Download What is a Mineral?

What is a Mineral?
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Naturally occurring
Inorganic
Solid
Definite crystalline structure
Definite chemical composition
Mineral characteristics
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Naturally formed
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No substance created in a lab can be a
mineral.
examples: plastic, steel, sugar, paper
•
Inorganic
– Not living
•
Solid
– Liquids and gases are not minerals.
examples: water, petroleum, lava, oxygen
Mineral characteristics
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Characteristic crystalline structure
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must have an ordered arrangement of atoms
displays repetitive geometric patterns in 3-D
glass not a mineral (no internal crystalline structure)
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Definite chemical composition
– must have consistent chemical formula
examples: gold (Au), quartz (SiO2), orthoclase (KAlSi3O8)
basalt (like many other rocks) contains variable ratios of different minerals;
thus, has no consistent formula
Mineral Structure
Crystals: solids with atoms arranged
in orderly, repeating patterns.
Some crystals form from magma, hot
melted rock below the Earth’s surface.
When magma cools slowly, crystals are
large.
When magma cools quickly, crystals
are small.
Crystals can form from solutions as
water evaporates or if too much of a
substance is dissolved in water.
GRANITE ROCK
Minerals
are the
building
blocks of
rocks
Mineral Structure
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Contain one or more elements
which are made of atoms
Most made of compounds of
several elements (Quartz SiO2)
Mineral composed of one element
called native element (Gold Au)
Other minerals broken into groups
based on chemical composition
Types of atoms/molecules that
make up mineral and arrangement
determine shape of mineral
Identifying Minerals
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Six main properties:
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Color
Luster
Streak
Cleavage or Fracture
Hardness
Density/specific gravity
Special Properties
Identifying Minerals
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Color:
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Most obvious, but often misleading
Many minerals have same/similar color
Different colors may result from impurities
Example:
Quartz
Discuss the following!
Can you remember the
definition of a mineral?
How many properties
can you remember?
Why isn’t color a very
good property to
identify most minerals?
Identifying Minerals
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Luster:
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Metallic
example:
Galena
How a mineral surface reflects light (shines)
Two major types:
 Metallic luster
 Non-metallic luster
Non-metallic
example:
Orthoclase
There are several terms used to
describe nonmetallic luster.
Examples could be vitreous,
like the quartz on the left, or
pearly, like the gypsum on the
right.
Other terms that might be used
include greasy, dull, and earthy.
Can you tell which of these has an
earthy luster and which has a
vitreous luster?
Vitreous
Earth
Identifying Minerals
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Streak:
Streak – color of a mineral in powdered form
(used for metallic minerals)
Obtained by scratching a
mineral on a piece of unglazed
porcelain.
Example:
Hematite
The streak is often not the
same color as the mineral.
A minerals color may vary, but
the streak rarely will!
Identifying Minerals
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Cleavage vs. Fracture:
The way a mineral breaks
– Cleavage: tendency of a mineral to break
along planes of weakness (smooth)
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– Minerals that do not exhibit cleavage are said
to fracture (uneven)
Minerals with cleavage break along
smooth, flat surfaces.
Physical Properties of Minerals
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Cleavage (1 direction):
Example: mica
Physical Properties of Minerals
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Cleavage (2 directions):
orthoclase
amphibole
Physical Properties of Minerals
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Cleavage (3 directions):
halite
calcite
Physical Properties of Minerals
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Cleavage (4 directions):
fluorite
Physical Properties of Minerals
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Fracture:
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minerals that do not exhibit cleavage are said to
fracture
minerals with fracture break with uneven, rough,
or jagged surfaces
Identifying Minerals
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Hardness:
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How easy it is to scratch a mineral
Mohs Scale of Hardness
 relative scale
 consists of 10 minerals, ranked 1 (softest)
to 10 (hardest)
Mohs Scale of Hardness
Hardest (10) – Diamond
Softest (1) – Talc
Common objects:
- Fingernail (2.5)
- Copper penny (3.5)
- Wire nail (4.5)
- Glass (5.5)
- Streak plate (6.5)
Identifying Minerals
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Specific gravity:
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weight of a mineral divided by weight of an
equal volume of water
metallic minerals tend to have higher specific
gravity than non-metallic minerals
Galena
SG=7.5
Quartz
SG=2.67
Specific Gravity/Density
=
Density – how much matter is in
something (Density=mass/volume)