Download Properties of Minerals

Properties of Minerals
What are minerals?
• There are over 3000 minerals.
• Roughly 100 common minerals
• A mineral is a naturally occurring,
inorganic solid that has a crystal structure
and definite chemical composition.
5 Characteristics of Minerals
• Naturally Occurring
• Inorganic
• Solid
• Crystal Structure
• Definite Chemical Composition
Naturally Occurring
• Formed by geological processes not man.
• Ex: Copper is a mineral but steel is not
because it is made by man.
Inorganic
• A mineral cannot be made from a material
that was once a part of a living organism.
• Ex: Oil and coal form naturally in the
Earth’s crust, but form from the remains of
animals and plants from millions of years
ago.
Solid
• A mineral has to be solid with a definite
shape and volume.
• In a solid the molecules are packed tightly
so they cannot flow freely, so the object
keeps it’s shape.
Crystal Structure
• A mineral is made up of a pattern that continually
repeats
• The repeating pattern of a mineral’s particles forms a
solid called a CRYSTAL.
• Sometimes you are able to see the crystal with the
naked eye other times you must use a microscope.
• Opal is considered a mineral even though their particles
are not arranged in a crystal structure.
Definite Chemical Composition
• A mineral has a definite chemical composition.
• Meaning: Minerals contain certain elements in
definite proportions.
• Almost all minerals are compounds: made of 2
or more different elements bonded together.
• Some minerals are made of one element:
Examples are gold, silver, and copper.
Element, Compound, Mixture
• Mixture: is a substance composed of two or
more substances that re mixed together but not
chemically.
• Each substance in a mixture keeps their separate properties.
Example: Salt Water
• Element: a substance composed of one type of
atom. Each element has unique chemical and
physical properties.
• Compound: is a substance composed
of two or more elements where the
elements no longer have distinct
properties.
• Each compound has it’s own
properties that differ from the
properties of each element.
Identifying Minerals
• Gold Rush: COLOR ALONE WILL NOT WORK!
• Each mineral has its own unique physical properties
that can be used to identify it.
• The following characteristics can be used to identify
minerals:
– Hardness
Color
Streak
– Luster
Density
Crystal Systems
– Cleavage/Fracture Special Properties
Color
• Very simply what is the color of the
mineral.
• This can be easily seen however color can
only be used to identify a few minerals
because only a few minerals have their
own characteristic color.
• For example azurite is always blue.
• Some minerals like quartz are found in
several colors.
Streak
• The streak of a mineral is the color of its powder.
• You can determine this by rubbing a mineral
against a piece of unglazed tile called a streak
plate.
• The color of a mineral may vary, but its streak
will not.
– Pyrite: Gold color
– Gold: Gold color
Greenish black streak
Yellow streak
Luster
• This term is used to describe how a mineral
reflects light from its surface.
• Minerals containing metals are often shiny.
• Ex: Galena: Metallic Luster
• Some of the terms used to describe a nonmetallic luster in minerals:
– Glassy, earthy, waxy, pearly, silky.
Hardness
• How hard a mineral is an excellent tool for
identifying the mineral.
• MOHS HARDNESS SCALE was invented
to test and compare the hardness of
different minerals.
• The scale ranks 10 minerals from softest
to hardest.
Hardness (continued)
• A mineral can scratch any mineral softer
than itself and it will be scratched by any
mineral harder than itself.
Mohs Hardness Scale
Mohs Mineral Hardness
Talc
Gypsum
Calcite
Fluorite
Apatite
Orthoclase
Quartz
Topaz
Corundum
Diamond
1
1.5
2
2.5
3
4
5
5.5
6
6.5
7
8
9
10
Example
Fingernail
Copper coin
Other Mineral
Graphite
“
“
Steel nail
Glass plate
Steel file
Garnet
Density
• Each mineral has a characteristic Density.
• Density = Mass / Volume (remember the heart)
Crystal Systems
• Crystals of each mineral grow atom by
atom to form that mineral’s particular
crystal structure.
• There are 6 groups/ mineral structures:
• Cubic
• Monoclinic
Hexagonal
Triclinic
Tetragonal
Orthorhombic
Cleavage
• A mineral that splits easily along flat surfaces
has this property.
• Cleavage is determined by the arrangement of
atoms inside the mineral.
• Depending on the arrangement minerals may
split more easily in one direction than another.
Fracture
• Fracture describes how a mineral looks
when it breaks apart in an irregular way.
Special Properties
• Some minerals have special properties
such as FLUORESCENCE.
• These minerals will glow under fluorescent
light.
• Some minerals are magnetic.
Ex: Lodestone
Special Properties
• Calcite fizzes and gives off Carbon dioxide
when you drop acid on it.
• Quartz has electrical properties:
– If pressure is applied to these crystals a small
electrical current is produced. Because of
these properties, quartz crystals are used in
watches, microphones, etc.