Minerals

1
Minerals

• A. Changing scales to looking at the
• elements of the earth and its crust (8
  most common)
• B. Introduction to minerals that comprise rocks
• (11 most common minerals)
• C. The silicate minerals (7)
• D. Other important rock-forming minerals (4)
• E. Mineral properties

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A. Changing Scale Zooming in from global view to
atomic scale
The crust is made of rocks gt Rocks are made of
minerals gt
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Rocks ?Minerals?Atoms
Fig. 2.7

• Fig. 2.1
• Fig. 2.3
• Fig. 2.15
• Fig. 2.17a
• Fig. 2.19

Biotite
Quartz
Feldspar
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The Elements of the Crust and Where
They are Found

• O and Si make up most of the earths crust
  (including oceanic)
• O, Si, Al, Na and K are more abundant in the
  Continental Crust
• Fe, Mg, and Ca are much more abundant in the
  Oceanic Crust
• Fe and Mg make up more than half of the Mantle

Crustal
Crustal
Change in crust due to differentiation
Whole Earth (proto-earth) Percentage
?
30 15 lt1 35 lt1 lt1 lt1 10 8
Incr. ? Incr. ? Incr. ? Dcr. ? Incr. ? Incr.
? Incr. ? Dcr. ?
?
?
?
?

• O and Si make up most of the earths crust
  (including oceanic)
• O, Si, Al, Na and K are more abundant in the
  Continental Crust
• Fe, Mg, and Ca are much more abundant in the
  Oceanic Crust
• Fe and Mg make up more than half of the Mantle

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Atoms and Elements

• Nucleus
• Protons
• Charge
• Has Mass, Atomic
• Neutrons
• 0 Charge
• Mass similar to One Proton
• Atomic Mass
• Electrons
• In shells (2, 8, 8)
• - charge (balances each proton )
• Very little Mass

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Ions and Bonding

• Incomplete electron shells tend to be filled
• E.g. Chlorine (Cl-)
• 17 protons (at. 17)
• 17 electrons would make it neutral (no charge)
  with the last shell one electron short 2, 8, 7
  Soooo

• Tends to grab an electron to fill the third shell
• Making it a negatively charged Ion (anion)

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Ions and Bonding (cont.)

• Other Common Examples
• Sodium, at. 11 2, 8, 1 ? Na
• Oxygen, at. 8 2,6, ? O-2
• Silicon, at. 14 2,8,4 ? Si4

(Cation)
Fig. 2.5
Fig. 2.3 Oxygen (O-2)
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B. Introduction to Minerals

• Halite
• Mineral mined for rock salt and table salt
• Na gives electron to Cl
• Opposites attract, elements bond
• NaCl (Sodium Chloride)

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Intro to Minerals

• Fig. 2.18
• Fig. 2.20

• Repeating 3-D pattern forms a Crystalline Solid
  (or Crystal)
• Naturally occurring crystals are Minerals
• Crystalline structure and bonding leads to
  physical properties hardness, crystal form,
  cleavage? specific gravity (density)

Crystal Form? (Habit)
3 planes of cleavage
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Some Familiar Crystal Forms

• Quartz Crystal
• (SiO2)
• Snow Flake (Ice Crystal) due to crystalline
  structure of H2O

Fig. 2.15a
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Definition Mineral

• a. Crystalline solid
• b. Naturally Occurring
• (not artificial)
• c. Definite chemical
• composition
• some unique
• Many with a definite range of composition
  (mineral groups)

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C. Silicate Minerals

• Silica The chemical compound of Silicon and
  Oxygen
• Oxygen and Silicon are the most abundant elements
  in the earths crust, thus
• Silicate Minerals are a class of minerals that
  comprise most (gt90) of the crust
• Continental Crust is higher in silica
• Oceanic Crust is lower in silica

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Silica Tetrahedra and Silicate Minerals

• One Si and Four O s bond in a tetrahedron shape
• The silica tetrahedron is the basic building
  block of most minerals of the crust
• Silica tetrahedra bond with other tetrahedra by
  sharing Oxygens
• Other cations bond to form a wide variety of
  Silicate Minerals

SiO3-2

• Fig. 2.7
• Fig. 2.8
• Fig. 2.11

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Silicate Minerals (cont.)

• E.g., Olivine
• Isolated silicate structure
• Bonded with iron and magnesium
• Makes up much of the mantle
• Fe/Mg rich gt50 27
• Silica poor lt45 17

• Fe2(SiO4) to Mg2(SiO4)
• Ferromagnesian Mineral

27 Numbers in Square Brackets are atomic
ratios. E.g. 2 atoms Fe to total number of atoms
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Silicate Minerals (cont.)

• E.g., Pyroxene (Group of minerals)
• Single Chain Silicate structure
• bonded with Fe, Mg, Ca, and Al
• Found in Oceanic Crust
• Fe/Mg/Ca rich 15
• Silica poor 15
• X SiO3 X Fe2,Mg2, Ca2, and Al
• Also a Ferromagnesian Mineral
• 
  

SiO3-2
Cleavage and Form Prismatic
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Silicate MineralsOther Important examples
Silicate Structure
Example
Isolated Silicate Structure
Olivine

• Olivine most of mantle
• Pyroxene Oceanic Crust
• Amphibole Continental Crust
• Micas Biotite, Muscovite continental crust
• Clay In many soils
• Na and K Feldspar Continental Crust
• Ca Feldspar Oceanic Crust
• Quartz Continental Crust and many soils

Single Chain Structure
Pyroxene Group
Amphibole Group
Double Chain Structure
Mica Group Clay Group
Sheet Structure
Quartz Feldspar Group
Framework Structure
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Systematic SilicateMineralogy
Ratio of Tot. Atoms to Iron
Silicon
13½ 17 15 15 lt135
141/3 lt140 14 (0) 13
(0) 141/3 (0) 16 ½
Olivine

• Fig. 2.9
• From bottom to top
• Increasing Fe/Mg/Ca
• Decreasing silica
• Increasing density
• Darker minerals

Pyroxene Group
Amphibole Group
Mica Group
Decreasing Silica
Increasing Fe/Mg/Ca
Quartz K and Na Feldspar Ca Feldspar
Increasing Density
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Systematic SilicateMineralogy
Olivine
Mantle

• Fig. 2.9
• From bottom to top
• Increasing Fe/Mg/Ca
• Decreasing silica
• Increasing density
• Darker minerals

Pyroxene Group
Oceanic Crust
Increasing
Amphibole Group
Fe/Mg/Ca Density Weathering
Melting and crystallizing Temperature
Mica Group
Decreasing
Cont. Crust
All of these silicates weather to form Clay
Minerals Except quartz
Quartz K and Na Feldspar Ca Feldspar
Quartz melts first
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Other Important Rock-Forming Minerals

• Sediments and Sedimentary Rocks
• Quartz resistant to alteration by weathering
• Clay most other silicates weather to clay
• Carbonates (non-silicates) Deposited in shallow
  tropical seas be shellfish and coral
• Calcite CaCO3
• Dolomite CaMgCO3
• Halite Deposited by evaporating seas
• Single Element Minerals Diamond, Graphite, Gold,
  sulfur