Rock Cycle - Minerals (6B)
Pre Lab 

  • Determining specific gravity.
  • Distinguishing between weight, density, and specific gravity.
  • density
  • specific gravity
  • weight
  • graduated cylinders
  • mineral specimens
  • small items like nails, washers, pennies, etc.

Students determine the specific gravity of minerals.


The specific gravity, or relative density, of a mineral is a comparison of the weight of a given volume of a mineral to the weight of an equal volume of water. If a mineral has a specific gravity of 2, this means a given specimen of that mineral weighs twice as much as the same volume of water. The specific gravity of a mineral depends on the elements which compose it and how closely the atoms of those elements are packed together. For example, the specific gravity of lead is much higher than the specific gravity of silicon because lead has a higher atomic weight. Likewise although diamond and graphite are both composed of carbon, diamond has a higher specific gravity because its carbon atoms are packed very closely together.

Specific gravity is very useful in distinguishing minerals. If a mineral has a high specific gravity it will feel heavier than another mineral of the same size. Gold, for example, has a higher specific gravity than pyrite or "fools’ gold."

Density and specific gravity are sometimes used interchangeably. However, density is a measurement of the weight of a substance per some unit volume grams per cubic centimeter, whereas specific gravity is a ratio with no units. Specific gravity is a relative measurement. Weight is also different from specific gravity. Weight is the heaviness of something, measured in pounds or grams, with no relationship to a given volume.

  1. Explain the differences between specific gravity, density, and weight.
  2. Have students compare the specific gravity of mineral samples. This is accomplished by comparing two samples that are roughly the same size. Have the students hold one sample in each hand; the one that feels "heavier" has a higher specific gravity. Have the students rank the samples from highest to lowest specific gravity.
  3. You may want students to bring 10 small items that are all about the same size from home, such as like nails, screws, or buttons. Have them arrange the objects in order from highest to lowest specific gravity. It may help to have students work together. The more a student compares and contrasts the specific gravity of different objects, the easier it will be for them to determine the specific gravity of minerals. Geologist develop a "feel" for the specific gravity. Early miners knew that gold was heavier, and could easily make the comparison as they learned to distinguish gold from pyrite. Your students need to be miners, and acquire the technique.

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