Minerals and rocks
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Minerals and Rocks. Lecture Outline. What are minerals? Common rock-forming minerals Physical properties of minerals Basic rock types The rock cycle. Minerals. A mineral is a naturally occurring, solid crystalline substance, generally inorganic, with a specific chemical composition.

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Lecture outline
Lecture Outline

  • What are minerals?

  • Common rock-forming minerals

  • Physical properties of minerals

  • Basic rock types

  • The rock cycle


Minerals
Minerals

A mineral is a naturally occurring, solid

crystalline substance, generally inorganic,

with a specific chemical composition

  • Natural

  • Solid

  • Atoms arranged in orderly repeating 3D array: crystalline

  • Not part of the tissue of an organism

  • Composition fixed or varies within defined limits

    Minerals are the “building blocks” of rock


Minerals and rocks

Large individual crystals (rare)

Mass of small grains: each is a crystal, but grown up against each other


Atomic structure of minerals
Atomic Structure of Minerals

  • NaCl - sodium chloride

    Halite


Chemical bonds ionic
Chemical Bonds: Ionic

  • Electrical attraction between ions of opposite charge

    • Bond strength increases with the electrical charges of the ions

    • Bond strength decreases as the distance between the ions increases

  • Most minerals are this kind of compound


Minerals and rocks

Ionic Bonding example:

halite

Cation

Anion

Na+

Cl-


Covalent bonds
Covalent Bonds:

  • Electron sharing

  • Generally stronger than ionic bonds (e.g., diamond)


Crystallization of minerals
Crystallization of Minerals

  • Need starting material with atoms that can come together in the proper proportions

    • Growth from a liquid or a gas

  • Time and space for crystallization

  • Appropriate temperature and pressure

  • Examples

    • Magma that has cooled below its melting point

    • Supersaturated solution --> precipitation


Crystallization of minerals1
Crystallization of Minerals

  • Crystals begin as an initial “seed” - a microscopic crystal

  • Atoms keep being added in a 3D array, repeating the basic arrangement

  • Crystal faces are based on the array structure


Cations and anions
Cations and Anions

  • Anions are typically large

  • Cations are relatively small

  • Crystal structure is determined largely by the arrangement of the anions


Minerals and rocks

Common cations and anions

Radii given in angstroms; 10-8 cm


Ions can be compound
Ions can be compound

  • So far, we’ve talked about individual atomic ions

  • Many common minerals are silicates

SiO44-

Complex ions act as a single ion in forming crystal structure


Cation substitution
Cation Substitution

  • Crystal structure determined by those large anions

  • Various cations can substitute for each other in many minerals

    • Same crystal structure

    • Different chemical composition


Polymorphs
Polymorphs

Minerals with the same composition, but different crystal structure.


Minerals and rocks

Common Rock-Forming Minerals

Minerals fall into a small number of related “families” based mainly on the anion in them


Silicates
Silicates

  • Quartz (SiO2), K-feldspar (KAlSi3O8), olivine ((Mg, Fe)2SiO4), kaolinite (Al2Si2O5(OH)4)

  • Most abundant minerals in the Earth's crust

  • Silicate ion (tetrahedron), SiO44-



Silicate structure
Silicate structure

  • Most of the most common rocks in the crust are silicates

  • Silicate tetrahedra can combine in several ways to form many common minerals

  • Typical cations:

    K+, Ca+, Na+, Mg2+, Al3+, Fe2+



Carbonates
Carbonates

  • Cations with carbonate ion (CO32-)

  • Calcite (CaCO3), dolomite (CaMg(CO3)2), siderite (FeCO3), smithsonite (ZnCO3)

  • Make up many common rocks including limestone andmarble

  • Very important for CCS!



Minerals and rocks

CaCO3 + 2H+ = Ca2+ + CO2 + H2O



Oxides
Oxides

  • Compounds of metallic cations and oxygen

  • Important for many metal ores needed to make things (e.g., iron, chromium, titanium)

  • Ores are economically useful (i.e., possible to mine) mineral deposits



Sulfides
Sulfides

  • Metallic cations with sulfide (S2-) ion

  • Important for ores of copper, zinc, nickel, lead, iron

  • Pyrite (FeS2), galena (PbS)



Sulfates
Sulfates

  • Minerals with sulfate ion (SO42-)

  • Gypsum (CaSO4.H2O), anhydrite (CaSO4)



Minerals and rocks

Gypsum

  • Cave of the Crystals

  • 1,000 feet depth in the silver and lead Naica Mine

  • 150 degrees, with 100 % humidity

  • 4-ft diameter columns 50 ft length


Identification of minerals
Identification of Minerals

  • Chemical composition (microprobes and wet chemical methods)

  • Crystal structure (X-ray diffraction)

  • Physical properties



Physical properties1
Physical properties

  • Hardness

  • Cleavage: tendency of minerals to break along flat planar surfaces into geometries that are determined by their crystal structure





Physical properties2
Physical properties

  • Hardness

  • Cleavage

  • Fracture: tendency to break along other surfaces (not cleavage planes)



Physical properties3
Physical properties

  • Hardness

  • Cleavage

  • Fracture

  • Luster (metallic, vitreous, resinous, earthy, etc.)

  • Color (often a poor indicator; streak color is better)

  • Specific gravity

  • Crystal habit (shape)


Rocks
Rocks

An aggregate of one or more minerals; or a body of undifferentiated mineral matter (e.g., obsidian); or of solid organic matter (e.g., coal)

  • More than one crystal

  • Volcanic glass

  • Solidified organic matter

  • Appearance controlled by composition and size and arrangement of aggregate grains (texture)


Rock types
Rock Types

  • Igneous

    • Form by solidification of molten rock (magma)

  • Sedimentary

    • Form by lithification of sediment (sand, silt, clay, shells)

  • Metamorphic

    • Form by transformations of preexisting rocks (in the solid state)


  • Igneous rocks
    Igneous Rocks

    Intrusive

    Extrusive


    Intrusive plutonic
    Intrusive (plutonic)

    • Form within the Earth

    • Slow cooling

    • Interlocking large crystals

    • Example = granite


    Extrusive volcanic
    Extrusive (volcanic)

    • Form on the surface of the Earth as a result of volcanic eruption

    • Rapid cooling

    • Glassy and/or fine-grained texture

    • Example = basalt





    Origin of sediment
    Origin of sediment

    • Produced by weathering and erosion or by precipitation from solution

    • Weathering = chemical and mechanical breakdown of rocks

    • Erosion = processes that get the weathered material moving


    Sediment types
    Sediment types

    • Clastic sediments are derived from the physical deposition of particles produced by weathering and erosion of preexisting rock.

    • Chemical and biochemical sediments are precipitated from solution.


    Minerals and rocks

    Clastic

    Chemical/biochemical


    Lithification
    Lithification

    • The process that converts sediments into solid rock

    • Compaction

    • Cementation





    Minerals and rocks

    conglomerate

    metaconglomerate


    Minerals and rocks

    granite

    gneiss