Download Document

III. Atoms, Elements and 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)
 C. The silicate minerals (7)
 D. Other important rock-forming minerals (4)
 E. Mineral properties

A. Changing Scale: Zooming in from global view to atomic scale
Quartz
Biotite
Feldspar
The crust is made of rocks > Rocks are made of minerals > …
A. Changing Scale: Zooming in from global view to atomic scale
Rocks are made of minerals > Minerals are made of atoms
Atoms and Elements

Nucleus

Protons



Neutrons




+ Charge
Has Mass, Atomic #
0 Charge
Mass same as One Proton
Atomic Mass #
Electrons



In shells (2, 8, 8…)
- charge (balances each
proton +)
Very little Mass
Electron
Shells
Ions


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)
Ions

Other Common
Examples
Sodium

Sodium, at.# 11
{2, 8, 1}  Na+ (Cation)

Oxygen, at.# 8
{2,6},  O-2

Silicon, at.# 14
{2,8,4}  Si+4
Oxygen
Most Common Elements of
Earth’s Crust
Oxygen:
Silicon:
Aluminum:
Iron:
O-2
Si+4
Al+3
Fe+2 or +3
Calcium: Ca+2
Sodium: Na+1
Potassium: K+1
Magnesium: Mg+2
B. Introduction to Minerals

Halite (Rock Salt)




Mineral mined for rock
salt and table salt
Na gives electron to Cl
Opposites attract,
elements bond
NaCl (Sodium Chloride)
Intro to Minerals



Repeating 3-D pattern
forms a Crystalline Solid
(or Crystal)
Naturally occurring
Crystal Form
crystals are Minerals
Crystalline structure and
bonding leads to physical
properties: hardness,
crystal form, cleavage
specific gravity (density)
(pg. 38-43)
3 planes of cleavage
Some Familiar Crystal Forms

Quartz Crystal
(SiO2)
Fig. 2.15a

Snow Flake (Ice Crystal) due
to crystalline structure of H2O
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
Silica Tetrahedra

The building block of
most common rock
forming minerals




Four O2- in a tetrahedral
configuration
One Si4+ nested in the
center
(4  -2) +4 = -4
(SiO4)-4
-4
C. Silica Tetrahedra and Silicate
Minerals



Si and O bond in a
tetrahedron shape
The basic building block
of most minerals of the
crust
Bond with other
tetrahedra and cations to
form Silicate Minerals
Definition of Mineral




Naturally Occurring
Crystalline
Solid
With a definite chemical
composition


A unique composition
or
A definite range of compositions
Mineral Group, e.g. Olivine
Silicate Minerals: Examples
E.g., Olivine

Isolated silicate
structure
(SiO4)-4 + 2×Fe+2
Fe2SiO4

Fe Mg SiO4

Mg2SiO4



Definite Range

(Fe,Mg) 2 SiO4  Olivine Mineral Group
Silicate Minerals: Examples

E.g., Olivine




Isolated silicate
structure
bonded with Fe
and/or Mg
Makes up much of
Earth’s mantle
Fe/Mg rich (Ferromagnesian mineral)


2/7 = 0.29 = 29%
Silica poor

1/7 = 0.14 = 14%
% of all atoms
Silicate Minerals: Examples

E.g., Pyroxenes (Mineral Group)

Single Chain Silicate structure
(SiO3)-2 + Fe+2
FeSiO3

(Fe,Mg) SiO3


MgSiO3
(Fe,Mg) SiO3  Pyroxene



Mineral Group
Ferromagnesian
Silicate Minerals: Examples

E.g., Pyroxenes (Group of
minerals)





Single Chain Silicate structure
bonded with Fe, Mg, Ca, and Al
Found in Oceanic Crust
Fe/Mg/Ca rich (20%)
Silica poor
(<20%)
Single Chain Silicates

E.g., Pyroxenes (SiO3)
Silicate Minerals: Examples

E.g., Amphiboles (Group of
minerals)




Double Chain Silicate structure
bonded with Fe, Mg, Ca, and Al
Found in Continental Crust
More silica and less iron than
pyroxenes
Double Chain Silicates

E.g., Amphiboles (Si8O22)
Silicate Minerals: Examples

E.g., Micas (Muscovite and Biotite)


Sheet Silicate structure
bonded with Al, K,
(biotite has Fe, Mg)


Found in Continental Crust
More silica and less iron than
Amphiboles
Sheet Silicates

E.g., Micas (Biotite and Muscovite) (AlSi3O10)
Common
Framework Silicates

Feldspar Group




The most common minerals in the crust of the earth
Oceanic Crust: Ca Plagioclase (dark)
Continental Crust: K feldspar (pink) and
Na Plagioclase (white)
Quartz





Pure Silica SiO2
Stable under many conditions
Not easily weathered
Melts at a low temperature
Continental Crust and Sediments
Framework Silicates

E.g., Quartz (SiO2) and Feldspars (AlSi3O8)
Framework Silicates

E.g., Quartz (SiO2) and Feldspar (AlSi3O10)
% of Tot. # of atoms
Fe/Mg: Silicon:
Olivine
29%
14%
Systematic Silicate
Mineralogy


Pyroxene
Fig. 2.9
<20%
Group
From bottom to
top



Decreasing
Silica
Increasing
Fe/Mg/Ca
Increasing
Density

Amphibole
Group
<3%
Increasing
Fe/Mg/Ca
Decreasing silica
Mica
<2%
Group
Increasing density
Darker minerals
Quartz
K and Na Feldspar
Ca Feldspar
(0)
(0)
(0)
20%
23%
25%
33%
23%
15%*
Other Important
Fig. 2.22
Rock-Forming
Minerals

Sediments and Sedimentary Rocks




Quartz: resistant to alteration by weathering
Feldspar: moderately resistant to 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
Important Economic Minerals
Fig. 2.13

Elements:




Diamond, Graphite,
Gold, Copper
Sulfur
Iron Oxides:


Hematite (Fe2O3),
Magnetite (Fe3O4)
Fig. 21.1
E. Physical
Properties
Fig. 2.20
Cleavage
Pyroxene
Amphibole
Mica
Quartz
Halite
Calcite
2 planes,
splinters
Crystal
Form
Prismatic
(Needles)
Hardness
6 (File)
Fig. 2.19a
E. Physical
Properties
Cleavage
Pyroxene
Amphibole
Mica
Quartz
Halite
Calcite
2 planes,
splinters
1 plane
Crystal
Form
Prismatic
(Needles)
Plates
Hardness
6 (File)
2 (fingernail)
Fig. 2.15a
E. Physical
Properties
Cleavage
Pyroxene
Amphibole
Mica
2 planes,
splinters
1 plane
Crystal
Form
Prismatic
(Needles)
Plates
Quartz
None
Columnar
Halite
Calcite
Hardness
7
6 (File)
2 (fingernail)
E. Physical
Properties
Cleavage
Pyroxene
Amphibole
Mica
2 planes,
splinters
1 plane
Crystal
Form
Prismatic
(Needles)
Plates
Hardness
Quartz
None
Columnar
7
Halite
Calcite
3 planes
Cubes
Rhombs
2½
3 (Penny)
Fig. 2.15a
6 (File)
2 (fingernail)