Name Class Date

Identification of Minerals Activity: Hardness

Background Information: The hardness of a mineral sample is a useful characteristic to aid in identification of minerals. Moh’s Table of Mineral Hardness measures the “scratchability of a substance on a scale of 1 to 10 with 10 being the hardest (diamond) and 1 being the softest (talc). A harder mineral will scratch a softer mineral. A softer mineral will leave a mark (pulverized mineral) on a harder mineral. Certain substances have a known hardness and are used as comparisons to help identify the hardness of other minerals.

Below is Moh’s Table of Mineral Hardness.

Substance / Hardness
Talc / 1
Gypsum / 2
Fingernail / 2.5
Calcite / 3
Penny / 3.5
Fluorite / 4
Apatite / 5
Iron nail, Glass / 5.5
Feldspar / 6
Steel file / 6.5
Quartz / 7
Topaz / 8
Corundum / 9
Diamond / 10

Objectives: To test, determine,and describe the hardness of various minerals.

To use the property of hardness to classify and identify mineral samples.

Materials: mineral samples, penny, iron nail, fingernail, glass, porcelain scratch plate, steel.

Procedure:

  1. Collect mineral samples and spread them out on the lab table.
  2. Test each sample for hardness. This is done by comparison. Use the items with known hardness to compare with your samples.
  3. Test each sample against several known substances.
  4. For example: if a nail scratches the mineral then the mineral hardness must be less than the 5.5 hardness of the nail, so then test with the penny to determine if the mineral is harder or softer than the 3.5 hardness of the penny; if the sample scratches the glass then it must be harder than the glass, so then test with the scratch plate and see if the sample is harder or softer than the 7.0 hardness of the scratch plate.
  5. You may also compare one mineral sample to another mineral sample that you know the hardness of.
  6. Record your results and be sure to describe how you determined the hardness.
  7. Answer discussion questions.
  8. Use the Mineral Identification Key to try and determine the name of your sample.

Data:

Sample #, Name / Hardness / How Hardness Was Determined
1
2
3
4
5
6
7
8
9
10
11
12
13

Discussion Questions:

  1. Was it more difficult to determine the hardness of some samples than it was for others? Explain.
  2. Why would the hardness of a mineral not be considered an exact value?
  3. How do you think it would be possible for two samples of the same mineral to have different hardness values?
  4. Why would knowing the hardness of a mineral be useful information?