Download Lecture 4 - Minerals - Florida Atlantic University

Minerals
Building Blocks of Rocks and
Economic Resources
GLY 2010 - Summer 2014
Lecture 4
1
Minerals
• Minerals are a
major building
block of most
rocks
• Their properties
determine a
good part of the
physical
behavior of the
earth
2
Mineral Definition
• Naturally occurring
• Inorganic
• Crystalline
3
Crystal Structure Examples
Halite
Fluorite
4
Formation of Halite
5
Atoms
6
Atomic Terminology
• The atomic number equals the
number of protons.
 Thus Hydrogen, with one proton, has
atomic number 1, and iron, with twentysix protons, has atomic number 26.
• The atomic weight equals the number
of protons plus the number of neutrons.
 If an iron atom has 26 protons, and 30
neutrons, it has an atomic weight of 56.
7
Chemical Elements
• An element is composed of atoms with
the same atomic number
• Each element has a unique chemical
symbol
8
Isotopes
• An isotope of an element is an atom with
the correct number of protons for that
element, plus a fixed number of neutrons
 Example: Carbon has three isotopes, each
with six protons, and with 6, 7, or 8
neutrons
9
Stable or Radioactive
• An isotope may be stable or radioactive
 Carbon isotopes with 6 or 7 neutrons are stable, while the
isotope with 8 neutrons is radioactive
10
Chemical Symbols
• Atomic number is shown as a subscript
before the element symbol - 1H
• The atomic weight is shown as a
superscript before the symbol - 56Fe
11
Examples of Chemical Symbols
• Particular isotopes are shown using a
superscript in front of the symbol
 1H is normal hydrogen, with one proton
and no neutrons
 2H is deuterium, with one proton and one
neutron
 3H is tritium, with one proton and two
neutrons - it is radioactive
12
Ions
• Ions are charged
particles
• Cations: Atoms that
lose one or more
electrons become
positively charged
 Anions: Atoms that gain one or more electrons are
negatively charges
 Ionic charge: Shown by a superscript after the
chemical symbol, O213
Use of Isotopes
• Chemical tracers
 Study topics such as:
• Pollution
• Formation temperature
• The path of volcanic emissions, etc
• Radioactive isotopes are used in
estimating the age of materials
14
Compounds
• Combination of two or more atoms
• Combination is called a molecule
 Water H2O
 Carbon dioxide CO2
15
Molecules
• Molecules may consist of just one element
 Oxygen in the atmosphere is O2
• Molecules may consist of several elements, in
various amounts
 Example: Plagioclase feldspar, the most common
mineral on earth NaAlSi3O8 - one sodium (Na),
one aluminum (Al), three silicons (Si), and eight
oxygens (O)
16
Chemical Bonds
• The “glue” that holds materials together
• Responsible for the properties of matter
 On an atomic scale
 At the scale of the earth
• When two atoms combine to form a chemical
bond, energy is released
17
Types of Bonds
•
•
•
•
•
Ionic
Covalent
Metallic
Hydrogen
Van der Waals
18
Ionic Bonds
• Bonds between a cation and an anion
• They occur when a cation donates one or
more electrons to an anion
• They are strong
• Dissolve in water
 Halite, or table salt, for example
19
Covalent
Bonds
• Equal sharing of electrons by two atoms
• Very strong bonds
• Compounds usually have limited
solubility
• May create molecules that do not readily
combine to form larger particles
 Ex. Carbon dioxide is strongly bonded
within the molecule, but weakly bonded
between molecules, so it is a gas
20
Metallic Bonds
• Outer electrons are loosely held
• Properties: Opaque, may have a metallic luster
• Bond strength is moderate
21
Hydrogen Bonds
• Secondary bond
between oxygen on
one water molecule
and hydrogen on
another
Hydrogen bonding in water
22
Van der Waals Bonds
Diamond
Graphite
• Residual, extremely weak bonds form by
distortion of electron clouds by the presence of
a nearby atom
23
Molecular Properties
• Molecules - as strong as the
weakest bonds within themselves
24
Mineral Properties
• Depend on the type and strength of bonds and
number of bonds (bond density) within
themselves
• Minerals will be examined in the laboratory,
and most properties will be taught there
• Examples of mineral properties: hardness,
cleavage
25
Hardness
• A mineral’s hardness is measured by the
ability of a surface to resist abrasion
26
Moh’s Scale of
Hardness
 Any higher number
mineral will scratch any
lower number.
Moh’s scale is not linear –
the difference in hardness
between low numbers is
much less than between high
numbers
27
Cleavage
• When a
mineral always
or usually
breaks along a
particular
plane, it is said
to have a
cleavage plane
28
Two-directional Cleavage
• Selenite, a variety
of the mineral
gypsum, shows
cleavage in two
directions
29
Angle Between Cleavage Planes
30
Three-directional Cleavage
• Halite, common
table salt, shows
three directions of
cleavage at right
angles
31
Three-directional Cleavage
• Calcite shows
three directions
of cleavage, not
at right angles
32
Four Directional Cleavage
33
Crystal and Crystal Faces
Apatite, showing a hexagonal prism these are crystal faces, not cleavage
planes
34
Identification of Minerals
• Minerals are identified based on their
physical and chemical properties
• A combination of properties are
needed, just as no single line from a
fingerprint can identify a person
35
Mineral Classification
• Classification is based on anion type
 Minerals with the same anions have similar
properties, while those with the same
cations often do not
36
Anions
• Anions may be a single ion
 Ex. Oxygen O2-
• Anions are often groups of atoms, with
the entire group having a negative charge
 Ex. Carbonates are CO32- , one carbon with
three oxygens, and the whole group with a
minus 2 charge
37
Common Anion Groups
•
•
•
•
•
Silicates, SiO44Oxides, O2Sulfides, S2Carbonates, CO32Phosphates, PO4338
Occurrence of Minerals
• Over half of all known minerals are silicates,
because oxygen is the most common element
on earth, and silicon is the second most
common.
• Silicates are the most important type of rockforming minerals, those minerals that make up
most of the earth’s rocks
• Most silicate minerals contain other elements
in addition to silicon and oxygen
39
Silicon Tetrahedron
• The SiO44tetrahedron is the
basic building block
of silicate minerals
40
Silicate
Structures
41
Chemistry of the Continental Crust
• Eight elements account
for almost all of the
earth’s crust
• Chart is based on weight
percent
• Oxygen is the most
abundant, and silicon
the second, which is
why most minerals are
silicates
42
Felsic Minerals
• Minerals with a lot
of aluminum and
silicon are light in
color, and are called
Felsic
• Plagioclase
feldspar, the
most common mineral in
the earth’s crust
43
Mafic Minerals
• Minerals with more
iron and magnesium,
and less silicon, are
dark in color and are
called Mafic (from
the first two letters of
magnesium and the
first letter of ferium)
• Augite, a type of pyroxene
44