Hardness Scale

Posted by in Best Of, Musings




Pretty typical of how most of my musings begin, I was wandering through the corridors of my labs, thinking about random things.  As I turned the corner, I grazed my hand along the edge of the concrete wall, and piece of concrete crumbled off effortlessly.  Once I was passed the initial feelings of guilt, surveying the halls to see if anyone else noticed, I became transfixed by the texture of the concrete, and how easy it was to crush between my finger tips.

I began to recall the Hardness Scale, which I later relearned is called the Mohs Scale of Mineral Hardness, that talked about how “hard” a mineral substance is compared to others.  From what I remembered, I knew Diamond was the hardest substance, and that the scale was on a 1-10 scale.  The scale is pretty arbitrary since it only compares the hardness between the minerals Mohs initially used, and doesn’t reflect the absolute hardness in definable units.  Yet with the development of precision scientific instruments, the “hardness” of a substance is now more accurate and comparatively scalable.

After doing some online research (if you wanna call it that), I have find quite a lot of literature about the hardness of materials.  The Standard International (SI) units of hardness are in pascals (Pa = kg/m s2), which happen to be the same units as pressure.  There also appears to be multiple types of hardness, the three main definitions are scratch hardness (the method used by Mohs in his experiment), indentation hardness and elasticity hardness.  There are multiple scales to measure hardness, which include using a sclerometer scratch scale, Rockwell indentation scale, and Bennett rebound hardness scale, just to name a few.  There are five general techniques to make materials harder: Hall-Petch strengtheningwork hardeningsolid solution strengtheningprecipitation hardening, and martensitic transformation.  Also, other important words are used to further define a materials hardness; these words include strength, ductility, brittleness and toughness.  (If you are interested in material science, I highly recommend pursuing through the above links.  However for the sake of brevity, I chose to gloss over the details).

I also came across another shocking bit of information–diamonds are no longer the hardness substance on earth!  According to this articlewurtzite boron nitride and lonsdaleite (hexgonal diamond) are even harder than naturally occurring tetrahedral diamonds.  I feel betrayed, just like the day Pluto was reclassified as an asteroid, and no longer considered a planet!

So there you have it.  Everything you’d ever need, or want, to know about hardness.  And thanks to the internet, it was even that HARD to find everything I needed. 😉