What is the Mohs Scale of Hardness?

The Mohs Scale of Hardness is a widely used qualitative scale for measuring the hardness of minerals. Developed by German mineralogist Friedrich Mohs in 1812, this scale ranks minerals from 1 to 10 based on their ability to scratch one another.

The Mohs Scale: From Talc to Diamond

The scale includes ten different minerals, each representing a specific level of hardness. These minerals are ranked in order, with talc being the softest and diamond being the hardest. Here’s the complete list of the minerals on the Mohs Scale, along with their corresponding hardness levels:

Talc: 1

the softest mineral on the scale. Talc can be easily scratched by a fingernail, making it the most vulnerable of all the minerals in terms of hardness.

Gypsum: 2

can be scratched by a fingernail but not by a copper coin. Gypsum is slightly harder than talc and is easily scratched by less hard substances.

Calcite: 3

can be scratched by a copper coin. Calcite is harder than both talc and gypsum and can leave a scratch on them.

Fluorite: 4

can be scratched by a knife. Fluorite is harder than calcite and can leave a scratch on minerals that are softer than it.

Apatite: 5

can be scratched by a steel file. Apatite is harder than fluorite and can leave a scratch on minerals that are softer than it.

Orthoclase Feldspar: 6

can be scratched by a glass plate. Orthoclase feldspar is harder than apatite and can leave a scratch on minerals that are softer than it.

Quartz: 7

can scratch glass and is difficult to scratch with a knife.

Topaz: 8

can scratch quartz. Topaz is harder than quartz and can leave a scratch on it.

Corundum: 9

is the mineral that includes sapphires and rubies. Corundum is harder than topaz and can scratch it.

Diamond: 10

is the hardest known natural material and can scratch all other materials. Diamond is significantly harder than corundum.

Using the Mohs Scale for Mineral Identification

The Mohs Scale is not linear, and the difference in hardness between minerals increases as you go up the scale. For example, a diamond (10) is significantly harder than corundum (9). This scale is widely used in geology and mineralogy to identify and classify minerals based on their physical properties.

How to Perform a Scratch Test

To determine the hardness of a mineral using the Mohs Scale, you can perform a scratch test. This involves scratching the mineral with another mineral that is known to be harder and observing whether it leaves a scratch. For example, if a mineral can be scratched by calcite but not by fluorite, its hardness is between 3 and 4 on the Mohs scale.

Practical Applications

Understanding the Mohs Scale and its practical applications is crucial in various fields, including geology, gemology, and materials science. It helps geologists identify and classify minerals, assists gemologists in evaluating the durability of gems, and enables materials scientists to choose appropriate materials for specific applications based on their hardness requirements.

Conclusion

The Mohs Scale of Hardness is a powerful tool in mineralogy and other scientific fields. Its simplicity and effectiveness make it an invaluable method for determining the relative hardness of minerals. Whether you are a geologist, a mineral enthusiast, or a material scientist, understanding the Mohs Scale can enhance your knowledge and facilitate your work.