterns that repeat in 3 dimensions. This internal pattern controls mineral properties. This internal pattern controls mineral properties.

Crystal shape.Crystal shape. Symmetry. Symmetry.


Atomic BondingAtomic Bonding Lattice atoms are held in place by atomic bonds.Lattice atoms are held in place by atomic bonds. Bond characteristics govern mineral properties. Bond characteristics govern mineral properties. 5 recognized types of bonds.5 recognized types of bonds.

Covalent.Covalent. Ionic.Ionic. Metallic.Metallic. Van der Waals.Van der Waals. Hydrogen.Hydrogen.

Models depict atoms, bonds, and lattices.Models depict atoms, bonds, and lattices.


PolymorphsPolymorphs Same composition but different crystal structure.Same composition but different crystal structure. Polymorphs reveal the importance of bond type. Polymorphs reveal the importance of bond type. Diamond and graphite are carbon polymorphs (C). Diamond and graphite are carbon polymorphs (C).

Diamond – Strong covalent bonds; hardest mineral.Diamond – Strong covalent bonds; hardest mineral. Graphite – Weak Van der Waals bonds; softest mineral.Graphite – Weak Van der Waals bonds; softest mineral.

GraphiteGraphiteDiamondDiamond


Crystal GrowthCrystal Growth Crystals grow as atoms attach to mineral surfaces. Crystals grow as atoms attach to mineral surfaces. Growth starts from a central seed crystal.Growth starts from a central seed crystal. Growth expands outward as atoms accumulate.Growth expands outward as atoms accumulate.


Outward crystal growth fills available space.Outward crystal growth fills available space. Resulting crystal shape governed by surroundings.Resulting crystal shape governed by surroundings.

Open space – Good crystal faces grow.Open space – Good crystal faces grow. Confined space – No crystal faces. Confined space – No crystal faces.

Crystals grow by… Crystals grow by… Solidification from a melt.Solidification from a melt. Precipitation from solution.Precipitation from solution. Solid-state diffusion.Solid-state diffusion.

Crystal GrowthCrystal Growth


Atomic PackingAtomic Packing Ionic size (radius) and charge control packing. Ionic size (radius) and charge control packing.

Ion – Atom charged due to gain or loss of an electron.Ion – Atom charged due to gain or loss of an electron. Cation – Positive ion due to loss of electron(s).Cation – Positive ion due to loss of electron(s). Anion – Negative ion due to gain of electron(s).Anion – Negative ion due to gain of electron(s).

Ionic radii due to # of electrons; anions are bigger.Ionic radii due to # of electrons; anions are bigger.


Atomic PackingAtomic Packing Anions and cations bond to neutralize charges.Anions and cations bond to neutralize charges. Anion – Cation “fit” governed by relative size.Anion – Cation “fit” governed by relative size.

Large central cation – Larger number of anions.Large central cation – Larger number of anions. Small central cation – Smaller number of anions.Small central cation – Smaller number of anions.


Mineral Physical PropertiesMineral Physical Properties Characteristics determined by your 5 senses.Characteristics determined by your 5 senses. Used to ID minerals.Used to ID minerals. Properties depend upon…Properties depend upon…

Chemical composition.Chemical composition. Crystal structure.Crystal structure.

Some are diagnostic.Some are diagnostic.

Example: Pyrite (FeS2) Example: Pyrite (FeS2)

Cubic crystals, high specific gravity, striated crystal faces, black Cubic crystals, high specific gravity, striated crystal faces, black streak, metallic luster, dull brassy color, sulfur smell when streak, metallic luster, dull brassy color, sulfur smell when

crushed, crushed, erroneously mistaken for gold (fool’s gold).erroneously mistaken for gold (fool’s gold).

Minerals have a unique set of physical properties. Minerals have a unique set of physical properties.

PyritePyrite


Physical PropertiesPhysical Properties Common properties:Common properties:

Color.Color. Streak.Streak. Luster.Luster. Hardness.Hardness. Specific gravity.Specific gravity. Crystal habit.Crystal habit. Crystal form.Crystal form. Fracture.Fracture. Cleavage.Cleavage.

