Friedrich Mohs & The Mohs Scale of Gemstone Hardness

Friedrich Mohs

Friedrich Mohs is famous in the gem world as the creator of the Mohs scale of mineral hardness. His scale is still widely used today. But who was Friedrich Mohs and how did he come to create his scale?

Mohs was born to a merchant's family in the town of Gernrode, Germany in 1773. After attending school at Halle, he went on to study at the mining academy at Freiberg, where he was greatly influenced by his teacher, Abraham Werner. Werner inspired the young Mohs with a lifelong interest in mineralogy and geognosy; the geological study of materials forming the earth.

In 1801, Friedrich Mohs relocated to Austria and took on two distinct roles. Firstly, he served as a foreman at the Neudorf Mine in the eastern Harz Mountain area. However, it was his second position that truly captivated Mohs due to his deep interest in rocks. He was engaged by a wealthy Austrian banker named J.F. van der Null, who possessed an extensive mineral collection requiring curation. Mohs' responsibility involved organizing the collection into distinct categories and identifying any materials that remained unidentified.

This was a great challenge for Mohs because at that time, there was no accepted method for categorizing minerals. Therefore, by using the same reasoning as botanists, who sort plants with similar physical characteristics into genus groups, Mohs began examining the minerals for common properties that would allow him to classify them.

Although this approach was widely criticized by the mineralogical establishment at the time, it would ultimately bring him fame, since one of the main physical properties Mohs concentrated on was the hardness of the material in question.

Mohs noted that certain minerals could be used to scratch the surface of other minerals, so he reasoned that this scratch test could be used to rank minerals by their hardness. In this way he eventually ranked all the minerals according to their hardness. The scale ranged from the softest mineral; talc, to the hardest; diamond.

Around 1810 Mohs gave up his job as mine foreman and in 1812 he became professor of mineralogy in Gratz, where he finalized his work on hardness. Creating a scale of one to ten, he assigned a value to each mineral. This was to become the Mohs Scale of Hardness.

In 1817, after the death of Werner, Mohs replaced his mentor and became a tutor at the mining academy in Freiberg, where he worked for nine more years until he was appointed professor of Mineralogy at the University of Vienna. Mohs ended his remarkable career as a mining advisor at the Mining University in Leoban and died aged 66, whilst holidaying in Italy.