Mohsskála

Mohsskála, or the Mohs scale of mineral hardness, is a qualitative scale used to compare the relative hardness of minerals. Developed by Friedrich Mohs in 1812, it provides a simple framework for mineral identification in geology, fieldwork, and education. The scale orders common minerals from softest to hardest based on scratch resistance, rather than a precise numerical measurement of force.

The test works by scratch comparison: a mineral can scratch another if its Mohs value is greater than or equal to the value of the other mineral. For example, quartz (Mohs 7) can scratch fluorite (Mohs 4), while fluorite cannot scratch quartz. The standard reference minerals, listed from 1 to 10, are talc (1), gypsum (2), calcite (3), fluorite (4), apatite (5), orthoclase feldspar (6), quartz (7), topaz (8), corundum (9), and diamond (10).

Limitations of the scale include its ordinal and non-linear nature; the hardness difference between successive minerals is not uniform. Results can be influenced by impurities, grain size, surface roughness, and directional differences in some minerals (anisotropy). The Mohs scale provides a rough, qualitative indication of hardness rather than an exact measurement. For precise values, indentation hardness tests such as Vickers, Knoop, or Rockwell are used, or quantitative scratch tests with controlled forces.

Despite its limitations, the Mohs scale remains a foundational tool in mineralogy, widely used for quick identification, educational purposes, and in gemology to gauge durability and care requirements.