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On the previous Sci-ber text page, you learned that rocks are made of minerals. Now you get to learn more about the different minerals which are found on Earth.

These observable properties are: color, hardness, luster, streak cleavage, magnetism, and specific gravity (density).

 

Color:

The color of a mineral can be useful in identifying it. Some minerals are red such as those that contain iron. Some are black, white or gray. Look at the picture of sulfur below. It is always bright yellow.

Sulfur

 

Hardness:

Some minerals are harder than others. Geologists have arranged them in order of hardness from soft to hard, based on ten common minerals. This scale, called Moh’s Hardness Scale is used to identify many minerals.

Moh’s Hardness Scale

Hardness
Mineral
Description
1
Talc Scratched easily by fingernail.
2
Gypsum Scratched by fingernail.
3
Calcite Scratched by penny.
4
Flourite Scratched easily by steel knife or nail.
5
Apatite Scratched by steel knife or nail.
6
Feldspar Scratches glass.
7
Quartz Scratches steel.
8
Topaz Scratches quartz.
9
Corundum Scratches topaz.
10
Diamond Hardest mineral
 

Streak:

Streak is the color of the powder of a mineral. The color of the streak may be different from the color of the mineral. (See the picture of hematite below) To test a mineral’s streak, rub it on an unglazed porcelain tile. The color left on the tile is its streak.

 

Cleavage/Fracture:

Cleavage and fracture refer to the way a mineral breaks. Many minerals tend to break along specific planes leaving flat surfaces; this is called cleavage. Look at the picture of calcite below and you can see the flat planes along which it broke. Other minerals break in irregular patterns; this is called fracture. Notice how differently the sulfur broke compared to the calcite. When a mineral cleaves, the angle between the planes helps us identify the mineral.

 

Magnetism:

If a mineral is magnetic it attracts iron (see the picture of magnetite below). Magnetic minerals are not extremely common so once you find one they are pretty easy to identify. The magnetic pull of a mineral may be very strong or very weak. We can also use magnets to identify iron bearing minerals.

 

Specific Gravity:

Specific gravity is a measure of the density of a mineral. We compare the density of a substance with that of water. For example, gold has the specific gravity of 19.3, and water has a specific gravity of 1. Imagine if you had two identical buckets, one with filled half-full of water and the other half-full of gold, the bucket of gold would be 19.3 times as heavy as the bucket of water.

 
Look closely at each image and the description next to it. Notice that you can describe each mineral based on observable properties.

Pyrite is a very important iron ore mineral. Many early prospectors mistook it for gold, hence the nickname Fools' Gold.

Galena is a valuable ore for lead, since lead doesn't occur naturally by itself. Because galena is made mostly of lead, it is very heavy for its size.
Magnetite is another iron ore. Iron molecules line up north and south while in the liquid state making a natural magnet.
Sulfur occurs as an element. Man uses it in a variety of ways and it has a very distinct rotten egg smell.
Calcite is found in nature in caves, seashells, eggshells and bones. Acid will make it bubble.
Quartz is found in a lot of the rocks in earth's crust. People also like it to make jewelry.

Muscovite comes in light colored paper-like sheets. Early settlers used large sheets as windows in their homes.

Biotite is a dark version of muscovite
Hematite is an iron ore mineral. It has a distinctive red streak (even though the mineral sometimes is black!) You have probably seen it as metallic black jewelry.
Talc is a familiar mineral, best know for being talcum powder (baby powder)

Hornblende is a very dark, fibrous mineral found in many rocks

Feldspar is the largest rock forming mineral. It is found in a variety of colors.
Graphite is made of the same element as diamonds but it is really soft. It is used as a dry lubricant and also as the "lead" in your pencil.
 

Now that you have learned about the different minerals, it is time to try to identify them in a lab situation. Good luck!

In this activity, you will be studying minerals and how to identify them. Remember, a mineral is a naturally formed substance. You can identify a mineral by its properties including: color, hardness, luster, streak, and even by some unique properties such as smell. You will identify the minerals using a simple dichotomous key.

 

Materials:

  • Steel Nail

  • Streak Plate
  • A variety of minerals from the following list:
    • Pyrite,
    • Galena
    • Magnetite
    • Sulfur
    • Calcite
    • Quartz
    • Biotite
    • Hematite
    • Muscovite
    • Talc
    • Hornblende
    • Graphite
    • Feldspar (Plagioclase, or Orthoclase)
 
Safety concerns: This lab is about mineral Identification not about the aerodynamics of rocks or the practice of ancient surgical procedures using only a sharp object like a nail. Please remember that minerals get very lonely without their fellow minerals due to the fact that they are gregarious in nature. So, please make sure that after the activity all minerals are placed back with their loved ones. As with all science lab activities, the most important safety rule is to follow all teacher directions.
 

Procedure.

  1. Do not break or harm the minerals in any way!
  2. Use a different number for the identification of each mineral you test .
  3. As you are given a mineral, take a few seconds to look at its properties before you start.
  4. Read the first question of the Get a Clue dichotomous key.
    • Click on yes or no as it pertains to the mineral you are looking at.
    • You will automatically be taken to the next screen.
    • Keep doing this until the screen tells you what your mineral is.
    • Write the name of the mineral next to the appropriate number and write any other information that will help you remember what the mineral is.
  5. Continue identifying each mineral (remember to start at the first question of the Get a Clue dichotomous key.)
 
You may printout a .pdf version of the "Get a Clue" dichotomous key to use if you wish.
 
Visit Pioneer Library and search e-Media for the video "Geologists Notebook: What exactly are minerals?"
 

Analysis.

  1. In what ways are minerals similar to one another?
  2. What differences did you discover as you identified the minerals?
  3. Which mineral was the easiest to identify?
  4. Which mineral was the hardest to identify?
 
Extension:

Obtain five new minerals (examples: halite, gypsum, limonite, bauxite, and fluorite.)

  • Add to the dichotomous key using these new minerals!

Review Science safetey rules here.

Get the plug-ins: Get Adobe Acrobat Reader , and Get Quicktime Player. (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

  1. The title of the activity
  2. The URL (Internet address)
  3. Your name.

Remember that no pictures can be used that show student faces or student names on it. 

Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 8th grade science core.


Updated October 24, 2008 by: Glen Westbroek

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