Patterns in Nature: Minerals -...

2005 Earlham Physical Geology Geosciences 211Lecture 5: Minerals

© 2005, Ronald L. ParkerThursday, January 27, 2005

Essentials of Geology, 2004, by Stephen MarshakW. W. Norton & CompanyChapter 3: Patterns in Nature: Minerals 1

Patterns in Nature: MineralsPatterns in Nature: Minerals

January 27, 2005January 27, 2005

© 2003, R

on Parker©

2003, Ron Parker Geosciences 211, Physical Geology © 2005, Ron ParkerGeosciences 211, Physical Geology © 2005, Ron Parker Geosciences 211, Physical Geology © 2005, Ron Parker

Minerals Make up the lithosphere, mantle and the core.

The “building blocks” of rocks.

Over 4000 are known.

Developed societies depend on mineral resources. Metals – Iron, copper, lead, zinc, nickel, aluminum, etc. Non-metals – Gypsum, limestone, aggregate, clay.

Preserve information about conditions of formation.

Make up the lithosphere, mantle and the core.

The “building blocks” of rocks.

Over 4000 are known.

Developed societies depend on mineral resources. Metals – Iron, copper, lead, zinc, nickel, aluminum, etc. Non-metals – Gypsum, limestone, aggregate, clay.

Preserve information about conditions of formation.

Geosciences 211, Physical Geology © 2005, Ron Parker

Mineral Definition Definition of a mineral:

Homogenous (uniform throughout)

Naturally occurring (no synthetics)

Inorganic (no biological)

Solid (no liquids or gases)

Ordered internal molecular structure Definite chemical composition

A solid that exhibits some (but not all) of these properties is a mineraloid.


Rocks Rocks are earth materials made from minerals. Most rocks have more than one mineral.

Example: Granite Potassium feldspar Quartz Hornblende

Some rocks are monomineralic. Limestone (Calcite) Rock salt (Halite) Glacial Ice ©

2003, Ron Parker

© 2003, R

on Parker


Crystalline Structure Disordered atomic arrangement (glass).

Ordered atomic arrangement (mineral).

© W. W. Norton© W. W. Norton Geosciences 211, Physical Geology © 2005, Ron Parker

A mineral with crystal faces. Faces grow in open spaces. Faces reflect atomic order. Constancy of interfacial angles.

Crystals of the same mineral have the same crystal faces.

The angle between adjacent crystal faces is always the same.

CrystalsQuartz crystal © Jay SchomerQuartz crystal © Jay Schomer





Crystal Lattice The ordered 3-D atomic arrangement (crystal lattice) in minerals

reflects a repeating pattern. This internal pattern results in crystal symmetry.


Crystal Lattice The crystal lattice in minerals is revealed by X-Ray Diffraction

(XRD). Measuring lattice spacing by XRD permits mineral identification.

New Earlham Geology X-Ray DiffractometerNew Earlham Geology X-Ray Diffractometer

© 2003, R

on Parker©

2003, Ron Parker

© W. W. Norton© W. W. Norton


Minerals with The same chemical composition But different crystalline structures

Diamond and graphite are polymorphs (C).

Polymorphs

© W. W. Norton© W. W. Norton Geosciences 211, Physical Geology © 2005, Ron Parker

Crystal Growth Crystals grow by

Solidification from a melt. Precipitation from solution. Solid-state diffusion.

Minerals grow from a central seed

to fill the available space.

Mineral shape is controlled by

the shape of the surroundings.

Play Animation

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

Minerals grow from a central seed

to fill the available space.

Mineral shape is controlled by

the shape of the surroundings.

Play Animation

by Stephen Marshak

©, 2002, DIGIT, Prentice-Hall Geosciences 211, Physical Geology © 2005, Ron Parker

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

Chemical Composition Crystal Structure

Pyrite (FeS2) Cubic crystals, high specific gravity, striated crystal faces, black streak, metallic luster, dull brasscolor, sulfur smell, gold to fools





Physical PropertiesPhysical Properties Crystal Form Crystal Habit Luster Color Streak Hardness Cleavage Fracture Specific Gravity

Crystal Form Crystal Habit Luster Color Streak Hardness Cleavage Fracture Specific Gravity

Other Properties Taste Smell Effervescence Magnetism Feel Diaphaneity Piezoelectricity Pyroelectricity Refractive Index Elasticity Malleability Ductility SectilityBeryl var. aquamarineBeryl var. aquamarine


Crystal Form Ideal shape of crystal faces. Growth requires ideal conditions.

