How hard is a mineral?   Geoscientists still use mineral hardness as a way to identify an unknown mineral.  This process of using mineral hardness was perfected by a German called Mohs in the early 1800’s.

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Friedrich Mohs

Friedrich Mohs was born in Gernrode, Germany in 1773. As a young man he studied chemistry, mathematics and physics at the University of Halle and also studied at the Mining Academy in Freiberg, Saxony. He then worked in a mine then moved to working for a wealthy banker who employed Mohs to identify the specimens in his collection. Later on he worked in a science museum.

Mohs followed a very old tradition of using physical properties to identify minerals rather than just trying to work out the minerals chemistry. One such method had been to look at how hardness of a mineral.

 

Mohs took this idea and created a scale of hardness of known minerals, with Diamond being the hardest at 10 and Talc being the softest at 1.  The full scale is:

10. Diamond
9. Sapphire (Corundum)
8. Topaz
7. Quartz
6. Orthoclase
5. Apatite
4. Fluorite
3. Calcite
2. Gypsum
1. Talc

And so this is the famous Mohs Scale of Hardness.

As a young geologist I learned this scale using a mnemonic :

The (talc)
girls (gypsum
can (calcite)
fight (fluorite)
and (Apatite)
order (orthoclase)
queens (quartz)
to (topaz)
sacrifice (sapphire)
diamonds. (diamond)

You can buy small hardest test kits that contain these minerals to use in the classroom.  However, I think that it is the CONCEPT that is more important for students to understand.  That concept is that all substances have a relative hardness, and they can perform a simple experiment to place those substances into a hardness order.

Here is a classroom activity that you can try with your students.

And of course, you can wear Mohs Scale with pride..

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How hard is mineral hardness?

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