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The Earth’s Crust
Mineral Identification
Tuesday, May 23, 2017
Mineral Identification
What differences
can you see
between these
minerals that could
help identify them?
What properties
could be used to
identify minerals?
There are six main characteristics
that can be used to identify
minerals:
– 1. colour
– 2. crystals (the shape of)
– 3. hardness
– 4. streak
– 5. cleavage and fracture
– 6. luster
1. Colour
Colour - It's pretty
easy to tell the
colour of a mineral
and it can give a
clue to the identity
of the mineral.
However, colour
alone cannot
identify a mineral.
For example, pyrite
(fools gold) and
gold are both the
same colour.
In addition, not all
minerals are the same
colour all the time.
For example, the
mineral corundum can
occur in several
different colours due
to impurities.
Corundum is better
known as amethyst
(purple), emerald
(green), topaz
(yellow), and ruby
(red). In its pure form,
corundum is white.
2. Crystals
Crystal shape –
Minerals sometimes
occur as crystals. A
crystal occurs
naturally and has
straight edges, flat
sides, and regular
angles.
Each mineral forms a
specific shape of
crystal so it can be
used for identification
purposes.
3. Hardness
Hardness – the
hardness of a
mineral can be
measured and
compared to other
minerals using the
Moh’s Hardness
Scale.
The scale goes from
one (the softest) to
10 (the hardest) and
ranks minerals on
their “scratchability”
Mineral
Mineral
Hardness
Hardness of
Common Items
talc
1 (softest)
Soft pencil point
(1.5)
gypsum
2
Fingernail (2.5)
calcite
3
Copper penny (3.5)
fluorite
4
Iron nail (4.5)
apatite
5
Glass (5.5)
feldspar
6
Steel file (6.5)
quartz
7
Streak plate (7)
topaz
8
Sandpaper (7.5)
corundum
9
Emery paper (9.0)
diamond
10 (hardest)
4. Streak
Streak – the colour a
mineral leaves behind
when it is rubbed on
a hard surface
(usually a streak
plate)
Often the colour a
mineral leaves behind
is different from the
colour of the mineral.
5. Cleavage and Fracture
Cleavage and
Fracture –
Describes how a
mineral breaks
apart
The way a mineral
breaks apart can be a
clue to its identity.
If it breaks along
smooth, flat surfaces,
or planes, it is said to
have cleavage.
e.g. calcite or mica Mica can be pulled
apart into thin, flat,
sheets and Halite
forms flat edges
when broken.
If it breaks with
rough or jagged
edges, it is said
to have fracture.
E.g. obsidian
Obsidian
fractures when
broken apart
leaving rough,
jagged edges.
6. Lustre
Lustre – the ability of a mineral
to reflect light
The "shininess," or lustre of a
mineral depends on how light is
reflected from its surface.
The surface of a
mineral can
reflect light in
many different
ways including:
1. Metallic
Lustre - the
mineral reflects
light like a
polished piece
of metal.
2. Vitreous
Lustre (Glassy) the mineral
reflects light
like a piece of
glass when it is
tilted from side
to side.
3. Pearly Lustrethe mineral
reflects light
like a pearl.
4. Dull Lustre the mineral
scatters the
light and will not
appear shiny at
all.