What is a Mineral
Naturally Occurring
Inorganic
Homogenous Solid
Definite Chemical Composition
Internal arrangement of atoms
Properties of Minerals
Each mineral can be
identified by its
unique properties.
For example:
•Galena can be identified by its
very high density and its cubic
cleavage.
•Quartz can be identified by
its luster, lack of cleavage
and hardness.
•
•Mica
can be identified by its
cleavage.
•Sulfur can be identified by its
color.
•Magnetite is magnetic.
•Calcite fizzes when
hydrochloric acid is dropped
onto it.
Why do minerals have
certain properties?
The properties of each
mineral are determined by
its internal arrangement of
atoms.
Do Now
1. Why do humans use minerals?
2. How many minerals can be found on
Earth?
3. 90% of all rocks are made of up
_____common minerals?(how many)
4. What is a mineral?
Major Properties
Color- what it looks like to our eyes
Luster- how the surface reflects light
Streak- color of the minerals powder
Hardness- how resistant to scratching
Cleavage- breaking along surfaces
Density- packing of atoms
Crystal Shape- angles between sides
ColorSome minerals are easily
identified by their color.
Many minerals come in a wide
variety of similar colors so it is
only occasionally useful.
Sulfur
Sulfur can
always be
identified by its
bright yellow
color.
Pyrite
Pyrite
can be
identified
by its
brass
yellow
color.
Luster
Luster is the way light is reflected from a
freshly broken surface of the mineral.
Metallic- metals do not let any light
penetrate. Therefore, they reflect all the
light hitting their surfaces.
Nonmetallic- nonmetals allow some
light to penetrate so they will appear
very different from metals.
Metallic Luster
Galena
has a
metallic
luster.
Nonmetallic Luster
Calcite
has a
nonmetallic
luster.
Hardness
Hardness is the resistance to being
scratched.
Hardness is a measure of how
tightly the atoms in a mineral are
bound together.
The test for hardness is to scratch
two objects against each other.
Hardness
If one object scratches another it is
harder than it.
Friedrich Mohs created a scale of
hardness a called the Mohs scale.
Talc is softest (1), diamond is
hardest, (10).
Mohs’ Hardness Scale
1-2.5
Fingernail scratches mineral
2.5-3.5
Fingernail does not scratch mineral,
mineral does not scratch penny.
3.5–4.5
Mineral Scratches penny, Nail
scratches mineral.
4.5-5.5
Nail does not scratch mineral,
Mineral does not scratch glass.
5.5-6.5
Mineral scratches glass, file scratches
mineral.
6.5+
File does not scratch mineral.
Cleavage- from latin (to cut or cleave)
Cleavage is the tendency to break
along lines of weakness.
If a mineral breaks along flat
surfaces it is said to have cleavage
planes.
These surfaces may or may not be
parallel to the planes of the
crystals.
Cleavage- parallel to the surface
Mica has perfect cleavage in one
direction, parallel to the crystal faces.
Cleavage- parallel to the surface
Halite (rock salt)- Natural crystals form cubes.
Cleavage- parallel to the surface
Halite -breaks into cubes.
Diamond
Concoidal Fracture- curved, not
parallel to the crystal surfaces.
Obsidian (volcanic
glass) breaks along
curves. This is
called concoidal
fracture.
Even though quartz has crystal faces it only
has concoidal fracture. It never breaks
parallel to the surface. (No cleavage.)
Streak
The streak is the color of a
mineral’s powder.
A streak is made by rubbing the
mineral over an unglazed ceramic
tile. If the mineral is not as hard as
the tile some of the mineral will
rub off.
Streak
The color of the powder can be
easily seen against the white tile.
If the mineral is harder there will
be a white streak.
Some metallic minerals have a
different color streak than the color
of the mineral.
Streak
To make the streak test just
carefully rub the sample on the
streak plate.
Streak is very reliable, any mineral
always has the same color streak.
Streak
Hematite
always has a
red streak, no
matter what
color the
sample of
hematite is.
Crystal Faces
If a mineral is allowed to grow
without bumping into anything else
it will grow in very specific ways
that represent its basic internal
arrangement of atoms.
Crystals of Galena
Galena crystals are cubes because the
atoms arrange themselves that way.
Crystal Faces
Crystal faces meet at specific
angles for each mineral. These
angles may be used to identify the
mineral but can only be used for
crystal faces, which are rare.
Density and Specific Gravity
Density is a measure of how tightly
packed a substance’s atoms are.
Specific gravity is the ratio of the density
of a substance to the density of water.
•Water = 1 gram/cm³.
•Galena = 7.5 gram/cm³.
•Galena has a specific gravity of 7.5.
Density
Density is a derived unit that is a
comparison of the mass of an
object to its volume.
D= mass/volume
The formula for density is found
on the front page of the ESRT
Here’s a trick!
Cover the
unit you are
trying to
calculate
and the
formula is
what is left.
The Law of Density
if matter is less dense than
the matter surrounding it will
rise until it reaches a density
that is equal to its own
density.
Substances that are less dense
will float.
 Substances that are the same
density can stay suspended.
Substances that are more dense
will sink.
The density of a substance
does not change when broken. All
the pieces of a broken substance
remain the same unless the
temperature changes.
Air is heated it
expands.
Its volume
increases
therefore the
density
decreases.
Water is special!
Water has a density of 1g/cm at
3.98EC (front cover ESRT)
Water is most dense at 4°C. Ice is
less dense therefore it floats.
Most objects are more dense as a
solid except water.
Density and Specific Gravity
•Most rocks have a specific gravity of
2.5 to 3.5. That means their density is
2.5 to 3.5 grams/cm³.
•Lead is 12.
•Gold is 19. Gold is the most dense
common substance.
Special Properties
•Magnetism- magnetite attracts
magnets, strong magnetite attracts
iron.
•Double refraction- clear calcite will
transmit two images of an object.
•Acid- calcite will react to HCl.
•Flourescence- some minerals glow in
UV light.