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Introduction to Minerals
Questions…
• Why learn about minerals?
– They are the source of great wealth and beauty.
– Minerals provide clues about the geologic past.
• How could knowing about minerals assist
you in buying a home?
– Some minerals are very unstable when exposed
to water and air.
• How do minerals form?
DEFINITION OF A MINERAL
•naturally occurring
•inorganic
•solid
•orderly internal structure (crystal)
•with a definite chemical composition.
(can vary within a specified range)
MINERAL CLASSIFICATION
•Minerals are classified based on their:
– Physical properties
–Chemical composition
– Crystal Structure
ATOMIC STRUCTURE OF MATTER
•Elements
–Form of matter than cannot be reduced to a simpler
form by heat, cold, or chemical reactions.
•Atoms – basic form of an element.
–Protons – positive charge particle in the nucleus
–Neutrons – neutrally charged particle in the nucleus
–Electrons – negatively charged particle outside the
nucleus.
CHEMICAL
ELEMENTS
pure substances that cannot be decomposed by ordinary
means to other substances.
Aluminum
Sodium
Bromine
Chemical Symbols
Atoms
Electron energy levels
CHEMICAL COMPOUNDS are
composed of atoms and so can be
decomposed to those atoms.
The red compound is
composed of
• nickel (Ni) (silver)
• carbon (C) (black)
• hydrogen (H) (white)
• oxygen (O) (red)
• nitrogen (N) (blue)
Compounds
– composed of 2 or
more elements in
a fixed ratio
– properties differ
from those of
individual
elements
– EX: table salt
(NaCl)
A MOLECULE is the smallest unit of a compound
that retains the chemical characteristics of the
compound.
Composition of molecules is given by
a MOLECULAR FORMULA
H2O
C8H10N4O2 - caffeine
Octet Rule = atoms tend to gain, lose or share electrons so
as to have 8 electrons (All atom aspire to be “NOBLE”)
C would like to Gain 4 electrons
N would like to Gain 3 electrons
O would like to Gain 2 electrons
1). Ionic bond – electron from Na is transferred to Cl,
this causes a charge imbalance in each atom. The Na
becomes (Na+) and the Cl becomes (Cl-), charged
particles or ions.
2. Covalent bonds-
Two atoms share one or more pairs of outer-shell
electrons.
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)
Double and even
triple bonds are
commonly
observed for C,
N, P, O, and S
H2CO
SO3
C2F4
- water is a polar molecule because oxygen is more
electronegative than hydrogen, and therefore electrons
are pulled closer to oxygen.
Ice (water crystals) takes up more
space than liquid water because of
hydrogen bonding
Metallic Bonding- electrons flow
freely around metal atoms
The balance of energy
• Atoms have a desire to have their outermost
energy level full of electrons, otherwise a
“lone” electron may be lost to other
elements or may be paired with a “lone”
electron from another atom.
• Think of a teeter-totter with only one
person, or one with an unbalanced number
of participants.
Periodic Table
http://www.webelements.com/webelements/scholar/index.html
Atomic number –
Number of protons
and electrons
Periodic Table
Tendency to lose outer electrons in order to become more “stable.”
Periodic Table
Tendency to gain outer electrons in order to become more “stable.”
Periodic Table
Transition elements – also known as the heavy metals
Tend to share electrons to become stable
Periodic Table
Inert gases, which are already stable and don’t need additional electrons
MINERAL COMPOSITION
•Minerals are made of different ions
bonded together (gain, lose, or share
electrons)
•Ions are charged atoms.
Figure 2.4, Page 28
Chemical Bonding of
Sodium (Na) and Chlorine (Cl)
Diagrammatic arrangement of
sodium and chlorine ions in table
salt
Sharing of electrons between two
chlorine ions to for a molecule of
chlorine gas (Cl2)
Stacking ions to form different
crystal structures
From atomic theory to a real crystal
In Minerals (Crystals)
Physical Arrangement
is more important than
Chemical Composition
BONDING IN MINERALS
•Ionic bonding
opposite charges attract (gain or lose
electrons)
•Covalent bonding
–ions share electrons
•Metallic bonding
–free moving electrons
Atomic Structure of Minerals
•Arrangement of atoms or ions in an orderly,
repeating three-dimensional array.
(Gases)
Atomic Structure of Minerals
•External shape is a reflection of the
internal crystal structure.
halite
diamond
staurolite
quartz
W. W. Norton
garnet
stibnite
calcite
kyanite
Atomic Structure of Minerals
• Polymorphism - diamond and graphite
Two Minerals from a Single Element
Diamond and Graphite
Atomic structure can lead to
symmetry in some minerals
Atomic structure can
lead to symmetry in
some minerals
Halite
What is the difference between a
mineral and a rock?
• Rocks are made up of more than one
mineral
– Example: Granite contains the minerals quartz,
plagioclase, and mica.
