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Mineral Specific Gravity

Specific Gravity is a measure of the density of a mineral compared to the density of an equal volume of water. To determine specific gravity, you will use the following formula:

 

____________Weight of Mineral in Air___________
(Weight of Mineral in Air) - (Weight of Mineral in Water)

 

Mineralogists use a simple scale called a Jolly Balance. You can create your own Jolly Balance by using some basic materials you have at home or in your laboratory: ruler, spring, string, pencil or stick, two wooden blocks or stacks of books, and a jar filled with water.

Tie a mineral specimen to a string and tie the other end of the string to the spring on your Jolly Balance. Let the mineral hang down and record the reading indicated by the paper clip pointer on your ruler. Be as accurate and precise as possible (for instance, measure to the nearest 1/16th of an inch rather than the nearest 1/8th of an inch). Raise the mineral and place the beaker of water under the mineral. Let the mineral hang down into the beaker of water. Record the reading indicated by the paper clip pointer, again to the nearest 1/16th of an inch. These are the two numbers you need to calculate the Specific Gravity. Use the formula above.

Below: A Jolly Balance you can make from common items in your home or lab. (Stick, books or blocks, string, spring, paper clip, ruler)

Jolly Balance

 

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