2.2 notes a mineral is identified by its properties
TRANSCRIPT
2.2 NOTES
A Mineral is Identified by its Properties
A MINERAL IS IDENTIFIED BY ITS PROPERTIES
The pictures to the right are all of the mineral Fluorite.
The pieces are different in color, size, and crystal shape, but they are all still Fluorite!
How is this possible?
A MINERAL IS IDENTIFIED BY ITS PROPERTIES
As you can see, fluorite occurs in many colors, even colorless forms.
Its crystals can be well formed or poorly formed, smooth, or rough.
A MINERAL IS IDENTIFIED BY ITS PROPERTIES
If you came across fluorite while hiking, would you know what it was just by looking at it? Probably not.
In this section we will learn how you could identify it.
A MINERAL’S APPEARANCE HELPS IDENTIFY IT
To identify a mineral, you need to observe its properties-characteristic features that identify it.
COLOR AND STREAK
Most minerals have a limited color range.
COLOR AND STREAK
3 main factors cause minerals to be slightly different colors…
COLOR AND STREAK
1. A mineral may get its color from tiny amounts of an element that is not part of its normal chemical makeup.
COLOR AND STREAK
Example: Pure quartz is clear and colorless.
Tiny amounts of iron turn quartz purple. This is called amethyst.
COLOR AND STREAK
2. A mineral’s color can change when it is at or near Earth’s surface and is in contact with the atmosphere or water.
COLOR AND STREAK
3. Mineral crystals might have different shapes that change their color. Example: Hematite with small crystals looks dull.
Hematite with large crystals looks shiny.
COLOR AND STREAK
Some minerals have a different color when they are ground into a fine powder than when they are left whole.
COLOR AND STREAK
Streak is the color left behind when a mineral is scraped across a surface.
COLOR AND STREAK
Scientists use a piece of porcelain, called a streak plate, to help identify minerals
COLOR AND STREAK
Streak is a better clue to a mineral’s identity than surface color.
COLOR AND STREAK
All samples of the same mineral have the same streak.
LUSTER
Luster is the way in which light reflects from a mineral’s surface.
LUSTER
Metallic luster makes a mineral look as if it were made of metal. For example, Pyrite (Fool’s Gold) has a metallic luster.
LUSTER
Nonmetallic luster gives minerals a shiny look, but they do not appear to be made of metal.
THE WAY A MINERAL BREAKS HELPS IDENTIFY IT
Each kind of mineral always breaks in the same way.
THE WAY A MINERAL BREAKS HELPS IDENTIFY IT
Calcite breaks into tilted blocks.
Mica splits into thin, flat sheets.
CLEAVAGE
Cleavage is the tendency of a mineral to break along flat surfaces.
CLEAVAGE
The way in which a mineral breaks depends on how its atoms are bonded.
Minerals that have cleavage have weak bonds in the direction that the mineral breaks
FRACTURE
Fracture is the tendency of a mineral to break into irregular pieces.
FRACTURE
Minerals that have fracture have bonds that are equal in all directions.
This means the mineral will not break along flat surfaces. Example: Quartz breaks by
fracturing.
A MINERAL’S DENSITY AND HARDNESS HELP IDENTIFY IT
A tennis ball is not as heavy or as hard as a baseball.
You would be able to tell the two apart even with your eyes closed.
Minerals can be identified in the same way.
DENSITY
What weighs more, a pound of bricks or a pound of feathers?
DENSITY
What takes up more room, a pound of bricks or a pound of feathers?
DENSITY
The bricks are more dense; they have more density!
DENSITY
Density is the amount of mass in a given volume of a substance.
DENSITY
Example: 1 cm3 of pyrite has a mass of 5.1 grams.
Its density is 5.1 g/cm3
DENSITY
Examining the density of minerals is a helpful way of identifying them.
Real gold is far more dense than pyrite (fool’s gold).
HARDNESS
A mineral’s hardness is its resistance to being scratched.
HARDNESS
The Mohs scale is often used to describe a mineral’s hardness.
On the Mohs scale, Talc is the softest with a value of 1 and Diamond is the hardest with a value of 10.
HARDNESS
You can test the hardness of various minerals by the items they are or are not able to scratch.
SOME MINERALS HAVE SPECIAL PROPERTIES
Some, but not all, minerals have special properties that help to identify them.
SOME MINERALS HAVE SPECIAL PROPERTIES
Minerals in the carbonate group react with acid.
SOME MINERALS HAVE SPECIAL PROPERTIES
Fluorescent minerals glow when they are exposed to UV light.
REVIEW
1. How is it possible for two different minerals to have the same chemical composition?
A. They have different chemical structures.
B. One is formed only by organisms.
C. Only one is a rock-forming mineral.
D.They have different appearances.
REVIEW
2. Which of the following is the least reliable clue to a mineral’s identity?
A.Color
B.Density
C.Hardness
D.Luster
REVIEW
3. Many properties of a mineral are related to the
A. Number of elements of which it is made.
B. Other types of minerals present as it formed.
C. Strength of bonds between its atoms
D.Speed at which it formed.