Needle-like crystal habit


ColorColor Color is diagnostic for some minerals.Color is diagnostic for some minerals.

Olivine is olive green.Olivine is olive green. Azurite is always blue.Azurite is always blue.

Some minerals may exhibit a broad color range.Some minerals may exhibit a broad color range. Quartz (Clear, white, yellow, pink, purple, gray, etc).Quartz (Clear, white, yellow, pink, purple, gray, etc).

Color varieties often reflect trace impurities. Color varieties often reflect trace impurities.

Quartz – Many colorsQuartz – Many colors Malachite – Always greenMalachite – Always green


StreakStreak Color of a mineral crushed on unglazed porcelain.Color of a mineral crushed on unglazed porcelain. Streak is often a useful diagnostic property.Streak is often a useful diagnostic property.

Congruent streak – Streak color same as mineral. Congruent streak – Streak color same as mineral. Magnetite – Black mineral; black streak.Magnetite – Black mineral; black streak.

Incongruent streak – Streak color different than mineral.Incongruent streak – Streak color different than mineral.Chromite – Black mineral; greenish-brown streak.Chromite – Black mineral; greenish-brown streak.

Hematite – Red-brown streakHematite – Red-brown streak


LusterLuster The way a mineral scatters light.The way a mineral scatters light. Two subdivisions. Two subdivisions.

Metallic – Looks like a metal.Metallic – Looks like a metal. Nonmetallic.Nonmetallic.

Vitreous (glassy).Vitreous (glassy).Satiny.Satiny.Silky.Silky.Resinous.Resinous.Pearly.Pearly.Earthy (dull). Earthy (dull). Adamantine (brilliant).Adamantine (brilliant).

Satin spar Gypsum – Satiny lusterSatin spar Gypsum – Satiny luster

Quartz – Vitreous lusterQuartz – Vitreous luster


HardnessHardness Scratching resistance of a mineral. Scratching resistance of a mineral. Hardness compared to the Mohs Hardness Scale.Hardness compared to the Mohs Hardness Scale.

1.1. Talc, GraphiteTalc, Graphite

2.2. GypsumGypsum

3.3. CalciteCalcite

4.4. FluoriteFluorite

5.5. ApatiteApatite

6.6. Orthoclase Orthoclase

7.7. QuartzQuartz

8.8. TopazTopaz

9.9. CorundumCorundum

10.10. DiamondDiamond

Glass - Steel 5.5

Fingernail 2.5

Copper Penny 3.5

Steel File 6.5


Crystal HabitCrystal Habit Crystal habit is the ideal shape of crystal faces.Crystal habit is the ideal shape of crystal faces. Ideal growth requires ideal conditions. Ideal growth requires ideal conditions. Many terms are used to describe habit. Many terms are used to describe habit.

Cubes Hexagonal PrismsBlades

RhombohedraDodecahedra

Octahedra

Tetragonal PrismsCompound Forms


Crystal FormCrystal Form Minerals vary in crystal face development.Minerals vary in crystal face development.

Euhedral – Good crystal faces; grown in open cavity.Euhedral – Good crystal faces; grown in open cavity. Anhedral – No crystal faces; grown in tight space. Anhedral – No crystal faces; grown in tight space. Subhedral – Between the two.Subhedral – Between the two.

Face development indicates growth history.Face development indicates growth history. Anhedral crystals common; euhedral less so. Anhedral crystals common; euhedral less so.

Amethyst GeodeAmethyst Geode


FractureFracture Some minerals lack planes of weakness. Some minerals lack planes of weakness. Due to equal molecular bonds in all directions.Due to equal molecular bonds in all directions. These minerals don’t have cleavage; they fracture.These minerals don’t have cleavage; they fracture.

