Download Minerals and Their Physical Properties

The Chemistry of Color
Why do minerals
have different colors?
Definition of a Mineral

Minerals are naturally-occurring, inorganic
substances with a definite and predictable
chemical composition and crystalline
structure.
Mineral Properties

Predictable physical properties

Controlled by chemical composition
and/or structure
Mineral Properties

Color

Streak: Color of the mineral when powdered

Luster: The character of light that is reflected

Cleavage/Fracture: The way the mineral breaks

Habit: The form in which the mineral grows

Hardness: Resistance to being scratched

Specific Gravity

Miscellaneous Properties: e.g., smell, magnetism
Generalized Atomic Structure

Nucleus houses the massive
particles (protons and neutrons)




# Protons = Atomic Number
# Protons + Neutrons = Atomic Mass
Responsible for mass and density
Electrons lie in orbitals that
surround the nucleus


# Electrons = # Protons
 If not, then it is an ION
Responsible for bonding
Ions

Ions are electrically charged particles formed by
the gain or loss of electrons


Cations are positively charged
Anions are negatively charged

Metals are elements that readily form cations

Non-Metals are elements that readily form
anions
Electron Orbitals
Alkali Metals
Alkali Earth Metals
Transition Metals
Metaloids
Other Metals
Non-Metals
Halogens
Noble Gases
Decreasing Atomic Radius
Decreasing Atomic Radius
Electronegativity: measure of an atom’s
ability to attract electrons in a chemical bond
Ionic Bonds

An atom with lower
electro negativity
transfers one or more
electrons to an atom with
higher electronegativity
 Metal with non-metal

Results in charged ions

Oppositely charged ions
are attracted and thereby
form a weak bond
Ionic Bonds

Ions are not actually
“attached” and so bonds
are relatively weak
 What property?

Ions can be attracted by
other charged ions or
molecules such as water
 What property?
Ionic Bonds

Ions are not actually
“attached” and so bonds
are relatively weak
 Soft minerals (easily
scratched)

Ions can be attracted by
other charged ions or
molecules such as water
 What property?
Ionic Bonds

Ions are not actually
“attached” and so bonds
are relatively weak
 Soft minerals

Ions can be attracted by
other charged ions or
molecules such as water
 Soluble in water
Ionic Bonds and Solubility

Electronegativty of H: 2.1

Electronegativty of O: 3.5

Uneven sharing of
electrons
 Due to shape of water
molecule, one end (O)
http://upload.wikimedia.org/wikipedia/commons/0/05/H2O_molecule_scheme_of_dipole
tends to be negative
whereas the other end (H)
tends to be positive
Ionic Bonds
and
Solubility
OH+
H+
H+
Na+
Cl-
OH+
Cl-
Na+
Na+
Cl-
O-
Ionic Bonds
and
Solubility
H+
H+
H+
Cl-
OH+
H+
H+
O-
O-
H+
H+
Na+
H+
OCl-
H+
H+
O-
H+
Common Ionic Minerals

Halite (NaCl): Halide
Table Salt, De-Icer

Calcite (CaCO3): Carbonate
Chalk, Plaster, Toothpaste,
Antacids

Gypsum (CaSO4•H2O): Sulfate
Drywall, Cement, Plaster
Covalent Bonds

Two atoms with
approximately equal
electronegativity share
one or more electrons

Results in a merging of
the electron clouds, and
thereby forms a strong
bond
 What property?
Covalent Bonds

Two atoms with
approximately equal
electronegativity share
one or more electrons

Results in a merging of
the electron clouds, and
thereby forms a strong
bond
 Hard minerals
Common Covalent Minerals

Quartz (SiO2): Silicate
Abrasive, Glass

Feldspar (NaAlSi3O8 ): Silicate
Ceramics, Household Cleanser

Garnet (Fe3Al2Si3O12 ): Silicate
Sandpaper
Relative Bond Strengths



Na Ion: +1
Bonds: 6
Bond Strength: 1/6
• Si Ion: +4
• Bonds: 4
• Bond Strength: 4/4=1
Covalent Bonds in Silicates Are Stronger than Ionic Bonds
Metallic Bonds

Delocalized sharing of
free electrons among a
lattice of metal atoms
with little or no difference
in electronegativity

Results in one continuous
electron cloud in which
electrons are free to
move
 Soft, malleable
minerals that conduct
both heat and
electricity
Metallic Bonds

Delocalized sharing of
free electrons among a
lattice of metal atoms
with little or no difference
in electronegativity

Results in one continuous
electron cloud in which
electrons are free to
move
 What properties?
Van der Waal’s “Bonds”

Attraction between
atoms, ions or molecules
that have an imbalance in
the distribution of
electrons (dipole)

Fleeting and fluctuating
weak attractions
 Soft minerals with a
low melting point
 Allows for the basal
cleavage in micas
Common Van der Waals Minerals

Talc (Mg3Si4O10(OH)2 ):
Silicate
Baby Powder, Paint, Paper

Graphite (C ): Element
Pencil Lead, Dry Lubricant
Chemical Bonding
Why do minerals
have different hardness?
Definition of Light

Light is electromagnetic radiation.

