Minerals
How do we use Earth Materials?
• Earth Materials: minerals, rocks, and mineral
resources (95% to 100% of objects you use)
What is a mineral?
• Mineral: a naturally occurring, inorganic,
crystalline solid that has a definite chemical
composition.
1. Naturally Occurring: a mineral must be formed by
nature and not made by people.
What is a mineral?
2. Inorganic: a mineral CANNOT form from
materials that were once part of a living thing.
What is a mineral?
3. Crystalline solid: a mineral is always a solid, with
its own unique crystal structure.
What is a mineral?
4. Definite Chemical Composition: a mineral always
contains certain elements in definite proportions.
Quartz
Gold
Mineral or NOT?
• Rock salt
–AKA Halite
–NaCl
Mineral or NOT?
• Beach sand
–AKA tiny pieces of Quartz
–SiO2
–Crystal shape is a pyramid
Mineral or NOT?
• Snow
– Occurs naturally
Mineral or NOT?
• An ice cube
How are Minerals Related to Rocks?
• A rock is any naturally formed solid that is part of
Earth or any other celestial object.
– Organic or glassy rocks are NOT minerals.
How are Minerals Related to Rocks?
• There is only a
small number of
minerals
commonly
found in rocks.
Mineral Crystal Structure
• A mineral’s atomic arrangement is responsible for
many of its chemical and physical properties.
Silicate Minerals
• What two elements, by mass, make up the
greatest percentage of the Earth’s crust?
These two elements combine to form
compounds called silicates.
The mineral Quartz is a type of
silicate (SiO4)
They (Silica and Oxygen) combine in a
specific structure called a:
Silicon-oxygen tetrahedron.
Draw this structure below.
O
Si
O
O
O
Mineral Formation
Minerals can form in TWO ways:
1. Crystallization of molten material
2. Crystallization of materials dissolved in water.
Salt on a stone of
the Dead Sea, Israel
Massive beams of selenite dwarf human explorers in Mexico's Cave of Crystals, deep below the
Chihuahuan Desert. Formed over millennia, these crystals are among the largest yet discovered on Earth
Mineral Identification
• Each mineral has unique properties that can be
used to identify it.
1. Color: the easiest test to do on a mineral, but the
least reliable.
Rose Quartz
Amethyst
Citrine
Quartz
Halite
Calcite
Corundum
Mineral Identification
2. Streak: the color of the powdered mineral
• Obtained by rubbing the unknown mineral on a
streak plate (porcelain tile).
The mineral
Hematite ALWAYS
has a red streak
One way to tell Fool’s Gold apart from
real Gold is by their STREAK.
Real gold has a
golden streak
Pyrite has a
black or dark
green streak
Mineral Identification
3. Luster: The shine from an unweathered mineral’s
surface
– Metallic – shines like a polished piece of metal.
– Non-metallic – does NOT shine like a metal.
Metallic luster in
Pyrite
Glassy luster in
Quartz
Metallic luster in
Galena
Pearly luster in
Muscovite
Earthy luster in
Hematite
Mineral Identification
4. Hardness: a mineral’s
resistance to scratching
The hardness of some common items:
•Fingernail – 2.5
•A Penny – 3.5
•Glass – 5.5
•A Streak Plate – 6.5
Mineral Identification
5. Specific Gravity: the density of a mineral
compared to the density of water.
The mineral Galena has a high
specific gravity
Mineral Identification
6. Cleavage: the tendency of a mineral to break
along the zones of weakness
• Minerals can have one, two, or several cleavage planes
Mica has ONE
cleavage plane
Feldspar has TWO
cleavage planes
Halite (salt) has
THREE cleavage
planes
Mineral Identification
7. Fracture: a mineral may break along uneven
surfaces.
• Mineral has no preferred zones of weakness.
Splintery fracture in
Hornblende
Conchoidal fracture
in Quartz
Mineral Identification
8. Crystal Structure: orderly arrangement of the
atoms in the mineral
• The geometric shape of a mineral can reflect its
crystal structure.
Herkimer Diamonds are quartz
crystals that have a unique
18-sided geometric shape.
Other Ways to Identify Minerals
• Acid – Calcite will fizz in weak hydrochloric acid (HCl)
• Magnetism – Magnetite will pick up paper clips / staples.
• Taste – Halite is rock salt and will taste salty.
• Fluorescence – some minerals (mostly forms of calcite)
will glow in fluorescent colors under a black (UV) light.
• Double refraction – some clear forms of calcite will make
a double image of words.
Fluorescence of Minerals
Double Refraction