PHYSICAL SCIENCE 120
PHYSICAL PROPERTIES OF
MINERALS
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(*)
TABLE OF CONTENTS
Physical Science 120 students are
Mineral Definition……………….……Slide 3
Hardness……………………………………..8
Cleavage……………………………….…...12
Fracture……………………………..…..….19
Streak………………………………………21
Luster…………………………..……….….23
Color……………………………………….28
Specific Gravity…………………………....31
Taste……………………………………….48
Magnetism…………………………………49
Double Refraction…………………………53
Reaction to HCl (acid)…………………….54
Diaphaneity………………………………..56
Crystals………………………………….…60
Isometric……………………………….…..62
Hexagonal……………………………….…66
Tetragonal………………………………….70
Orthorhombic…………………………..…..74
Monoclinic………………………………....79
Triclinic…………………………………….82
Resources…………………………………..85
required to do pages 1 – 54.
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Mineral Identification Basics
• What is a Mineral?
There is a classic four part
definition for mineral.
Minerals must be: (*)
Naturally occurring (*)
Inorganic (*)
Possess a definite crystalline
structure (*)
Have a definite chemical
composition (*)
Cubic Fluorite Crystal
Mineral Identification Basics
• What is a Mineral?
Naturally Occurring (*)
Tourmaline Crystal from Brazil
Minerals are not synthetic - they are produced
by the natural geological processes working on
Earth. For example, steel, brass, bronze and
aluminum are not considered minerals in that
they are not found in nature. (*)
Technically speaking, synthetic gemstones are
not considered minerals. This area of mineralogy
has a hazy boundary in that synthetic stones are
in every way the same as the natural stones. But
because they are produced in laboratories, they
do not meet the classic definition of a mineral. (*)
Also note that many synthetic gemstones are
“doped” with a fluorescent dye to distinguish
them from natural stone. (*)
Mineral Identification Basics
• What is a Mineral?
Inorganic (*)
Minerals are NOT produced by organic
processes. As a result things like pearls, coral, coal
and amber are not considered minerals.
Also included in this
“NOT a Mineral List” are
Barite Rose - A flower like growth
of Barite crystals.
teeth, bones, sea shells and
even kidney stones. (*)
Mineral Identification Basics
• What is a Mineral?
Internal Structure
Minerals are the result of atoms joining
together through electrical bonds to produce a
definite internal structure. (*)
It is the nature of the atoms and the strength of
the chemical bonds that determine many of the
minerals’ physical and chemical properties. (*)
Crystalline Pattern of Halite
Red = Sodium
Halite (salt) from Searles Lake, CA
Green = Chlorine
(*)
Mineral Identification Basics
• What is a Mineral?
Definite Chemical Composition
(*)
Halite - NaCl
For every atom of Sodium there is
an atom of Chlorine.
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. (*)
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 (*)
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.
HINT: In doing a hardness test try to pick a
smooth or flat surface on the mineral to be
scratched. Try to pick a point or a sharp edge on
the mineral that you think will do the scratching.
Glass is usually a good place to start because it is in
the middle of the hardness table, it has a flat,
smooth surface and it is easily obtained. (*)
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. The physical property
related to the ease in which a mineral breaks is tenacity. (*)
Also be sure to determine the hardness of a mineral on a fresh
surface whenever possible. Some minerals have a tendency to
oxidize or corrode. These surface deposits usually have a different
hardness than the fresh mineral. (*)
Mineral Identification Basics
• PHYSICAL PROPERTIES HARDNESS
MOH’S SCALE OF MINERAL HARDNESS
1. TALC
6. FELDSPAR
2. GYPSUM
3. CALCITE
4. FLUORITE
5. APATITE (*)
7. QUARTZ
8. TOPAZ
9. CORUNDUM
10. DIAMOND (*)
OTHER MATERIALS COMMONLY USED:
Moh’s scale is a list of minerals with increasing hardness.(*)
2.5 - FINGERNAIL
3 - COPPER PENNY
5.5 - GLASS
6-6.5 - STEEL FILE
(*)
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. (*)
These are FLUORITE cleavage
fragments. (*)
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. (*)
Mineral Identification Basics
• PHYSICAL PROPERTIES CLEAVAGE
These pictures show different cleavage angles and the quality of cleavage.
Fluorite has cleavage in four
directions. (*)
Mica
A thin
has
sheet
perfect
of Muscovite
cleavage inseen
ONE
on
direction.
edge. (*)
Mineral Identification Basics
• PHYSICAL PROPERTIES CLEAVAGE
Common salt (the mineral HALITE) has very good cleavage in 3 directions. (*)
These 3 directions of cleavage are
mutually perpendicular resulting in
cubic cleavage. (*)
Mineral Identification Basics
• PHYSICAL PROPERTIES CLEAVAGE
Rhombohedral
Cleavage - 3 directions
CALCITE
Even these tiny fragments have rhombohedral cleavage. (*)
(*)
Mineral Identification Basics
• PHYSICAL PROPERTIES CLEAVAGE
Blocky Cleavage
2 directions
Orthoclase feldspar has good
cleavage in 2 directions.
Note that the faces in the circle are at
The
blocky
appearance
of this specimen
is
different
levels.
By adjusting
the lighting,
aall
hint
it has cleavage.
clue that
of that
the parallel
faces willThe
reflect
the
specimen has This
cleavage
is the
that
simultaneously.
results
in afact
flash
of
numerous faces will reflect light at the
light from all the parallel faces. (*)
same time. Each face is parallel and light
will reflect of each face producing a flash
Orthoclase Feldspar (*)
of light. (*)
Mineral Identification Basics
• PHYSICAL PROPERTIES CLEAVAGE
TALC has micaceous cleavage.
That is to say that it cleaves like
mica (1 perfect direction) but, in
talc the crystals are so small that
they cannot easily be seen.
Instead the effect is that the talc
“feels soapy”. The second picture
shows some of the talc that has
cleaved onto the fingers. (*)
(*)
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. (*)
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. (*)
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 on Streak Plate
Hematite has a reddish brown streak. (*)
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. (*)
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.
(*)
Mineral Identification Basics
• PHYSICAL PROPERTIES LUSTER METALLIC
Stibnite
Galena
The basic idea for Metallic Luster is that the minerals look like metals. (*)
Pyrite (*)
Marcasite
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: (*)
Olivine - Peridot
Spinel
Wulfenite
Quartz (*)
Mineral Identification Basics
• NON METALLIC LUSTER
Miscellaneous Lusters
Asbestos - Silky
Apophyllite – Pearly (*)
Graphite has a greasy or submetallic luster
and easily marks paper. (*)
Limonite - Dull or Earthy
Sphalerite - Resinous
Mineral Identification Basics
• PHYSICAL PROPERTIES LUSTER
The moral to this
story is to look at a
fresh surface
whenever
possible.(*)
This piece of Native Copper is
severely weathered. It does not
look metallic. (*)
This is the same piece but the left
side has been buffed with a steel
brush. Note the bright metallic
luster. (*)
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. (*)