Example: Quartz displays conchoidal fracture.Example: Quartz displays conchoidal fracture.Shaped like the inside of a clam shell. Shaped like the inside of a clam shell. Breaks along smooth curved surfaces.Breaks along smooth curved surfaces.Produces extremely sharp edges.Produces extremely sharp edges.

ObsidianObsidian


CleavageCleavage Tendency to break along planes of weakness. Tendency to break along planes of weakness. Cleavage produces flat, shiny surfaces.Cleavage produces flat, shiny surfaces. Described by number of planes and their angles.Described by number of planes and their angles. Sometimes mistaken for crystal habit. Sometimes mistaken for crystal habit.

Cleavage is through-going; often forms parallel “steps.”Cleavage is through-going; often forms parallel “steps.” Crystal habit is only on external surfaces. Crystal habit is only on external surfaces.

1, 2, 3, 4, and 6 cleavages possible. 1, 2, 3, 4, and 6 cleavages possible.


Cleavage Cleavage Examples of Cleavage:Examples of Cleavage:

1 direction1 direction

2 directions at 90º2 directions at 90º

2 directions NOT at 90º2 directions NOT at 90º

Muscovite MicaMuscovite Mica

AmphiboleAmphibole

Potassium FeldsparPotassium Feldspar


Cleavage Cleavage Examples of Cleavage:Examples of Cleavage:

3 directions at 90º3 directions at 90º

3 directions NOT at 90º3 directions NOT at 90º

CalciteCalcite

HaliteHalite


Mineral CompositionsMineral Compositions Only about 50 minerals are abundant. Only about 50 minerals are abundant. 98.5% of crustal mineral mass is from 8 elements.98.5% of crustal mineral mass is from 8 elements.

Oxygen Oxygen OO 46.6%46.6% SiliconSilicon SiSi 27.7%27.7% Aluminum Aluminum AlAl 8.1% 8.1% IronIron FeFe 5.0% 5.0% Calcium Calcium CaCa 3.6% 3.6% Sodium Sodium NaNa 2.8% 2.8% Potassium Potassium KK 2.6% 2.6% Magnesium Magnesium MgMg 2.1% 2.1% All others All others 1.5% 1.5%

74.3% of crustal minerals !!! 74.3% of crustal minerals !!!


Mineral ClassesMineral Classes Minerals are classified by their dominant anion.Minerals are classified by their dominant anion.

Silicates Silicates SiOSiO224- 4- Rock-forming minsRock-forming mins

OxidesOxides OO2-2- Magnetite, Magnetite, HematiteHematite

SulfidesSulfides SS-- Pyrite, GalenaPyrite, Galena SulfatesSulfates SOSO44

2-2- GypsumGypsum Halides Halides ClCl-- or F or F-- Fluorite, HaliteFluorite, Halite CarbonatesCarbonates COCO33

2-2- Calcite, DolomiteCalcite, Dolomite Native ElementsNative Elements Cu, Au, CCu, Au, C Copper, GraphiteCopper, GraphiteFluorite (Halide) Native CopperMalachite (Carbonate)


Silicates are know as the rock-forming minerals. Silicates are know as the rock-forming minerals. They dominate the Earth’s crust. They dominate the Earth’s crust.

Oxygen and silicon… Oxygen and silicon… Make up 94.7 % of crustal volume, and...Make up 94.7 % of crustal volume, and...74.3 % of crustal mass. 74.3 % of crustal mass.

Silicate MineralsSilicate Minerals


The anionic unit is the silica tetrahedron.The anionic unit is the silica tetrahedron. 4 oxygen atoms are bonded to 1 silicon atom (SiO4 oxygen atoms are bonded to 1 silicon atom (SiO44

4-4-).). Silicon is tiny; oxygen is huge. Silicon is tiny; oxygen is huge. The silica tetrahedron has a net -4 ionic charge.The silica tetrahedron has a net -4 ionic charge. The silicate unit can be depicted by…The silicate unit can be depicted by…

Spheres.Spheres.A ball and stick model.A ball and stick model.Polyhedra. Polyhedra.

