Minerals and rocks

Click to edit Master text stylesSecond level Third level Fourth level Fifth level Large individual crystals rare Mass of small grains: each is a crystal, but grown up against each other.

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Minerals and Rocks

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Lecture Outline

 What are minerals?

 Common rock-forming minerals

 Physical properties of minerals

 Basic rock types

 The rock cycle

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Minerals

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

A mineral is a naturally occurring, solid crystalline substance, generally inorganic, with a specific chemical composition

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Large individual crystals (rare)

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

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Atomic Structure of Minerals

NaCl - sodium chloride

Halite

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Chemical Bonds: Ionic

 Electrical attraction between ions of opposite charge

 Bond strength increases with the electrical charges of

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Na+

Cl-Ionic Bonding example: halite

Anion Cation

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Covalent Bonds:

Electron sharing

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

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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

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Cations and Anions

 Anions are typically large

 Cations are relatively small

 Crystal structure is

determined largely by the

arrangement of the anions

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Second level

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Fifth levelCommon cations and anions

Radii given in angstroms; 10-8 cm

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Ions can be compound

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

 Many common minerals are silicates

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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

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Minerals with the same composition, but different crystal structure.

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Common Rock-Forming Minerals

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

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Most abundant minerals in the Earth's crust

Silicate ion (tetrahedron),

SiO44- Quartz (SiO2), K-feldspar (KAlSi3O8), olivine ((Mg, Fe)2SiO4), kaolinite (Al2Si2O5(OH)4)

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Second level

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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+

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Different numbers of oxygen ions are shared among tetrahedra

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 Cations with carbonate ion (CO32-)

 Calcite (CaCO3), dolomite (CaMg(CO3)2), siderite

(FeCO3), smithsonite (ZnCO3)

 Make up many common rocks including limestone and

marble

 Very important for CCS!

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 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

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 Metallic cations with sulfide (S2-) ion

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

 Pyrite (FeS2), galena (PbS)

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Second level

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 Minerals with sulfate ion (SO42-)

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

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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

Gypsum

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Physical properties

 Hardness

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 Hardness

 Cleavage: tendency of minerals to break along flat

planar surfaces into geometries that are determined

by their crystal structure

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Second level

Third level

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Fifth levelCleavage in mica

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Halite (NaCl)

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 Hardness

 Cleavage

 Fracture: tendency to break along other surfaces

(not cleavage planes)

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 Hardness

 Cleavage

 Fracture

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

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

 Specific gravity

 Crystal habit (shape)

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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)

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Igneous Rocks

Intrusive

Extrusive

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Basalt: igneous extrusive

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Second level

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Sedimentary Rocks

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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

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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

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Chemical/biochemical

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 The process that converts sediments into solid rock

 Compaction

 Cementation

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Metamorphic Rocks

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Second level

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Fifth levelconglomerate

metaconglomerate

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Second level

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gneiss

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The Rock

Cycle

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The Rock Cycle

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