PHYSICAL PROPERTIES OF MINERALS

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PHYSICAL PROPERTIES OF MINERALS
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Mineral Identification Basics

• What is a Mineral?

There is a classic definition for mineral.
Minerals must be

• Inorganic
• Occurs Naturally on Earth
• Always a Solid
• Has Definite Chemical Composition
• Crystalline Structure

Cubic Fluorite Crystal
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Mineral Identification Basics

• What is a Mineral?

Naturally Occurring

• Minerals are not synthetic or man made - they
  are produced by the natural geological processes
  working on Earth.

Tourmaline Crystal from Brazil
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Mineral Identification Basics

• What is a Mineral?

Inorganic

• Minerals are NOT produced by organic living
  processes. As a result things like pearls,
  coral, coal and amber are NOT considered
  minerals.

Barite Rose - A flower like growth of Barite
crystals.
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Mineral Identification Basics

• What is a Mineral?

Crystalline Structure
Minerals are the result of atoms joining together
through electrical bonds to produce a definite
internal structure.
Crystalline Pattern of Halite Red Sodium Green
Chlorine
Halite (salt) from Searles Lake, CA
()
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Mineral Identification Basics

• What is a Mineral?

Definite Chemical Composition

• Minerals can be expressed by a chemical
  formula. The internal order of minerals means
  that there is a definite relationship in the
  number of atoms that makes up the mineral.

Halite - NaCl For every atom of Sodium there is
an atom of Chlorine.
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Mineral Identification Basics

• PHYSICAL PROPERTIES HARDNESS

HARDNESS is defined as the resistance a mineral
has to being scratched - its scratchability.
Hardness tests are done by scratching one mineral
against another. The mineral that is scratched
is softer than the other.
Pyrite Crystals Hardness of 6.5
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Mineral Identification Basics

• PHYSICAL PROPERTIES HARDNESS

In this photo, a quartz crystal will be rubbed
across a glass plate. The result is that the
glass plate will be scratched. The quartz is
therefore harder than the glass.
Quartz is harder than glass.
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Mineral Identification Basics

• PHYSICAL PROPERTIES HARDNESS

Care must be taken on some minerals that crumble
easily. Remember that hardness is the resistance
a mineral has to being scratched - NOT how easily
it breaks apart.
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Mineral Identification Basics

• PHYSICAL PROPERTIES HARDNESS

MOHS SCALE OF MINERAL HARDNESS
1. TALC 2. GYPSUM 3. CALCITE 4. FLUORITE 5.
APATITE
6. FELDSPAR 7. QUARTZ 8. TOPAZ 9.
CORUNDUM 10. DIAMOND
OTHER MATERIALS COMMONLY USED 2.5 -
FINGERNAIL 3 - COPPER PENNY 5.5 -
GLASS 6-6.5 - STEEL
FILE
Mohs scale is a list of minerals with increasing
hardness.()
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Mineral Identification Basics

• PHYSICAL PROPERTIES CLEAVAGE

CLEAVAGE is the property of a mineral that allows
it to break repeatedly along smooth, flat
surfaces.
These GALENA cleavage fragments were produced
when the crystal was hit with a hammer. Note the
consistency of the 90o angles along the edges.
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Mineral Identification Basics

• PHYSICAL PROPERTIES CLEAVAGE

Within this crystalline pattern it is easy to see
how atoms will separate to produce cleavage with
cubic (90o) angles. ()
It is similar to tearing a piece of paper that
has perforations in it. The paper has a tendency
to tear along the perforations. They are zones
of weakness. ()
In this example the lines represent breaks
between the atoms that make up the mineral.
Cleavage is guided by the atomic structure. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES CLEAVAGE

These pictures show different cleavage angles and
the quality of cleavage.
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Mineral Identification Basics

• PHYSICAL PROPERTIES CLEAVAGE

Common salt (the mineral HALITE) has very good
cleavage in 3 directions. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES CLEAVAGE

()
Even these tiny fragments have rhombohedral
cleavage. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES FRACTURE

FRACTURE is defined as the way a mineral breaks
other than cleavage. ()
This is a piece of volcanic glass called
OBSIDIAN. Even though it is NOT a mineral, it is
shown here because it has excellent conchoidal
fracture. ()
If you try this yourself, use caution.
Conchoidal fracture in obsidian can produce
extremely sharp edges. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES FRACTURE

