Mohs scale of mineral hardness

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 mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. The scale ranges from 1 to 10, with 1 being the softest (talc) and 10 being the hardest (diamond). Because the Mohs scale is a relative scale, the difference between the hardness of a diamond and that of a ruby or sapphire is much greater than the difference in hardness between calcite and gypsum.

Scale of Hardness

The Mohs scale of hardness is as follows:

1. Talc (Mg3Si4O10(OH)2)
2. Gypsum (CaSO4·2H2O)
3. Calcite (CaCO3)
4. Fluorite (CaF2)
5. Apatite (Ca5(PO4)3(OH,Cl,F))
6. Orthoclase Feldspar (KAlSi3O8)
7. Quartz (SiO2)
8. Topaz (Al2SiO4(F,OH)2)
9. Corundum (Al2O3)
10. Diamond (C)

Applications

The Mohs scale is used in geology, mineralogy, and gemology for identifying mineral specimens, determining tool materials, and understanding wear resistance of materials. Despite its lack of precision, the Mohs scale is relevant for field geologists, who use portable mineral testing kits to quickly assess the hardness of minerals.

Limitations

The Mohs scale's simplicity and lack of quantitative precision make it unsuitable for engineering materials where measurements of hardness are crucial. Modern tests, such as the Vickers hardness test and the Brinell scale, offer more accurate and quantitative results.

See Also

• Mineralogy
• Geology
• Hardness
• Vickers hardness test
• Brinell scale