Mohs scale

Mohssche-haerteskala hg

Mohs-Hardness-Graph

Talc block

Gypse Arignac

Calcite-sample2

Mohs scale of mineral hardness is a qualitative ordinal scale that characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of the several definitions of hardness in materials science.

Overview

The Mohs scale of hardness is based on the ability of one natural sample of mineral matter to scratch another. The scale ranges from 1 to 10, with 1 being the softest (talc) and 10 being the hardest (diamond). This scale is a purely ordinal scale, meaning that it only sequences the hardness of minerals; it does not quantify the difference in hardness between them. For example, diamond (10) is four times as hard as corundum (9), which is twice as hard as topaz (8).

Scale of Hardness

The standard scale assigns a hardness score to 10 minerals, with many other minerals being compared to these standards. Here is a simplified list of the Mohs scale:

1. Talc (1)
2. Gypsum (2)
3. Calcite (3)
4. Fluorite (4)
5. Apatite (5)
6. Orthoclase Feldspar (6)
7. Quartz (7)
8. Topaz (8)
9. Corundum (9)
10. Diamond (10)

Each mineral can scratch the ones below it on the scale. For instance, apatite can scratch fluorite but not quartz.

Applications

The Mohs scale is used in geology, mineralogy, and gemology for identifying mineral specimens, testing gemstone durability, and understanding the wearability of materials. It helps in determining the suitability of minerals for various industrial and jewelry purposes.

Limitations

While the Mohs scale is widely used for its simplicity and ease of use, it has several limitations. The scale is not linear, and the steps between each mineral are not equal. Additionally, the scale is less relevant for materials engineering, where more quantitative measures of hardness such as the Vickers, Brinell, and Rockwell scales are used.

See Also

• Mineral
• Hardness
• Friedrich Mohs
• Materials science
• Gemology

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