Light exhibits properties of both a particle (e.g.,
ability to travel through a vacuum) and a wave
(e.g, interference and polarization)

For understanding behavior of light in minerals
we can focus on the wave properties of light
Aspects of Light

Amplitude (height of wave) corresponds to the intensity
(brightness) of light

Wavelength corresponds to the energy of light
 In the visible spectrum wavelength corresponds to
color
Wavelength of Light



Visible light is only a
tiny, moderate energy
fraction of the
electromagnetic
spectrum
Longer wavelengths
(e.g., radio waves)
have less energy
Shorter wavelengths
have more energy
Absorption Results in Color
(A Familiar Example from Biology)
Why is the Visible Spectrum Visible?
What Color?

What is the color of a mineral that absorbs
green and yellow light?

What spectral colors are absorbed by a
yellow mineral?
What Color?

What is the color of a mineral that absorbs
green and yellow light?


Purple
What spectral colors are absorbed by a
yellow mineral?
What Color?

What is the color of a mineral that absorbs
green and yellow light?


Purple
What spectral colors are absorbed by a
yellow mineral?

All but yellow
Absorption and Emission of Light
Color and Compositon

Certain elements are strong pigmenting
agents and produce strongly colored
specimens when they are present,
whether as a part of the crystal lattice or
as an impurity.

These elements are termed the
chromophores.
Color and Compositon

Chromium (Cr): orange, green

Cobalt (Co): pink, purple, blue

Copper (Cu): blue, green

Iron (Fe): red, green, yellow

Manganese (Mn): pink
Transition Metals
What Color?

Rhodonite (MnCO3)?

Crocoite (PbCrO4)?

Malachite (Cu2CO3[OH]2)?
What Color?

Rhodonite (MnCO3)?

Crocoite (PbCrO4)?

Malachite (Cu2CO3[OH]2)?
What Color?

Rhodonite (MnCO3)?

Crocoite (PbCrO4)?

Malachite (Cu2CO3[OH]2)?
What Color?

Rhodonite (MnCO3)?

Crocoite (PbCrO4)?

Malachite (Cu2CO3[OH]2)?
Color vs Streak

If the color of a mineral is due to a major
constituent of the mineral (%), the color
and streak will be similar

If the color of a mineral is due to a trace
constituent of the mineral (ppm), then the
streak will be pale or white
Generalized Atomic Structure

Nucleus houses the massive
particles (protons and neutrons)




# Protons = Atomic Number
# Protons + Neutrons = Atomic Mass
Responsible for mass and density
Electrons lie in orbitals that
surround the nucleus


# Electrons = # Protons
 If not, then it is an ION
Responsible for bonding
Ions

Ions are electrically charged particles formed by
the gain or loss of electrons


Cations are positively charged
Anions are negatively charged

Metals are elements that readily form cations

Non-Metals are elements that readily form
anions
Electron Orbitals
Alkali Metals
Alkali Earth Metals
Transition Metals
Metaloids
Other Metals
Non-Metals
Halogens
Noble Gases
Decreasing Atomic Radius
Decreasing Atomic Radius
Electronegativity: measure of an atom’s
ability to attract electrons in a chemical bond
Ionic Bonds

An atom with lower
electro negativity
transfers one or more
electrons to an atom with
higher electronegativity
 Metal with non-metal

Results in charged ions

Oppositely charged ions
are attracted and thereby
form a weak bond
Ionic Bonds

Ions are not actually
“attached” and so bonds
are relatively weak
 What property?

Ions can be attracted by
other charged ions or
molecules such as water
 What property?
Ionic Bonds

Ions are not actually
“attached” and so bonds
are relatively weak
 Soft minerals (easily
scratched)

Ions can be attracted by
other charged ions or
molecules such as water
 What property?
Ionic Bonds

Ions are not actually
“attached” and so bonds
are relatively weak
 Soft minerals

Ions can be attracted by
other charged ions or
molecules such as water
 Soluble in water
Covalent Bonds

Two atoms with
approximately equal
electronegativity share
one or more electrons

Results in a merging of
the electron clouds, and
thereby forms a strong
bond
 What property?
Covalent Bonds

Two atoms with
approximately equal
electronegativity share
one or more electrons

Results in a merging of
the electron clouds, and
thereby forms a strong
bond
 Hard minerals
Metallic Bonds

Delocalized sharing of
free electrons among a
lattice of metal atoms
with little or no difference
in electronegativity

Results in one continuous
electron cloud in which
electrons are free to
move
 Soft, malleable
minerals that conduct
both heat and
electricity
Metallic Bonds

Delocalized sharing of
free electrons among a
lattice of metal atoms
with little or no difference
in electronegativity

Results in one continuous
electron cloud in which
electrons are free to
move
 What properties?
Natural Bonds Usually Share
Characteristics
Van der Waal’s “Bonds”

Attraction between
atoms, ions or molecules
that have an imbalance in
the distribution of
electrons (dipole)

Fleeting and fluctuating
weak attractions
 Soft minerals with a
low melting point
 Allows for the basal
cleavage in micas