• Minerals contain a specific chemical
composition
– Example: Quartz - SiO2
Growth and Destruction of
Minerals
• Growth occurs through crystallization,
which is the addition of atoms to a crystal
face, in a liquid environment.
– Requires: (1) sufficient quantity of the ions, (2)
proper temperature and pressure (space).
• Growth generally occurs in a confined
space. Thus, external shape may not reflect
internal structure.
ROCK-FORMING MINERALS
•Silicates
•Carbonates
•Sulfates
•Halides
Silicates
•Silica Tetrahedron
–1 silicon ion bonded to 4 oxygen
ions
•Silicon is positively charged (+4)
•Oxygen is negatively charged (-2)
•Net charge on tetrahedron : -4
•(SiO44-)
More details on the Silicates
• Make up 95% of the Earth’s Volume
• Basic structural shape is the tetrahedron,
which defines the mineral groups:
–
–
–
–
–
Isolated tetrahedron (olivine)
Single chain (pyroxene - augite)
Double chain (amphibole)
Two-dimensional sheet (micas, clays)
Three-dimensional framework (quartz, feldspars)
Clay minerals
• Form at or near Earth’s surface in the
presence of air and water from the
breakdown of other silicates
• Sheet silicates like the micas.
• Very small crystals.
• Low density
– Example: kaolinite
Isolated tetrahedron
Isolated
Isolated tetrahedron (olivine)
-Does not break a certain way
Isolated tetrahedron
Single Chain
Single chain (pyroxene - augite)
-Breaks on 2 planes at right angles
Isolated tetrahedron
Double Chain
Double chain (amphibole hornblend)
-Breaks on 2 planes at 60° and 120°
Isolated tetrahedron
Two dimensional sheet
Two-dimensional sheet (micas muscovite)
-Breaks in 1 plane
Isolated tetrahedron
Three dimensional framework
Three-dimensional framework
(quartz, feldspars - orthoclase)
-Breaks on 2 planes at 90°
MINERAL IDENTIFICATION
Color
Streak
Fracture
Habit
Specific Gravity
Hardness
Luster
Cleavage
Taste
Smell
Magnetic
Effervescence
–Mohs Hardness Scale
Bowen’s Reaction Series
the realationship between temperature and
the formation of crystals in magma
1400 oC
Olivine
Pyroxene
Amphibole
Biotite
Mafic
Calcium-rich
Plagioclase
Sodium-rich
Intermediate
Orthoclase
Muscovite
800 oC
Quartz
Felsic
Crust composition – most
common elements
Mafic
• Minerals rich in iron and magnesium
• Representative of high density, high
temperature magmas.
• Examples:
– Olivine, pyroxenes, amphiboles
Felsic minerals
• Minerals rich in silicon and aluminum.
• Representative of low density, low
temperature magmas.
• Examples:
– Feldspars, quartz, micas
Mineral Destruction
• Minerals can melt under high temperatures,
removing of outer atoms - melting
• Under high pressures, some minerals melt, while
others may partially melt, resulting in same
chemical composition, but different crystal
structure.
• Weathering - physical and chemical breakdown of
minerals
– Some atoms can be pried loose from the structure by
water – dissolving (example: NaCl)
Carbonates
• Basic structure contains the strong, covalent
bonded carbonate ion CO32– Bonds easily (ionic) with metals, such as
calcium to form calcium carbonate or calcite
(CaCO3) CaCO3 is often precipitated directly
from carbonate rich seawater.
– Shell organisms capture carbonate and combine
it with calcium to form CaCO3.
Carbonates #2
• Most common mineral is calcite and found readily in
limestone and dolomite rock.
• Calcite is relatively soft, 3-4 on Mohs hardness scale, and
can dissolve in acids (even mild carbonic acid).
– Results in cave formation
– Weathering of statues and buildings due to acid rain.
• Calcite is one mineral that easily deforms and reforms at
the Earth’s surface. Often find calcite crystals in the cracks
of rocks
• Calcite can be easily mistaken for quartz, but a scratch test
can remedy the dilemma.
• Dolomite (CaMg(CO3)2 bonds a little more tightly with
two carbonate ions, resulting in more resistance to acid
destruction.
Sulfates
• Gypsum (CaSO4 ·2H2O)
• Anhydrite (CaSO4) – note the two missing water
molecules, hence the “An” in the mineral name.
Plaster contains anhydrite.
• Barite (BaSO4) is soft and “greasy” feeling. Since
it doesn’t burn under intense friction, barite serves
as an excellent lubricant for drilling.
Halides
• Common Salt (NaCl)
– Halite
• Found in thick layers where ancient seas
have since evaporated.
Elements as Minerals
•
•
•
•
•
•
Sulfur
Gold
Silver
Platinum
Diamond
Many of these metals are often associated
with sulfide minerals and low temperature
silicates (e.g. quartz veins).
References
• The Mineral Gallery (commercial site)
– http://mineral.galleries.com/