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Minerals,Continued

Minerals

Crystalline Solidscrystalline = orderly arrangement of atoms

Naturally OccurringInorganic SubstancesDefinite Chemical Composition

eg: SiO2 for Quartz

“Atomic Mass Number”= # of protons + # of neutrons

“Atomic Number”

= # of protons

“Isotopes” are varieties of an element with

varying # of neutrons

Atomic structure

http://www.dayah.com/periodic/

http://periodic.lanl.gov/default.htm

Box 02.02.f1 Fig. 02.02

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Fig. 02.18

Bonds

Ionic -- exchange of electron(s)

Covalent – sharing electron(s)

Metallic – electrons move freely

Crystalline arrangement of Silicate Minerals all contain the Silicon-Oxygen Tetrahedron

Fig. 02.08

<= Single tetrahedrons require more positively charged ions

to maintain electrical neutrality…

<= …than two tetrahedrons sharing an oxygen atom

Diagramatic representation

Chemical Groupings of Minerals

Native elements --copperOxides --Corundum Al2O3

Sulfides –chalcopyrite, galena, pyriteHalides –Fluorite CaF2 Halite NaCl

Sulfates, Nitrates, Phosphates –gypsum, niter (KNO3 ), apatite

Carbonates --aragoniteSilicates

Ferromagnesian silicates (olivine)Felsic silicates (muscovite, quartz)

Fig. 02.08

<= Single tetrahedrons require more positively charged ions

to maintain electrical neutrality…

<= …than two tetrahedrons sharing an oxygen atom

Diagramatic representation

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Fig. 02.11

Single chain silicate structure

Fig. 02.09

The Physical Properties of Minerals

ColorStreakLusterHardnessExternal Crystal FormCleavage

Fig. 02.07

The Physical Properties of Minerals (cont.)

FractureSpecific GravitySpecial PropertiesChemical Tests

2.1 What are the properties of minerals? Color

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• Very small differences in composition, yet very large differences in color

Color 2.6 What determines the physical properties of minerals?

• Size and charge of ions matter– Smaller ions can fit

into tighter spaces– Often a structure will

prefer certain positive ions based on both charge and size

Fig 2.22

2.6 What determines the physical properties of minerals?

Fe3+

Ti4+

Fe2+

Mn2+

Fig 2.7

2.6 What determines the physical properties of minerals?

Crystal faces coincide with sloping planes of carbon atoms

Same composition – different structure

One is all covalent, one has van der Waals bondsBlack/gray

Opaque

1 cleavage

Hardness: 2

SG: 2.23

Electrical conductor

Various colors

Transparent

4 cleavages

Hardness: 10

SG: 3.51

Electrical insulator

Fig 2.23

Streak Luster

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Hardness

2.1 What are the properties of minerals?

Mohs hardness scale. Note the log scale of absolute hardness (Y axis).

Fig 2.4

• Fingernail (hardness ~2.5) scratches gypsum (hd ~2) External Crystal Form

quartz

fluorite

garnet

Cleavage

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Fig. 02.22

hornblende

Chrysotile asbestos

Fracture

• Lack of cleavage– irregular– chonchoidal

Conchoidalfracture

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SpecialProperties

• Striations• Magnetism• Taste• Double refraction

Striations on plagioclase

2.4 How do elements combine to form minerals?

• Water is a common covalent molecule– Here we see water

dissolving the ionic mineral NaCl (salt)

– In doing this it breaks the ionic bonds

Fig 2.16

2.4 How do elements combine to form minerals?

• Internal structure of minerals– Minerals often contain multiple bond types– Calcite for instance

– C and O in the carbonate group form a covalent ion

– Ca and carbonate bond ionically Fig 2.17

Calcite is ionicallysoluble in water (giving Ca2+/CO3

2– in solution)

But acid will break the covalent carbonate down and release CO2

Fig 2.18

Chemical Tests

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2.4 How do elements combine to form minerals?• Quartz too has both ionic and covalent bonds

– The SiO44– (silica group) is covalently bound

– Adjacent silica groups ionically bond to Si– The end result of quartz is SiO2 in a framework web.

Fig 2.19

2.7 What are the most important minerals?• Silicates

2.7 What are the most important minerals?• Silicates – contain SiO4

4– (silicate group)– Feldspars, the most common crustal mineral

• Al/Si substitution (aluminosilicates)• Na+, K+, Ca2+ are all found in feldspars

Large size difference –little substitution, K-spar contains little Na

NaNa++ and Caand Ca2+2+ close in size. With some Al/Si juggling we find a range of Na/Ca content in plagioclase feldspars.

Fig 2.25

2.7 What are the most important minerals?

• Three of the most common Fe/Mg containing silicates– Similar to plagioclase, Fe2+/Mg2+ are found in varying

amounts in these minerals– Each one represents a group of minerals (olivines)

Fig 2.26


Another common silicate

Garnets: a good example of ion substitutionHere we see how the various amounts of Fe, Mg, Mn, Cr, and Al affects the color range of garnet

Fig 2.27


• Nonsilicates– Carbonates: aragonite, dolomite– Oxides: metal ores, e.g., Fe3O4 – magnetite– Halite: NaCl (and some other halogen salts)– Sulfides: FeS – pyrite; PbS – galena– native elements: gold, silver, sulfur, copper

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2.7 What are the most important minerals?• Some important nonsilicates

Fig 2.28Fig 2.29

Fig 2.30

2.7 What are the most important minerals?• Nonsilicates


Minerals are important if they are common, useful, or both.

4,000 known but only a few dozen important rock-forming minerals, mostly from the top 10–12

elements.

Silicates are the most abundant mineral group.

Elements with similar ionic size and/or charge can substitute in some minerals.

Most economically valuable ores are nonsilicates, often oxides or sulfides

How do minerals form?(crystallization)

Grow from liquidsfrom water solutionsfrom melts


Grow from solids (metamorphism)

analogy: ceramic firing in a kiln


Grow from gassesanalogy: ice crystals on a windshield; snowflakes

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