W. W. NortonW. W. Norton

Cubes Hexagonal PrismsBlades

RhombohedraDodecahedra

Octahedra

Tetragonal PrismsCompound Forms


Crystal Form Minerals may exhibit a range of crystal face

development. Euhedral – Well-developed crystal faces. Anhedral – No visible crystal faces. Usually

from growth in a confined space. Subhedral – Between the two.

Euhedral crystals - Growth in an open cavity.

Anhedral crystals - Growth in tight spaces.

Anhedral crystals common; euhedral rare.

Crystal QuartzCrystal Quartz

OlivineOlivine

Gold NuggetGold NuggetGeosciences 211, Physical Geology © 2005, Ron Parker

Appearance of reflected light Two basic categories

Metallic Nonmetallic

Vitreous (glassy) Silky Resinous Earthy (dull) Adamantine (brilliant)

Luster Topaz - vitreous

Vanadinite

Adamantine


Color Often unreliable for mineral ID. May vary due to impurity elements. Many gemstones are brightly colored.

Often unreliable for mineral ID. May vary due to impurity elements. Many gemstones are brightly colored.

Quartz (SiO2)Quartz (SiO2)

Exhibits a variety of colorsExhibits a variety of colors

©, 2002, DIGIT, Prentice-Hall©, 2002, DIGIT, Prentice-Hall

Emerald (Beryl)Emerald (Beryl)


Color of a mineral when scratched (crushed) on an unglazed porcelain plate.

Streak

Hematite – red-brown streakHematite – red-brown streakSphalerite – yellow streakSphalerite – yellow streak

Pyrite – black streakPyrite – black streak





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

1. Talc, Graphite2. Gypsum3. Calcite4. Fluorite5. Apatite6. Orthoclase 7. Quartz8. Topaz9. Corundum10. Diamond

Hardness

Fingernail 2.5

Copper Penny 3.5

Glass - Steel 5.5


Tendency to break along planes of lattice weakness. Cleavage produces flat, shiny surfaces. Described by resulting geometric shapes.

Number of planes Angles between adjacent planes

Discriminate from crystal form (which cleavage may resemble).

Cleavage


1 direction

2 directions at 90º

2 directions NOT at 90º

Cleavage

AmphiboleAmphibole

Potassium FeldsparPotassium Feldspar

Muscovite micaMuscovite mica


3 directions at 90º

3 directions NOT at 90º

Cleavage

CalciteCalcite

GalenaGalena


Cleavage 4 directions

6 directions

FluoriteFluorite

SphaleriteSphaleriteGeosciences 211, Physical Geology © 2005, Ron Parker

Conchoidal FractureConchoidal Fracture Some minerals lack planes of weakness = no cleavage. Due to equal molecular bonds in all directions. These minerals don’t cleave; they fracture.

Example: Conchoidal fracture Breaks in smooth curved surfaces. Very sharp edges. Shaped like the inside of a clam shell.

Conchoidal fracture in Quartz





Specific Gravity Ratio of the weight of a mineral to the weight of an

equal volume of water Average crustal value is 2.7 (quartz) Average mantle value is 3.3 (olivine)

SG is reflected in “heft” – how heavy the mineral feels. Galena – Heavy Feldspar - Light


Mineral Groups More than 4000 minerals have been identified. Only about 50 minerals are abundant. 98% of all minerals are made of 8 elements.

Oxygen O 46.6% Silicon Si 27.7% Aluminum Al 8.1% Iron Fe 5.0% Calcium Ca 3.6% Sodium Na 2.8% Potassium K 2.6% Magnesium Mg 2.1% All others 1.7%

Vanadinite

74.3 % of all minerals !!!74.3 % of all minerals !!!


Mineral Groups Minerals are classified based upon the dominant anion.

