Identify a mineral

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



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


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Large individual crystals (rare)

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


Atomic Structure of Minerals



NaCl - sodium chloride

Halite


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

Ionic Bonding example:
halite

Cation

Na

+

Anion

Cl

-


Covalent Bonds:


Electron sharing



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


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

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Examples



Magma that has cooled below its melting point

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Supersaturated solution --> precipitation


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


Anions are typically large



Cations are relatively small



Crystal structure is determined largely by the
arrangement of the anions


Common cations and anions
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Radii given in angstroms; 10

-8

cm


Ions can be compound


So far, we’ve talked about individual atomic ions



Many common minerals are silicates

4SiO4
Complex ions act as a single
ion in forming crystal structure


Cation Substitution



Crystal structure determined by those large anions

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Various cations can substitute for each other in many minerals

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Same crystal structure

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Different chemical composition


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Polymorphs


Minerals with the same composition, but different crystal structure.


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

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Silicates


Most abundant minerals in the Earth's crust



4Silicate ion (tetrahedron), SiO4

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


Quartz (SiO2)
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Silicate structure


Most of the most common rocks in the crust are silicates

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

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Typical cations:

+
+
+
2+ 3+
2+
K , Ca , Na , Mg , Al , Fe


Different numbers of oxygen ions are shared among tetrahedra


Carbonates



2Cations with carbonate ion (CO3 )



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



Make up many common rocks including limestone and marble

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Very important for CCS!


Calcite (CaCO3)

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+
2+
CaCO3 + 2H = Ca + CO2 + H2O

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Smithsonite (ZnCO3)