What is a Mineral?
What Exactly is a Mineral?
• Compositionally and
physically distinct
substance
• Four criteria to be a
true mineral…
Naturally Occurring
Created through natural geologic processes
Synthetic diamond: not a mineral
Raw diamond: mineral
Inorganic
That is, they do not consist of
carbon-hydrogen molecules that may
also form crystalline substances
through biological processes
Sugar: It looks like a mineral, but is it?
Nope. Note the C-H bonds.
Solid
Liquid water
Not a mineral
Snowflake—frozen water
Mineral…believe it or not
Definite Chemical Composition
Minerals are complex assemblages of multiple elements
Chemical Formula
Types of atoms involved and relative proportions
Ex. Quartz
Chemical formula
SiO2
Ex #2: Elbaite
Chemical formula
Na(Li,Al)3Al6(BO3)3Si6O18(OH)4
Elements
• Pure chemical substance composed of one
type of atom (i.e. specific # of protons…)
• 88 naturally occurring elements
• Most common (i.e. compose 98% of the
earth’s crust—and therefore, minerals)
– Oxygen, silicon, aluminum, iron, calcium,
magnesium, potassium, and sodium
Atomic Structure
• Atom
– Basic unit of an element
– Very, very, very small
(1/10,000,000,000 m)
– Nucleus
– Protons (+)
– Neutrons (neutral)
– Electrons (-)
– “cloud” surrounding
nucleus—exist in “shells”
– Mostly empty space
Visualizing the size of an atom
• The nucleus is very
small compared to the
overall size of an atom
• Imagine 5 ½ football
fields (minus end zones)
placed end to end (100
yrds long x 160’ wide)
• Nucleus is like a grain of
sand in the middle of
them
It’s All About the Electrons, Baby…
• A stable atom is one in
which the outermost
shell of electrons is
completely filled
• Atoms can fill their
outer shells by bonding
to other atoms
– Ionic bonding
– Covalent bonding
Bonding in a [Nut] Shell…
• Ionic Bonding
– Cations (atoms that have
lost an electron) are
attracted to anions
(atoms that have gained
an extra electron)
– Neutral compounds
– Weaker but more
common than covalent
bonds
Bonding in a [Nut] Shell…
• Covalent bonding
– Two or more atoms
share their electrons,
producing the effect of
filled outer electron
shells
– Very strong bond
Crystalline Structure
• Arrangement of atoms
are
–
–
–
–
Fluorite
Orderly
Regular
3-D
Repeating pattern
Biotite
Halite
Can You Spot the Mineral Wannabes?
Pyrite
FeS2
Silicon Carbide
SiC
oil
Chalcanthite
CuSO4-5H2O
Growing a Mineral
• Unit cell—smallest unit
structure of a mineral
• Brick Wall example
Growing a Mineral: Halite
Halite unit cell
Halite crystal
What halite looks like to
us
Identifying a Mineral
• All minerals have
physical and chemical
properties that can be
easily recognized
• Direct result of
structure and
composition
•
•
•
•
•
•
•
Crystal habit
Cleavage
Fracture
Hardness
Color
Streak
Luster
Cleavage
• Not the kind you’re
thinking of…
• The tendency of a
mineral to break along
flat surfaces
• Governed by bond
strength and crystal
structure
• Stronger bonds = poor
or no cleavage→
Oooo…shiny!
• Luster
– The way a mineral reflects
light
• A metallic mineral is said
to have a metallic luster
• Those that do not have a
metallic luster (nonmetallic) are assigned
names that are selfexplanatory
Pyrite has a metallic luster
– Pearly, resinous, earthy,
glassy, etc…
Quartz has a glassy luster
School of Hard Knocks…
• Hardness
– Resistance of a mineral to
scratching
• Hardness can be
determined by scratching
mineral with an object of
known hardness
• Scale—Mohs
–
Based on 10 minerals: 1
being talc and 10 being
diamond