The Density of Minerals

By Stu Grove on May 26, 2015

For this year’s Science Fair, Introductory Physics student Shae K. began by pondering whether it would be possible to identify a mystery sample of different minerals by formulating their density, given the knowledge that a specific substance’s density will remain unchanged regardless of a change in its mass. Due to the fact that minerals do not often come in perfect cubic form, Shae realized that in order to take a precise measurement of each minerals volume (needed to calculate density) he would have to utilize the water displacement method. Fascinated by this rather unique (and very fun!) form of quantification, Shae traced the origins of this method to Archimedes and his famous bathtub story. During the fair Shae enthusiastically discussed the necessary tools needed to perform the method and the procedure involved. Additionally, he presented his visitors with information about minerals, and discussed the value of knowing the density of a substance.
displaying a mineral used in the experiment
 
 

Scientific Question 

Can a sample of different minerals be identified by finding their density?
 

Hypothesis

I think that minerals can be identified by their density.
 
 
 

Background Information

  1. What is Density?
    • Density is how much stuff an object has in its volume. The object's density will never change. If you have a whole chocolate cake and cut it in to pieces no matter how many times you cut the cake its density will never change.   

  2. What is the Water Displacement Method?
    • The Water displacement method was discovered by a man named Archimedes. Archimedes was given the task to find out if the gold grown wreath that was given to the king was made of 100% gold. When Archimedes was taking his daily bath, he stepped into a cold tub of water to which the water began to spill out over the sides. Noticing this Archimedes began to watch the water level rise and over flow, as he submerged into the water.  He found the solution to the king’s problem. He ran out of the public baths, shouting all the way home, “Eureka!”

    • He was so excited he forgot that he had no clothes on. “Eureka” in Greek translates into, “I have found it.” He discovered how to find the volume of an irregular shaped object.       

  3. What is a Mineral? 
    • A mineral is something that is produced by the earth and not by plants, animals, or people.  Coal is not a mineral; it is made from decomposed plants that have been fossilized.

  4. How Do you Find an Object’s Density?
    • You can find the density of an object by taking its mass, which is how heavy it is, and dividing it by the volume, its size.

  5. What is Water Displacement?
    • Let's say you have a cup of water that is filled half way. Then you drop some ice cubes in the cup. Then the water rises up because the ice cubes displaced water. The amount of water that is displaced is equal to the volume of the object. By capturing this water and measuring it, using a graduated cylinder, you can find an exact measurement. You can use this number in the density formula, which is mass divided by volume.

  6. Conclusion
    • My hypothesis was that minerals can be identified by their density’s using the water displacement method and it is true. If you look at a mineral chart you will see the names of minerals, and their densities.  When you put an object in water the water will rise. The reason for this is because the of the objects volume. If you take something that has volume of 10 cubic cm the water level will increase by 10 ml.  Dropping minerals in an overflow tank fill beneath the spout will make the water rise causing it to go out the hole.  In conclusion the identity of a mineral and its density can be found using the water displacement method.

 
adapted graduated cylinder and beakershaw holding a scaleShae holding a stone
 
tray holding all of his lab supplies

Materials

  • an apron
  • eye protection
  • overflow tank
  • capture bucket
  • paper towels
  • minerals
  • funnel
  • minerals chart
  • graduated cylinder
  • talking scale.
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