Lecture Outlines

Physical Geology, 15/e

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Plummer, Carlson & Hammersley

Atoms, Elements, and Minerals

Physical Geology 15/e, Chapter 2

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Mineral – a naturally occurring, inorganic, crystallinesolid that has a specific chemical composition.

• forms in the geosphere, hydrosphere, biosphere, andeven the atmosphere

• consistent and recognizable physical and chemicalproperties

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Minerals and Rocks

Atoms – the smallest, electrically neutralassemblies of energy and matter

Central Nucleus

• protons (+ charged)

• neutrons (0 net charge)

Surrounding Cloud

• electrons (- charged)

Element – “Species of atom” defined by itsatomic number which is the number of protonsin its nucleus.

•92 naturally occurring elements

•Isotopes – varieties of an element that have differentnumbers of neutrons but the same number of protons.

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Atoms and Elements

Isotopes – atoms of an element with different

numbers of neutrons

• stable isotopes

o retain all of their protons and neutronsthrough time

o stable isotopes of oxygen can be used totrack climate change over time

• unstable or radioactive isotopes

o spontaneously lose proton(s) and/orneutron(s) from their nuclei over time

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Atoms and Elements

IONS AND BONDING

Ions – atoms or groups of atoms withunequal numbers of protons and electrons,thus having a non-zero charge

• positive and negative ions are attractedto one another and may stick orchemically bond together

Bonding – controlled by outermost shell(valence) electrons

• elements will typically be reactiveunless their valence shell is full

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Atoms and Elements

IONS AND BONDING

Ionic bonding – involves the transferof valence electrons from one atom toanother

Covalent bonding – involves sharingof valence electrons among adjacentatoms

Metallic bonding – electrons flowfreely throughout metals; results in highelectrical conductivity

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Atoms and Elements

Crystalline Structures• Atoms must be in close proximity to

each other for bonding to occur

• Opposite charges allow the ions to be“glued” in place as their charges areneutralized.

• Creates regular arrangements ofatoms in crystalline structures.

• The Silicate minerals are a veryimportant group of minerals formedfrom the two most common elementsin the crust – silicon and oxygen

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Atoms and Elements

The Silicon-Oxygen Tetrahedron• Strongly bonded silicate ion

• Basic structure for silicate minerals

• Isolated Silicate Structure

• Chain Silicates

• Sheet Silicates

• Framework Silicates

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Atoms and Elements

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Atoms and Elements

The Silicon-Oxygen Tetrahedron

• the more shared Oxygen atoms pertetrahedra, the more complex thesilicate structure

o isolated tetrahedra (none shared)

o chain silicates (2 shared)

o double-chain silicates (alternating 2and 3 shared)

o sheet silicates (3 shared)

o framework silicates (4 shared)

Non-Silicate minerals

• Carbonates – contains CO3 in their structures (calcite - CaCO3)

• Sulfates – contains SO4 in their structures (gypsum - CaSO4. 2H2O)

• Sulfides – contains S (but no O) in their structures (pyrite - FeS2)

• Oxides – contains O, but not bonded to Si, C or S (hematite - Fe2O3)

• Native elements – composed entirely of one element (diamond – C)

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Atoms and Elements

• Limited number of mineralcompositions and structures

• Solid solutions series - a rangeof compositions in commonsilicate minerals.Compositional zoning alsooccurs as in Fig. 2.15

• Polymorphism - when mineralswith the same compositionhave different crystallinestructures such as graphite anddiamond

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Variations inMineral Structures and Compositions

Rock-forming minerals

• > 4500 minerals identified

• > 90% of Earth’s crust is composed of minerals from only 5groups (feldspars, pyroxenes, amphiboles, micas, quartz)

Identification of Minerals - Requires the determination of thecharacteristic physical properties and matching them with amineral identification key

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The Physical Properties of Minerals

Color – visible hue of a mineral

Streak – color left behind when

mineral is scraped on unglazed porcelain

Physical and chemical properties of minerals are closely linked to their atomicstructures and compositions

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The Physical Properties of Minerals

Luster – manner in which light

reflects off surface of a mineral

Hardness – scratch-resistance

External Crystal form – external

geometric form

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The Physical Properties of Minerals

Cleavage – breakage along flat

planes

Fracture – irregular breakage

Specific gravity – density relative to that of water

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The Physical Properties of Minerals

ExcellentCleavage

ConchoidalFracture

Special Properties

• Striations –straight parallel lineson the flat surfaces of crystalfaces

• Magnetism – attracted to magnet

• Double Refraction – two imagesare visible when looking throughthe mineral

Chemical Tests – calciteeffervesces (bubbles) in diluteHCl

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The Physical Properties of Minerals

Precipitates – minerals that form from a crystallizing liquidsuch as silicates and carbonates

Biological Activity – mineral formed from the actions ofliving organisms such as coral reefs

Sublimation – minerals that form as gases from volcanicvents crystallize into solids such as sulfur

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The Many Conditions of Mineral Formation

End of Chapter 2

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