Mineral Identification Tests

How to figure out what your “rock” is…

What is a mineral?

• It must have the five following characteristics:

D-I-S-C-O– Definite chemical composition– Inorganic (from non-living sources)– Solid– Crystal structure– Occurs naturally

“The Tests”

• Color• Streak• Luster

• Cleavage and Fracture• Density• Hardness

• Special properties

Color

• The chemical composition of a mineral can affect its color

• Impurities can create a variety of colors even in the same mineral

• Probably the most UN-reliable test there is

• Look at minerals under sunlight if at all possible

All of these samples are fluorite.

Streak

• The color of the powder left created by rubbing a mineral on a white porcelain streak plate (you can also use a black plate, if available, to show a white streak)

• Some minerals show a different streak than the color that they appear

Luster• The way the surface of a

mineral reflects light• This can be:– Metallic (looks like a

metal, or rusty)– Pearly– Vitreous (glassy)– Greasy (oily)– Silky

metallic

submetallic

pearly

glassy

dullearthy adamantine

resinous

Cleavage and Fracture• How a mineral breaks or

fractures along flat planes• If it always breaks in a

certain way, it is said to have “perfect” cleavage

• If it breaks in a number of planes, it is considered to have good cleavage

• If a mineral breaks unevenly or in weird shapes (also called splintering)

• This is determined by crystal structure

• Quartz has equal fracture all around

Carbonite Rose Quartz

Volume by Water Displacement1. Take a KNOWN amount of water

(less than full) in a graduated cylinder

2. Write down how much water is in the cylinder at the start.

3. Put your irregularly shaped object in the cylinder carefully (don’t splash).

4. Record the “new” amount of water in the graduated cylinder.

5. Subtract your starting amount from the final amount. This gives you the volume of the object.

Volume by Formula (not used as much in rocks…unless you find a perfect cube)

• Length times width times height• Would work really well for a tissue box

Density• Mass (kinda like weight) per unit of volume• D= m/v• Some atoms have more mass than others• Some crystal structures are more tightly

packed into a space• Can be done by water displacement and mass

or calculations of volume and mass• REALLY good for determining what you have

Hardness

• A mineral’s ability to resist scratching• This is where the Mohs Hardness Scale (or Mohs scale)

comes into play (p. 89 in textbook)– This scale compares the hardness of minerals to one another– Talc is the softest (1)– Diamond is the hardest (10)– Fingernail 2.5– Penny 3.5– Iron Nail 4.5– Glass 5.5

Special Properties• Conductivity• Acid test• Magnetism• Fluorescence

• Crystal structure (sort of like cleavage/fracture)

Conductivity

• Will a mineral allow the transfer of energy through it

• This also may tell how much metal there is in the mineral

Magnetism

• If you hold the mineral loosely and it is pulled towards a magnet

Acid test

• Does it form carbon dioxide bubbles when exposed to acid (usually a dilute hydrochloric acid is used)

Fluorescence

• If exposed to ultraviolet light the mineral may change color (or just look WAY cool!)

Crystal Structure

• The arrangement of the atoms or molecules that make up the mineral