Silicates SiO24- Rock forming minerals

Carbonates CO32- Calcite, Dolomite

Sulfides S- Pyrite, Galena Oxides O2- Magnetite, hematite Sulfates SO4

2- Gypsum Halides Cl- or F- Fluorite, Halite


Dominate the Earth’s crust. Oxygen and silicon account for 74.3 % of crustal mass. Silicates are know as “the rock-forming minerals.”

Basic unit is the silica tetrahedron 4 oxygens bond to a much smaller silicon

Dominate the Earth’s crust. Oxygen and silicon account for 74.3 % of crustal mass. Silicates are know as “the rock-forming minerals.”

Basic unit is the silica tetrahedron 4 oxygens bond to a much smaller silicon

Silicate Minerals


Silicon to oxygen ratio (Si:O) controls properties. Low Si:O (Upper Mantle, Oceanic Crust)

Fe and Mg rich minerals. Higher…

Density Specific Gravity Temperature and Pressure

High Si:O (Continental Crust) Na and K rich minerals. Lower…


Silicon to oxygen ratio (Si:O) controls properties. Low Si:O (Upper Mantle, Oceanic Crust)

Fe and Mg rich minerals. Higher…


High Si:O (Continental Crust) Na and K rich minerals. Lower…


Silicate Minerals

Example: SerpentineExample: Serpentine

Example: QuartzExample: Quartz


Silicate Minerals

SiO2 0.50Framework Silicates

Si2O5 0.40Sheet Silicates

Si4O11 0.36Double Chain Silicates

SiO3 0.33Single Chain Silicates

SiO4 0.25Isolated Tetrahedra

Si:O RatioType of structure





Silica tetrahedra are linked together to form… Isolated Tetrahedra Double Tetrahedra Rings Single Chains Double Chains Sheets 3-D Frameworks

Silica tetrahedra are linked together to form… Isolated Tetrahedra Double Tetrahedra Rings Single Chains Double Chains Sheets 3-D Frameworks

Silicate Structures


Individual tetrahedra linked by cations Olivine Group

Hi T Fe-Mg silicate. Small crystals; no cleavage. Always olive green.

Garnet Group Small, rounded crystals with no cleavage. Dodecahedral crystals

Individual tetrahedra linked by cations Olivine Group

Hi T Fe-Mg silicate. Small crystals; no cleavage. Always olive green.

Garnet Group Small, rounded crystals with no cleavage. Dodecahedral crystals

Isolated Tetrahedra


Pyroxene Group Single chain structures with Fe and Mg. Black to green color. Two distinctive cleavages at nearly 90 degrees. Stubby crystals. Augite is the most common pyroxene.

Single Chain Silicates


Amphibole Group Double chain structures made of a variety of ions. Two perfect cleavages at 124 and 56 degrees. Elongate “bladed” crystals. Hornblende, the most

common amphibole, is black.

Amphibole Group Double chain structures made of a variety of ions. Two perfect cleavages at 124 and 56 degrees. Elongate “bladed” crystals. Hornblende, the most

common amphibole, is black.

Double Chain Silicates


Mica Group Sheet structures that result in one

direction of perfect cleavage Biotite is the common dark

colored mica mineral Muscovite is the common light

colored mica mineral Clay Mineral Group

Residue left from the weathering of feldspars.

Sheet Silicates


Feldspar Group The most common mineral group. 2 directions of perfect cleavage at 90°. 2 Major types

Potassium feldspar Plagioclase feldspar

Silica (Quartz) Group Second most common

Framework Silicates





Several major groups exist including Oxides Sulfides Sulfates Native Elements Carbonates Halides Phosphates

Non-silicate MineralsNext Class:Next Class:

Igneous Rocks

Reading: Marshak, 2004, Interlude A (pp. 98-104) and Chapter 3 )pp. 105-122)Jargon Quiz: Website

Reminder: Next Thursday (2/3) First Exam

Igneous Rocks

Reading: Marshak, 2004, Interlude A (pp. 98-104) and Chapter 3 )pp. 105-122)Jargon Quiz: Website

Reminder: Next Thursday (2/3) First Exam

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