The Moh’s Scale

mohs hardness scale

The Moh’s Scale.  If you have been around gems and jewelry, you have probably heard reference to the Moh’s Scale. What does this mean?  Basically it indicates how hard (or soft) a stone is.  For example, the harder the stone, the better to resist scratching or wear.  All stones can be tested.  Once tested they are classified using the Moh’s scale. The man responsible for devising this scale was  Friedrich Mohs’.  According to Wikipedia, Friedrich Mohs, born German in 1773.  Mohs studied at Physics, Chemistry and Mathematics at the University of Halle/Saale.

Early Life

The area that Mohs is most known for is Mineralogy and Geology.  After the University of Halle, Mohs went on to study at a mining academy at Freiberg.  It is here Mohs took up his loves for all rocks, in part due to his mentor, Abraham Werner.    Werner, recognized in his own right, taught Mohs’ all he knew and the two would remain friends throughout their lifetime.

The first job Moh’s took after graduation was in Austria.   He became an administrator for a private mineral collection, owned by a banker, named J.F. van der Null.  Mohs was hired to organize and categorize this huge collection.  Additionally, he  wanted Mohs to identify many unknown minerals in his collection.  Thus, it is this pivotal moment that changed the direction of Moh’s life.  In addition, at this point in time there was no system for identification of minerals.

The Moh’s Scale

Moh’s started out by examining the physical properties of the different minerals.  He noted that the range of stones went from extremely soft to hard.  Also Moh’s observed how the harder stones could scratch the softer ones.  Therefore Moh’s set out to determine a way to rank hardness of minerals.  Simply put, he developed a scratch test.

Basically he began with creating a scale of increasing hardness from one to ten as follows: talc, 1; gypsum, 2; calcite, 3; fluorite, 4; apatite, 5; feldspar, 6; quartz, 7; topaz, 8; corundum, 9; and diamond, 10. Intermediate degrees of hardness were subsequently added to the Mohs scale. This scale, which has stayed with us up to present day, was not immediately embraced by miners and mineralogists of the day.  For the most part, these people were used to doing simple scratch tests in the field to determine hardness.

However it wasn’t until a paper in a noted mineralogical newspaper was published in 1820’s did the public at large take notice.  Even tho’ the paper brought notoriety to Moh’s, he continued to upgrade and improve his findings.  This included his working with crystals and determining their  external symmetry. In conclusion, Fredrich Moh’s showed the world a new way to classify both minerals and crystals.

His foresight in running extensive tests to verify theories (and as noted earlier), his work still holds up today.  Bravo Mr. Moh’s, the world owes you a debt of gratitude.