Silicate MineralsSilicate Minerals


Silicate MineralsSilicate Minerals Silica tetrahedra link together by sharing oxygens.Silica tetrahedra link together by sharing oxygens. More shared oxygen = lower Si:O ratio; governs…More shared oxygen = lower Si:O ratio; governs…

Melting temperature.Melting temperature. Mineral structure and cations present. Mineral structure and cations present. Susceptibility to chemical weathering. Susceptibility to chemical weathering.

Type of Silicate Structure Formula Si:O Ratio

Independent TetrahedraIndependent Tetrahedra SiOSiO44 0.250.25

Double TetrahedraDouble Tetrahedra SiSi22OO77 0.290.29

Ring SilicatesRing Silicates SiSi66OO1818 0.330.33

Single ChainsSingle Chains SiOSiO33 0.330.33

Double ChainsDouble Chains SiSi44OO1111 0.360.36

Sheet SilicatesSheet Silicates SiSi22OO55 0.400.40

Framework SilicatesFramework Silicates SiOSiO22 0.500.50


Independent TetrahedraIndependent Tetrahedra Tetrahedra share no oxygens - linked by cations.Tetrahedra share no oxygens - linked by cations.

Olivine Group.Olivine Group.High temperature Fe-Mg silicate.High temperature Fe-Mg silicate.Small green crystals; no cleavage.Small green crystals; no cleavage.

Garnet Group.Garnet Group.Equant crystals with no cleavage.Equant crystals with no cleavage.Dodecahedral (12 sided) crystals.Dodecahedral (12 sided) crystals.

KyaniteKyaniteGarnetGarnet


Single-Chain SilicatesSingle-Chain Silicates Single-chain structures bonded with Fe and Mg.Single-chain structures bonded with Fe and Mg.

Pyroxene Group.Pyroxene Group.Black to green color. Black to green color. Two distinctive cleavages at nearly 90°.Two distinctive cleavages at nearly 90°.Stubby crystals.Stubby crystals.Augite is the most common pyroxene.Augite is the most common pyroxene.

PyroxenePyroxene


Double-Chain SilicatesDouble-Chain Silicates Double chain of silica tetrahedra bonded together. Double chain of silica tetrahedra bonded together. Contain a variety of cations.Contain a variety of cations.

Amphibole Group - Two perfect cleavages;Amphibole Group - Two perfect cleavages;

elongate crystals. elongate crystals.

HornblendeHornblende


Sheet SilicatesSheet Silicates 2-dimensional sheets of linked tetrahedra.2-dimensional sheets of linked tetrahedra. Characterized by one direction of perfect cleavage.Characterized by one direction of perfect cleavage.

Mica Group – Biotite (dark) and Mucsovite (light).Mica Group – Biotite (dark) and Mucsovite (light). Clay Mineral Group – Feldspar weathering residue; tiny. Clay Mineral Group – Feldspar weathering residue; tiny.

Muscovite Mica


Framework SilicatesFramework Silicates All 4 oxygens in the silica tetrahedra are shared.All 4 oxygens in the silica tetrahedra are shared.

Feldspar Group – Plagioclase and potassium feldspar.Feldspar Group – Plagioclase and potassium feldspar. Silica (Quartz) Group – Contains only Si and O. Silica (Quartz) Group – Contains only Si and O.

Potassium FeldsparPotassium Feldspar


DiamondsDiamonds Diamonds originate under extremely high pressure.Diamonds originate under extremely high pressure.

~ 150 km deep – in the upper mantle.~ 150 km deep – in the upper mantle. Pure carbon is compressed into the diamond structure.Pure carbon is compressed into the diamond structure.

Rifting causes deep mantle rock to move upward.Rifting causes deep mantle rock to move upward. Diamonds are found in kimberlite pipes.Diamonds are found in kimberlite pipes.


Chapter 5Patterns in Nature: Minerals

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

earthearth

LECTURE OUTLINE

This concludes the

Op ch05 lecture_earth3, minerals

Education

Transcript of Op ch05 lecture_earth3, minerals