Glossary

The Mohs Hardness Scale is a comparative scale that measures the relative hardness of minerals and other materials based on their ability to resist scratching. It was developed in 1812 by German mineralogist Friedrich Mohs and is still widely used today as a quick, practical way to rank material hardness. The scale ranges from 1 to 10, with 1 being the softest and 10 the hardest. Each mineral on the scale can scratch any material ranked lower than itself, but not those higher.

At the soft end, talc is ranked at 1, meaning it can be easily scratched by any other mineral. At the hardest end, diamond is ranked at 10, representing the maximum hardness in natural materials. Other familiar examples include gypsum (2), calcite (3), fluorite (4), apatite (5), feldspar (6), quartz (7), topaz (8), and corundum (9, which includes sapphires and rubies).

The Mohs Scale is not linear but ordinal, meaning the difference in hardness between successive numbers is not equal. For example, diamond (10) is much harder compared to corundum (9) than corundum is compared to topaz (8). Despite this, the scale is practical for fieldwork and industry because it gives a fast and simple way to test hardness using scratch comparisons.

In the context of fasteners and industrial applications, the Mohs Hardness Scale is relevant for understanding wear resistance, abrasion resistance, and material compatibility. For example, coatings, cutting tools, and surface treatments are often selected based on hardness relative to the materials they will interact with. While engineers often use more precise hardness measures such as Rockwell, Vickers, or Brinell hardness tests, the Mohs scale remains a useful reference for comparing material durability in general terms.