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Chapter 4.1 – Minerals and Their Properties
• Minerals are the building blocks of rocks
(which are usually mixtures).
• Minerals are pure substances - elements or
compounds, with specific chemical formulas that
do not vary or only vary within a limited range.
• About 3000 minerals are known.
• Only about 10 are common in Earth's crust.
• Most minerals form in the geosphere, but some
minerals form in the hydrosphere or even the
biosphere.
What is a Mineral?
The 3 criteria:
1) Naturally
occurring
substance, not
manmade.
2) Inorganic – not
made of anything
that is/was living.
3) Solid and
Crystalline in
form.
What does “crystalline” mean?
The particles in minerals (atoms, ions, or
molecules) are arranged at specific “lattice”
positions.
The shape of a mineral crystal can reflect the
internal structure but often does not.
What does “crystalline” mean?
Remember…a mineral can also be crystalline at the
atomic scale without exhibiting crystal-like shapes.
It is still a “crystal”.
Mineral Properties help you to
identify minerals!
Characteristic property - A physical or
chemical property that is helpful in identifying
a material (in this case, minerals).
Ex. – Diamond’s extreme hardness and luster
Ex. – Graphite’s greasy feel, softness,
and metallic luster.
Mineral Properties help you to
identify minerals!
Physical property – A quality that can an be
measured without a chemical reaction
occurring.
Ex. Color, crystal shape, luster, hardness,
density (specific gravity)
Chemical property – reflect how something
chemically reacts with something else; when
tested, a chemical reaction will occur if it has
that chemical property.
Minerals Properties are caused by…
The properties (characteristics) of minerals
are determined by the structure (arrangement)
and chemical composition of the particles
inside the mineral.
Diamond
Graphite
(C)
(C)
Minerals Composition
• Mineral composition refers to the ratios of
elements present in the crystal – the chemical
formula or chemical symbol.
•
•
•
•
•
Pyrite: FeS2
Quartz: SiO2
Calcite: CaCO3
Copper: Cu
Sulfur: S
Minerals: Characteristic Properties
• Color- One of the most obvious
mineral properties, but NOT the most
useful. Many minerals come in a
large variety of colors.
• Streak- The color left behind when
mineral is scraped on unglazed
porcelain (may be the same or a
different color than the crystal).
• Luster- The manner in which light
reflects off surface of a mineral metallic vs. nonmetallic (glassy,
pearly, dull, earthy, silky).
Minerals: Characteristic Properties
• Cleavage - the smooth
breakage of a mineral
along relatively weak
planes of the crystalline
structure.
• Fracture – The rouch
and irregular breakage
of a mineral (choncoidal
fracture).
Basal or platy
cleavage
Prismatic
cleavage
Cubic
cleavage
Rhombohedral
cleavage
Octahedral
cleavage
Describe the Cleavage
B
A
D
C
Minerals: Characteristic Properties
Hardness- The
scratch-resistance of a
mineral based on a
scale from 1 to 10.
Moh’s Scale of Hardness
Hardness Test Warning!
Don’t confuse a scratch with a streak. You
can’t rub a scratch off!
Minerals: Characteristic Properties
Crystal Form (or Crystal Habit)
The geometric shape of a well-formed crystal
(the growth shape if there was room to grow).
More Characteristic Properties of
Minerals
• Reactivity to acid- The chemical response of a mineral to
hydrochloric acid, causing the mineral to fizz
(effervescence).
• Double Refraction – The ability to split light rays to
produce two images.
• Magnetism- The attraction to a magnet.
• Density/Specific gravity- How heavy a mineral seems (for
its size): High, medium, or low as determined by hefting.
• Fluorescence – the ability to glow in the dark after
exposure to ultraviolet light.
• Irridescence – the ability to produce a play of colors.
HCl Test
CaCO3 + 2HCl  CaCl2 + CO2 + H2O
Wash the specimen and dry it.
Wash your hands too!
Identifying Feldspars
Alkali Series- Wavelets
Identifying Feldspars
Plagioclase Series- Striations
Non-Silicate Minerals
Some noteworthy non-silicate minerals are:
• Native elements- Composed entirely of one
element (copper, gold, diamond).
• Carbonates- Contain CO32- (calcite, CaCO3).
• Sulfates- Contain SO42- in their structures
(gypsum, CaSO4· 2H2O)
• Sulfides- Contain S2- (but no O) in their structures
(galena, PbS; pyrite FeS2)
• Oxides- Contain O2- bonded to metal atoms
(hematite, Fe2O3; magnetite, Fe3O4)
Chapter 4.2 - The Silicate Minerals
• Five minerals (out of 3000) account for
90% of the minerals in Earth's crust.
• These are:
– Quartz
– Feldspar
– Pyroxene
– Amphibole
– Mica
All contain Silicon and Oxygen!
The Silicate Minerals
• The silicate minerals all contain Si and O
covalently bonded together to form a
silicon-oxygen tetrahedron:
Silicate Mineral Structures
• The basic structure for silicate minerals is a
silicon-oxygen tetrahedron.
• Contains 1 silicon at the center, and 4 oxygen
atoms at the corners.
• Each tetrahedron is negatively charged (SiO44-).
The extra negative charge (-4) means that
positive metal ions like Mg, Ca, Fe, Al etc.
are needed for charge balance (i.e., MgSiO3).
The metal ions go in between the silicate
tetrahedra.
Different
arrangements
of the silicate
tetrahedra 
5 major,
different
silicate
structures.
Isolated Tetrahedra- No oxygen
atoms are shared between tetrahedra.
Examples: Olivine, Garnet, Topaz
Single Chain silicates- 2 oxygen
atoms on each tetrahedron are
shared.
Example: Pyroxene
Pyroxenes
Enstatite: MgSiO3
Ferrosilite: FeSiO3
Double-chain silicate- Alternating 2
and 3 oxygen atoms on each
tetrahedron are shared.
Example: Amphibole (hornblende)
Amphiboles
Hornblende:
Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)2
Sheet silicates- 3 oxygen atoms on
each tetrahedron are shared.
Examples: Biotite, Muscovite, Talc, Clays
Micas
Biotite: K(Fe,Mg)3AlSi3O10(F, OH)2
Micas
Muscovite: KAl2(AlSi3O10)(F,OH)2
Talc
(Mg,Fe)3Si4O10(OH)2
Framework silicates- All 4 oxygen
atoms on each tetrahedron are
shared.
Examples: Quartz, Feldspar
Quartz (SiO2)
(Fixed composition)
Feldspar Group Minerals
K-Feldspar: KAlSi3O8
Albite: NaAlSi3O8
Anorthite: CaAl2Si2O8
(Somewhat variable composition)
Gemstones
What properties of minerals make certain
specimens suitable for jewelry (gemstones)?
Gemstones
•
•
•
•
Attractive color/transparency.
High hardness.
Good cleavage.
Rarity.
Gemstones Have “Special” Names
Mineral name: Quartz
Gemstone name: Amethyst
Gemstones Have “Special” Names
Mineral name: Olivine
Gemstone name: Peridot
Gemstones Have “Special” Names
Mineral name: Corundum
Gemstone name: Ruby or Sapphire