1. The Scale: The Mohs Hardness Scale is a relative scale that compares the resistance of a mineral to scratching. It consists of 10 minerals, ranked from softest (1) to hardest (10).
* 1: Talc (easily scratched by your fingernail)
* 2: Gypsum (scratched by a fingernail)
* 3: Calcite (scratched by a copper coin)
* 4: Fluorite (scratched by a steel knife)
* 5: Apatite (scratched by a steel knife, but less easily)
* 6: Orthoclase (scratches glass)
* 7: Quartz (scratches steel)
* 8: Topaz
* 9: Corundum
* 10: Diamond (the hardest known natural mineral)
2. The Test: To determine the hardness of an unknown mineral, a scientist uses a set of known minerals from the Mohs scale. They try to scratch the unknown mineral with each known mineral, starting with the softest.
* If the unknown mineral is scratched by a known mineral, it is softer.
* If the unknown mineral scratches a known mineral, it is harder.
3. Finding the Hardness: The scientist continues this process until they find two known minerals: one that scratches the unknown mineral, and one that doesn't. The unknown mineral's hardness is then assigned a number between the two known minerals.
For example:
* If an unknown mineral can be scratched by a steel knife but not by a copper coin, its hardness is between 3 and 5.
* If the unknown mineral can scratch glass but not quartz, its hardness is between 6 and 7.
Important Notes:
* The Mohs Hardness Scale is a relative scale, not an absolute one. This means the difference in hardness between two minerals is not always proportional to the difference in their scale numbers. For example, diamond (10) is much harder than corundum (9), while the difference in hardness between talc (1) and gypsum (2) is much smaller.
* The test relies on the ability of the mineral to leave a scratch. Some minerals may be brittle and break instead of scratching, making this test inaccurate.
* This test is useful for field identification of minerals, but more precise methods are used in laboratory settings.
By using the Mohs Hardness Scale, scientists can easily identify the hardness of a mineral, which is a crucial characteristic for understanding its properties and uses.