This Quartz crystal will be struck with a hammer
to show how that the external form of the crystal
does not repeat when broken. (The flat crystal
faces are not cleavage faces.) This is a good
example of conchoidal fracture. ()
Note the smooth curved surfaces.
()
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Mineral Identification Basics

• PHYSICAL PROPERTIES STREAK

STREAK is defined as the color of the mineral in
powder form. ()
Streak is normally obtained by rubbing a mineral
across a streak plate. This is a piece of
unglazed porcelain. The streak plate has a
hardness of around 7 and rough texture that
allows the minerals to be abraded to a powder.
This powder is the streak. ()
Hematite has a reddish brown streak. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES STREAK

Sphalerite is a dark mineral, however, it has a
light colored streak. Next to the reddish brown
streak of hematite is a light yellow streak.
This is the streak of the sphalerite. ()
Light colored streaks are often difficult to see
against the white streak plate. It is often
useful to rub your finger across the powder to
see the streak color. ()
Sphalerite has a light yellow streak. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES LUSTER

LUSTER is defined as the quality of reflected
light. Minerals have been grossly separated into
either METALLIC or NON-METALLIC lusters.
Following are some examples
Native Silver has a Metallic Luster. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES LUSTER METALLIC

The basic idea for Metallic Luster is that the
minerals look like metals. ()
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Mineral Identification Basics

• NON-METALLIC LUSTER VITREOUS

Vitreous Luster means that the mineral has a
glassy look. Normally we think of glass as
being clear, but there are many different colors
of glass and they are all very glassy looking.
Even china plates and glazed porcelain are
vitreous. Here are some examples ()
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Mineral Identification Basics

• NON METALLIC LUSTER

Miscellaneous Lusters
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Mineral Identification Basics

• PHYSICAL PROPERTIES COLOR

The COLOR of a mineral is usually the first thing
that a person notices when observing a mineral.
However, it is normally NOT the best physical
property to begin the mineral identification
process. ()
Following are some examples of color variation
within mineral species followed by minerals that
have a distinctive color ()
Various colors of CALCITE. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES COLOR

Quartz comes in a wide range of colors. It is
very easily colored by even trace amounts of
impurities. ()
Various colors of Quartz.
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Mineral Identification Basics

• INDICATIVE COLOR

Some minerals do have a certain color associated
with them. Here are some examples ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES SPECIFIC GRAVITY

The SPECIFIC GRAVITY of a mineral is a measure of
the minerals density. It is related to the
types of elements that make up the mineral and
how they are packed into the minerals atomic
structure.
Gold in Quartz
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Mineral Identification Basics

• PHYSICAL PROPERTIES TASTE

IT IS NOT RECOMMENDED THAT A TASTE TEST BE
PERFORMED ON MINERALS AS A STANDARD PROCESS.
SOME MINERALS ARE TOXIC. However, the mineral
HALITE is common salt and has a unique taste. ()
Halite cubes from Trona, CA ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES MAGNETISM

MAGNETISM is the ability of a mineral to be
attracted by a magnet. This most commonly is
associated with minerals rich in iron, usually
magnetite.
This is a piece of MAGNETITE with a magnet
adhering to it. Magnetite is a mineral that is
strongly magnetic in that a magnet will easily be
attracted to it. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES MAGNETISM

This is a sample of black sand from Lynx Creek,
Arizona. Its dark color is due to its high
concentration of magnetite. See what happens
when a magnet is place beneath the bottom right
portion of the paper. ()
This technique is used to separate out much of
the unwanted material in the search for gold in
placer deposits. ()
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Mineral Identification Basics

• PHYSICAL PROPERTIES MAGNETISM

LODESTONE is a variety of Magnetite that is
naturally a magnet. ()
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Mineral Identification Basics

• DOUBLE REFRACTION

DOUBLE REFRACTION Is a property shared by many
minerals ( but not those in the isometric crystal
system). It is produced by the separating of a
beam of light as it passes through the crystal
structure. It is best displayed in the mineral
CALCITE. This image clearly shows the double
image below the calcite.
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Mineral Identification Basics

• CHEMICAL PROPERTIES
• REACTION TO ACID

Some minerals, notably the carbonates, react to
cold dilute HCl. In this illustration a piece of
CALCITE is shown to react (fizz) after HCl is
applied.
Calcite Reacts to HCl ()
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This ends the basic introduction to the Physical
Properties of Minerals.