- HARDNESS EXERCISE C -
USING THE MOHS SCALE TO DETERMINE THE HARDNESS OF NON-MOHS MINERALS
INTRODUCTION: In Exercise B, you determined the relative hardnesses of the minerals that define the points on the Mohs Scale. The Mohs hardness of any other mineral may be established by determining between which two Mohs minerals the hardness of the mineral lies. In the example shown on the right, mineral 'X' is harder than Mohs Scale mineral 7 and softer than Mohs Scale mineral 8. It may have a value such as H = 7.5.

It is also possible for a non-Mohs mineral to have a hardness exactly equal to the hardness of one of the Mohs Minerals. In that case, its hardness will be a whole number.

Determining the Mohs hardness of an unknown may be an important aid to identifying it. For example, the minerals apatite and beryl may be very similar in appearance, but apatite has a hardness of H = 5, while the hardness of beryl is 7.5 to 8. Thus, a simple hardness test may serve to distinguish them.


What you have to do is this:

  1. After you have read these instructions (1 through 4), you will go to the Virtual Hardness Testing Lab. There you will see the Hardness Evaluation Table.

    • HOW THE TABLE WORKS: A sketch (not the real thing) of the Table is shown on the right. The Table has two identical lists of mineral specimens and testing tools: one on the left (List 1) and one on the right (List 2). The Mohs mineral specimens are marked with asterisks *.

    • On the real Table, you will click on the buttons to choose a different mineral from each list. Pictures of the two minerals will appear in the top two boxes.

    • Then you will press the "SCRATCH" button. Pictures of the same two mineral specimens will appear in the lower two boxes. The softer of the two minerals will have a scratch on it. A message will appear in the message box.

  2. WHAT TO DO: For all of the minerals that you have been assigned that appear on the Hardness Evaluation Table, follow steps (a) through (d). Keep a record of your results (the numbers of the specimens tested and their hardnesses) on a piece of paper.
    1. Test the specimen against each of the Mohs minerals. The Mohs minerals are marked with asterisks *.

    2. If there is a Mohs mineral which it doesn't scratch and which doesn't scratch it, then they have the same hardness.

    3. Otherwise, determine between which two Mohs minerals the hardness of the specimen falls. (For example: Specimen # 16 is scratched by # 6* (H = 3) and all harder Mohs minerals; but it scratches # 12* (H = 2) and all softer Mohs minerals. Thus, the hardness of Specimen # 16 falls between H = 2 and H = 3.

    4. Assign a hardness number to your choice. (For example: Specimen # 16 can be assigned a hardness greater than 2 but less than 3, such as H = 2.5.)

  3. After you have finished testing, return to this page. Enter your results in the 'interactive' Answer Checking Table (see the purple button below) to see if they are correct

  4. If they are correct, record the mineral specimen numbers and their Mohs hardnesses in Part C of the HARDNESS EXERCISES WORK SHEET (MN-3).

NOW THAT YOU'VE READ THE INSTRUCTIONS, CLICK ON THE GREY BAR BELOW AND....
Go to the Answer Checking Table

© 2001, David J. Leveson