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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
2.7 What are the most important minerals?
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
2.7 What are the most important minerals?
• 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
2.7 What are the most important minerals?
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
How do minerals form?(crystallization)
Grow from solids (metamorphism)
analogy: ceramic firing in a kiln
How do minerals form?(crystallization)
Grow from gassesanalogy: ice crystals on a windshield; snowflakes
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