Mohs Hardness testing

Mohs Hardness Test

The Mohs Hardness Test is a scratch resistance test used to determine the hardness of minerals and materials. It was developed by Friedrich Mohs in 1812 and ranks materials on a scale from 1 (softest) to 10 (hardest) based on their ability to resist scratching.

1. Principle of Mohs Hardness Test

• A material is tested by scratching it with a reference material of known hardness.

• If the reference material scratches the test material, it means the reference material is harder.

• If the test material resists scratching, it is equal or harder than the reference material.

• The hardness value is determined by the hardest material that can scratch the test surface.

2. Mohs Hardness Scale (1 to 10) 

3. How to Perform the Mohs Hardness Test

Step 1: Select Reference Materials

• Use standard Mohs hardness materials or everyday objects (e.g., a fingernail, steel knife, or glass).

Step 2: Scratch the Test Material

• Hold a reference material (e.g., quartz = 7) and try to scratch the test material.

• If a visible scratch appears, the test material has a hardness below 7.

• If there is no scratch, try with a harder material (e.g., topaz = 8).

Step 3: Determine the Hardness Range

• The highest reference material that does NOT scratch the test material gives the Mohs hardness value.

4. Example Mohs Hardness Values for Common Materials 

5. Advantages of Mohs Hardness Test

✔ Simple and easy to perform.
✔ No special equipment required.
✔ Useful for field testing of minerals.

6. Limitations of Mohs Hardness Test

❌ Not precise for industrial materials (lacks numerical accuracy).
❌ Cannot distinguish between materials with close hardness values.
❌ Not useful for metals and engineered materials (uses scratch resistance rather than indentation testing).

7. Applications of Mohs Hardness Test

• Geology & Mineralogy – Identifying minerals in the field.

• Jewelry Industry – Checking gemstone hardness.

• Glass & Ceramics – Determining scratch resistance.

• Abrasives & Cutting Tools – Selecting appropriate materials for grinding and machining.